STOICHIOMETRY

STOICHIOMETRY

PHYSICAL CHEMISTRY

Digital Chemistry labs Pvt Ltd403 Maha Laxmi Plaza Jawahar Nagar

Kota (Raj.) Pin :- 324005Phone :- 9929617387Fax :- 0744 - 2405300

www.digitalchemistrylabs.comemail:[email protected]

www.digitalchemistrylabs.com

Digital Chemistry labs Pvt Ltd403 Maha Laxmi Plaza Jawahar Nagar Kota (Raj.) Pin :- 324005

Phone :- 9929617387 Fax :- 0744 - 2405300

THE KEYThe mole :

The mole is the unit invented to provide a simple way of reporting the huge numbers the “massive heaps”of atoms and molecules in visible samples. It would be inconvenient to refer to large numbers like2 ×1025 atoms, just as wholesalers would find it inconvenient to count individual items instead of dozens(12) or gross (144).

1 mole is number of atoms in exactly 12 gm of carbon – 12. One mole in broader terms applied to ions,molecules, electrons refer to 6.023 × 1023 of any objects also called as Avogadro number.

so mole = 2310023.6

objectsorentitiesof.no

It is very big unit. For instance, 1mole of chemistry textbooks would cover the surface of the earth to aheight of about 300 Km. While defining mole always state explicitly the identity of the particles to whichthe term moles refers.

Mole-mass relation:

1 mole or gm object is molar mass of substance. For example 1 mole sodium refers to its molar mass23 gm or 1 mol H2 refers to its molar mass 2 or 1 mole CO2 refers to its molar mass 44.

mole = substanceofmassmolar

substanceanyofmass

Average molar mass:

Every element in nature exist along with its isotopes. So when we refers to molar mass, it means averagemolar mass i.e.

Average molar mass = % of isotope × molar mass of isotope.

Mole volume relation:

1 mole means 22.4 litre of volume occupied by that entity at S.T.P. (0°C, 1 atm pressure)

mole = litre4.22

STPatsubstanceanyof.vol

Sometimes data is not given at STP, so we calculate no. of moles with the help of ideal gas equation

PV=nRT or calculate the volume under that condition with the help of relationP VT

P VT

1 1

1

2 2

2

* We can convert any volume into mole by dividing it with 22.4 litre only when it is specified in thenumerical at STP otherwise we can not.

* Mole of any substance calculated are independent of temperature, pressure etc. because it representamount of substance which is not going to change.

Mole - mass – volume relations:

We can find the no. of atoms in 1 litre of any gas at STP by converting it through mol. So mole is standardunit through which you can find mass of any volume or volume for any mass at STP.

Mole in compounds:1 mole compound AxByCz refers to X mole of A, Y mole of B and Z mole of C entities. It can be ions forionic compound or it can be atom in covalent compound .

mailto:email:[email protected]


Phone :- 9929617387 Fax :- 0744 - 2405300

Stoichiometry

Stoichiometry pronounced (“stoy – key – om – e – tree”) is the calculations of the quantities of reactantsand products involved in a chemical reaction.

This can be divided into two category.(A) Gravimetric analysis(B) Volumetric analysis

(A) Gravimetric Analysis :

In this we are concerned with calculations involving either(a) mass - mass relationship(b) mass-volume relationship(c) volume - volume relationship

Method :

If we know the balance chemical equations then we can adopt the simple mole method in which werelate reactants and products in their stoichiometric mol ratio. If we do not know balanced reactions wecan adopt POAC (principle of atomic conversion) provided whole reactant is giving into product forwhich calculation is to be made.

Limiting Reagent:

It is very important concept in chemical calculation. It refers to reactant which is present in minimumstoichiometry quantity for a chemical reaction. It is reactant consumed fully in a chemical reaction. So allcalculations related to various products or in sequence of reactions are made on the basis of limiting reagent.

Percentage yield:

Normally a reagent is associated with some impurity due to which actual yield of product is less than thetheoretical maximum yield.

The percentage yield of product = 100yieldmaximumltheoreticathe

yieldactual

(B) Volumetric analysis :

This mainly involve titrations based chemistry. It can be divided into two major category.

(I) Non-redox system (II) Redox system

(I) Non – redox systemThis involve following kind of titrations:

1. Acid-Base titrations2. Back titration3. Precipitation titration4. Double indicator acid base titration

Concentration terms :

Volumetric calculations involves many concentration terms such as

* Density =olumeV

Mass

* Relative density = substancerefrenceofDensity

substanceanyofDensity


Phone :- 9929617387 Fax :- 0744 - 2405300

* Specific gravity = C4 water atDensity of

substanceanyofDensity

* Vapour density = pressureandre temperatusameatgasHofDensity

pressureandure temperatsomeat vapourofDensity

2

* %

W

w =

wt of solutewt of solution.. × 100

* %

V

v = 100

solutionofvolume

soluteofvolume

* %

V

w = 100

solutionofvolume

soluteof.wt

* Molarity(M) =Mole of solute

volume of solution in litre

* Molality(m) = kg)(insolventof.wt

soluteofMole

* Let 1 mole solution contain x1 mole of solute & x

2 mole of solvent.

Molarity of solution (M) =2211

1

MxMx

.x

where = density of solution (g / L)M

1 & M

2 = Molar masses (g/mole) of solute & solvent respectively.

molality (m) =22

1

M.x

x× 1000

Relation between molarity (M) & Molality (m) :

m =1M.M

M

× 1000

* Normality =gm equivalent of solutevolume of solution in litre

Where gm equivalent = factorn

mole

n factor is a conversion factor by which we can convert equivalents into mole or equivalent weight intomolar mass or vice versa.

Titrimetric Method of Analysis :

A titrimetric method of analysis is based on chemical reaction such as. aA + tT Product

Where ‘a’ molecules of “analysis”, A, reacts with t molecules of reagent T.T is called Titrant normally taken in buret in form of solution of known concentration. The solution of


Phone :- 9929617387 Fax :- 0744 - 2405300

titrant is called “standard solution”.The addition of titrant is added till the amount of T, chemically equivalent to that of ‘A’ has been added.It is said equivalent point of titration has been reached. In order to know when to stop addition of titrant,a chemical substance is used called indicator, which respond to appearance of excess of titrant bychanging colour precisely at the equivalence point. The point in the titration where the indicator changescolour is termed the ‘end point’. It is possible that end point be as close as possible to the equivalencepoint.

The term titration refer’s to process of measuring the volume of titrant required to reach the end point.For many years the term volumetric analysis was used rather than titrimetric analysis. However from arigorons stand point the term titrimetric is preferable because volume measurement may not beconfirmed to titration. In certain analysis, for example one might measure the volume of a gas.We can adopt mole method in balanced chemical reactions to relate reactant and products but it is moreeasier to apply law of equivalents in volumetric calculations because it does not require knowledge ofbalanced chemical reactions involved in sequence. Law of equivalents refers to that, equivalents of alimiting reactant is equal to equivalent of other reactant reacting in a chemical reaction or equal to equivalentsof products formed in reaction.

Balancing of chemical equation on the basis of n factor

Whenever two substances react in such a way that their n factors are in the ratio of x : y, they wouldalways react with each other in the molar ratio of y : x in a balanced chemical reaction.

Acid-Base titration

To find out strength or concentration of unknown acid or base it is titrated against base or acid of knownstrength. At the equivalence point we can know amount of acid or base used and then with the help oflaw of equivalents we can find strength of unknown.

Meq of acid at equivalence point = Meq of base at equivalence point

Back titration

Back titration is used in volumetric analysis to find out excess of reagent added by titrating it with suitablereagent. It is also used to find out percentage purity of sample. For example in acid-base titrationsuppose we have added excess base in acid mixture. To find excess base we can titrate the solution withanother acid of known strength.

Precipitation titration :

In ionic reaction we can know strength of unknown solution of salt by titrating it against a reagent withwhich it can form precipitate. For example NaCl strength can be known by titrating it against AgNO3solution with which it form white ppt. of AgCl.

So meq. of NaCl at equivalence point = meq of AgNO3 used = meq of AgCl formed

Double indicator acid-base titration:

In the acid-base titration the equivalence point is known with the help of indicator which changes itscolour at the end point. In the titration of polyacidic base or polybasic acid there are more than one endpoint for each step neutralization. Sometimes one indicator is not able to give colour change at every endpoint. So to find out end point we have to use more than one indicator. For example in the titration ofNa2CO3 against HCl there are two end points.


Phone :- 9929617387 Fax :- 0744 - 2405300

Na2CO3 + HCl NaHCO3 + NaCl

NaHCO3 + HCl H2CO3 + NaCl

When we use phenophthalein in the above titration it changes its colour at first end point when NaHCO3is formed and with it we can not know second end point. Similarly with methyl orange it changes itscolour at second end point only and we can not know first end point. It is because all indicator changescolour on the basis of pH of medium. So in titration of NaHCO3, KHCO3 against acid phenolphthaleincan not be used.

So we can write with phenolpthalein, if total meq of Na2CO3 = 1 then½ meq of Na2CO3 = meq of HCl

with methyl orange,meq of Na2CO3 = meq of HCl

Titration Indicator pH Range n factor

Na2CO3 Phenolphthalein 8.3 – 10 1 against acid

K2CO3 Methyl orange 3.1 – 4.4 2

* When we carry out dilution of solution, meq, milli mole or mole of substance does not change becausethey represent amount of substance.

Eudiometry : [For reactions involving gaseous reactants and products]

* The stoichiometric coefficient of a balanced chemical reactions also gives the ratio of volumes inwhich gasesous reactants are reacting and products are formed at same temperature and pressure.The volume of gases produced is often given by mentioning certain solvent which absorb containgases.Solvent gas (es) absorbKOH CO2, SO2, Cl2Ammonical Cu2Cl2 COTurpentine oil O3Alkaline pyrogallol O2water NH3, HClCuSO4 /CaCl2 H2O

* Check out for certain assumption which are to be used for solving problem related to this.


Phone :- 9929617387 Fax :- 0744 - 2405300

THE ATLAS


Phone :- 9929617387 Fax :- 0744 - 2405300

EXERCISE-I

Simple Application of Mole Concept

Q.1 Chlorophyll, the green colouring matter of plants responsible for photosynthesis, contains 2.68% ofmagnesium by mass. Calculate the number of magnesium atoms in 2.00 g of chlorophyll.

Q.2 When 10.0g of marble chips (CaCO3) are treated with 50 mL of HCl (d = 1.096 g/mL, the marbledissolves, giving a solution and releasing CO2 gas. The solution weights 60.4 g. How many liters of CO2gas are released ? The density of the gas is 1.798 g/L.

Q.3 105 mL water at 4°C is saturated with NH3 gas, producing a solution of d = 0.9 g/ml. If the solutioncontains 30% NH3 by wt. Calculate its volume.

Q.4 The atomic wt. of A and B are 20 and 40. If x gm of A contains Y atoms, how many atoms are presentin 2 x g of B.

Q.5 Density of a gas relative to air is 1.17. Find the mol. mass of the gas. [Mair = 29g/mol]

Q.6 Sodium chloride has a density of 2.165 g cm3 at 25°C. Calculate the no. of atoms in 1.000 cm3 ofsodium chloride at 25°C.

Q.7 A chemist puts 5 gm of a mixture of NO2 & N2O4 into a large bulb. If the sample was 50% of each bywt., how many moles of each gas are in the bulbs.

Q.8 Caffeine burns in O2 to give CO2, H2O & NO2. How many gms of O2 are required and how many gmsof NO2 would be produced from burning 1.0g Caffeine. The reaction of caffeine with oxygen is writtenas follows:2C8H10N4O2 + 27O2 16CO2 + 10H2O + 8NO2

Q.9 Equal weights of mercury and I2 are allowed to react completely to form a mixture of mercurous andmercuric iodide leaving none of the reactants. Calculate the ratio of the wts of Hg2I2 and HgI2 formed.

Concept of limiting reagents

Q.10 Titanium, which is used to make air plane engines and frames, can be obtained from titanium tetrachloride,which in turn is obtained from titanium oxide by the following process :

3 TiO2(s) + 4C (s) + 6Cl2 (g) 3TiCl4(g) + 2CO2(g) + 2CO (g)A vessel contains 4.15 g TiO2, 5.67 g C and; 6.78 g Cl2, suppose the reaction goes to completion aswritten, how many gram of TiCl4 can be produced ? (Ti = 48)

Q.11 A chemist wants to prepare diborane by the reaction 6 LiH + 8BF3 6Li BF4 + B2H6If he starts with 2.0 moles each of LiH & BF3. How many moles of B2H6 can be prepared.

Q.12 When you see the tip of a match fire , the chemical reaction is likely to beP4S3 + 8O2 P4O10 + 3SO2What is the minimum amount of P4S3 that would have to be burned to produce at least 1.0 g of P4O10and at least 1.0 g of SO2


Phone :- 9929617387 Fax :- 0744 - 2405300

Empirical and Molecular Formulae

Q.13 B105 and B11

5 are two isotopes of boron. If average mass number is 10.2. What is the % of each.

Q.14 Tha action of bacteria on meat and fish produces a poisonus compound called cadaverine. It is 58.77%C, 13.81% H, and 27.42% N. Its molar mass is 102 g/mol. Determine the molecular formula ofcadaverine.

Q.15 On combustion analysis, a 0.450 g sample of Caproic acid (contained only C,H & O) gives0.418 g of H2O and 1.023 g of CO2. What is the empirical formula of Caproic acid? If the molecularmass of Caproic acid is 116 amu, what is the molecular formula?

Atomic Weight

Q.16 A sample of metallic element X, weighs 4.315g combines with 0.4810L of Cl2 gas (at normal pressure and20°C) to form the metal chloride XCl. If the density of Cl2 gas under these conditions is 2.948 g/L. Whatis the mass of the chlorine? The at. wt. of chlorine is 35.45 amu. What is at wt of X, what is identifyof X.

Q.17 A sample of pure metal M weighing 1.35g was quantitatively converted into 1.88g of pure MO. Calculateat wt. of metal M

Q.18 Cu2S and M2S are isomorphous. The % of S in former is 20.14 and in the later 12.94. At wt ofCu = 63.57. Calculate at wt of M.

Q.19 A compound which contains one atom of X and two atoms of Y for each three atoms of Z is made bymixing 5.00 g of X, 1.15 × 1023 atoms of Y and 0.03 mole of Z atoms. Given that only 4.40 g of compoundresults. Calculate the atomic weight of Y if the atomic weights of X and Z are 60 and 80 amu respectively.

Gravimetric Method of Analysis

Q.20 A 0.6025 gm sample of a chloride salt was dissolved in water and the chloride precipitated by addingexcess silver nitrate. The precipitate of silver chloride was filtered, washed, dried, and found to weigh0.7134 gm. Calculate the percentage of chloride (Cl) in the sample.

Q.21 A 0.4852 gm sample of iron ore is dissolved in acid, the iron oxidized to the +3 state, and then precipitatedas the hydrous oxide, Fe2O3 · xH2O. The precipitate is filtered, washed, and ignited to Fe2O3, which isfound to weigh 0.2481 gm. Calculate the percentage of iron (Fe) in the sample.

Q.22 The phosphorous in a sample of phosphate rock weighing 0.5428 gm is precipitated asMgNH4PO4 · 6H2O and ignited to Mg2P2O7. If the ignited precipitate weighs 0.2234 gm, calculate

(a) the percentage of P2O5 in the sample and(b) the percent purity expressed as P rather than P2O5.

Q.23 Calculate the number of milliliters of ammonia, density 0.99 g/ml, 2.3% by weigh NH3, which will berequired to precipitate as Fe(OH)3 the iron in a 0.70 gm sample that contain 25% Fe2O3.

Q.24 What size sample which contains 12.0% chlorine (Cl) should be taken for analysis if the chemist wishesto obtain a precipitate of AgCl which weighs 0.50 gm?


Phone :- 9929617387 Fax :- 0744 - 2405300

Q.25 A 0.75 gm sample containing both NaCl and NaBr is titrated with 0.1043 M AgNO3, using 42.23ml. Asecond sample of the same weight is treated with excess silver nitrate, and the mixture of AgCl and AgBr isfiltered, dried and found to weigh 0.8042 gm. Calculate the percentages of NaCl and NaBr in the sample.

Q.26 A mineral consists of an equimolar mixture of the carbonates of two bivalent metals. One metal is presentto the extent of 13.2% by weight. 2.58 g of the mineral on heating lost 1.233 g of CO2. Calculate the %by weight of the other metal.

Q.27 Determine the percentage composition of a mixture of anhydrous sodium carbonate and sodiumbicarbonate from the following data:wt. of the mixture taken = 2gLoss in weight on heating = 0.124 g.

Q.28 A 10 g sample of a mixture of calcium chloride and sodium chloride is treated with Na2CO3 to precipitatecalcium as calcium carbonate. This CaCO3 is heated to convert all the calcium to CaO and the final massof CaO is 1.62g. Calculate % by mass of NaCl in the original mixture.

Concentration terms

Q.29 The density of a solution containing 13% by mass of sulphuric acid is 1.09 g/mL. Calculate the molarityof the solution.

Q.30 The mole fraction of CH3OH in an aqueous solution is 0.02 and its density is 0.994 g cm–3. Determineits molarity and molality.

Q.31 The density of a solution containing 40% by mass of HCl is 1.2 g/mL. Calculate the molarity of the solution.

Q.32 15 g of methyl alcohol is present in 100 mL of solution. If density of solution is 0.90 g mL–1. Calculate themass percentage of methyl alcohol in solution.

Q.33 Units of parts per million (ppm) or per billion (ppb) are often used to describe the concentrations of solutesin very dilute solutions. The units are defined as the number of grams of solute per million or per billiongrams of solvent. Bay of Bengal has 1.9 ppm of lithium ions. What is the molality of Li+ in this water ?

Q.34 Find out the volume of 98% w/w H2SO4 (density = 1.8 gm/ ml) must be diluted to prepare12.5 litres of 2.5 M sulphuric acid solution.

Q.35 10 ml of pure ethanol (d = 0.785g/ml) is diluted with water to a volume of 100ml. Find molarity.

Q.36 Calculate molality of aq. H2SO4 containing 61% by wt. of H2SO4. The density of solution is1.5091 g/cc.

Q.37 3.2665 gm of H3PO4 are present in one litre of a solution. Find normality.

Q.38 In what ratio should you mix 0.2M NaNO3 and 0.1M Ca(NO3)2 solution so that in resulting solution,the concentration of negative ion is 50% greater than conc. of positive ion.

Q.39 A 500 ml solution was prepared by dissolving 28.5 gm of MgCl2 in water. If the density of MgCl2solution is 1.2 gm/ml, calculate

(a) Molarity of Cl– ion(b) Mole fraction of Mg2+ ion(c) Concentration in ppm of Mg2+ ion


Phone :- 9929617387 Fax :- 0744 - 2405300

Acid Base Titration

Q.40 How many ml of 0.1 N HCl are required to react completely with 1 g mixture of Na2CO3 and NaHCO3containing equimolar amounts of two?

Q.41 0.5 g of fuming H2SO4 (oleum) is diluted with water. The solution requires 26.7 ml of 0.4 N NaOH forcomplete neutralization. Find the % of free SO3 in the sample of oleum.

Q.42 H3PO4 is a tri basic acid and one of its salt is NaH2PO4. What volume of 1 M NaOH solution should beadded to 12 g of NaH2PO4 to convert it into Na3PO4?

Q.43 1.64 g of a mixture of CaCO3 and MgCO3 was dissolved in 50 mL of 0.8 M HCl. The excess of acidrequired 16 mL of 0.25 M NaOH for neutralization. Calculate the percentage of CaCO3 and MgCO3 inthe sample.

Q.44 1.5 g of chalk were treated with 10 ml of 4N – HCl. The chalk was dissolved and the solution made to100 ml 25 ml of this solution required 18.75 ml of 0.2 N – NaOH solution for complete neutralisation.Calculate the percentage of pure CaCO3 in the sample of chalk?

Double titration

Q.45 A solution contains Na2CO3 and NaHCO3. 20ml of this solution required 4ml of 1N – HCl for titrationwith Ph indicator. The titration was repeated with the same volume of the solution but with MeOH.10.5 ml of 1 – N HCl was required this time. Calculate the amount of Na2CO3 & NaHCO3.

Q.46 A solution contains a mix of Na2CO3 and NaOH. Using Ph as indicator 25ml of mix required 19.5 ml of0.995 N HCl for the end point. With MeOH, 25 ml of the solution required 25ml of the same HCl for theend point. Calculate gms/L of each substance in the mix .

Q.47 200ml of a solution of mixture of NaOH and Na2CO3 was first titrated with Ph and10

N HCl. 17.5 ml of

HCl was required for end point. After this MeOH was added and 2.5 ml of some HCl was againrequired for next end point. Find out amounts of NaOH and Na2CO3 in the mix.

Q.48 A solution contains Na2CO3 and NaHCO3. 10ml of this requires 2ml of 0.1M H2SO4 for neutralisationusing Ph indicator. MeOH is then added when a further 2.5 ml of 0.2 M H2SO4 was needed. Calculatestrength of Na2CO3 and NaHCO3 in g/L.


Phone :- 9929617387 Fax :- 0744 - 2405300

Redox Titration

Q.49 It requires 40.05 ml of 1M Ce4+ to titrate 20ml of 1M Sn2+ to Sn4+. What is the oxidation state of thecerium in the product.

Q.50 A volume of 12.53 ml of 0.05093 M SeO2 reacted with exactly 25.52 ml of 0.1M CrSO4. In thereaction, Cr2+ was oxidized to Cr3+. To what oxidation state was selenium converted by the reaction.

Q.51 Potassium acid oxalate K2C2O4 · 3H2C2O4·4H2O can be oxidized by MnO4– in acid medium. Calculate

the volume of 0.1M KMnO4 reacting in acid solution with one gram of the acid oxalate.

Q.52 Metallic tin in the presence of HCI is oxidized by K2Cr2O7 to stannic chloride, SnCl4. What volume ofdeci-normal dichromate solution would be reduced by 1g of tin.

Q.53 5g sample of brass was dissolved in one litre dil. H2SO4. 20 ml of this solution were mixed with KI,liberating I2 and Cu+ and the I2 required 20 ml of 0.0327 N hypo solution for complete titration. Calculatethe percentage of Cu in the alloy.

Q.54 0.84 g iron ore containing x percent of iron was taken in a solution containing all the iron in ferrouscondition. The solution required x ml of a dichromatic solution for oxidizing the iron content toferric state. Calculate the strength of dichromatic solution.

Q.55 The neutralization of a solution of 1.2 g of a substance containing a mixture of H2C2O4. 2H2O, KHC2O4.H2O and different impurities of a neutral salt consumed 18.9 ml of 0.5 N NaOH solution. On titrationwith KMnO4 solution, 0.4 g of the same substance needed 21.55 ml of 0.25 N KMnO4. Calculate the% composition of the substance.

Back Titration

Q.56 50gm of a sample of Ca(OH)2 is dissolved in 50ml of 0.5N HCl solution. The excess of HCl was titratedwith 0.3N – NaOH. The volume of NaOH used was 20cc. Calculate % purity of Ca(OH)2.

Q.57 One gm of impure sodium carbonate is dissolved in water and the solution is made up to 250ml. To 50mlof this made up solution, 50ml of 0.1N – HCl is added and the mix after shaking well required 10ml of0.16N – NaOH solution for complete titration. Calculate the % purity of the sample.

Q.58 What amount of substance containing 60% NaCl, 37% KCl should be weighed out for analysis so thatafter the action of 25 ml of 0.1N AgNO3 solution, excess of Ag+ is back titrated with 5 ml of NH4SCNsolution? Given that 1 ml of NH4SCN = 1.1 ml of AgNO3.

Q.59 5g of pyrolusite (impure MnO2) were heated with conc. HCl and Cl2 evolved was passed through

excess of KI solution. The iodine liberated required 40 mL of10

Nhypo solution. Find the % of MnO2 in

the pyrolusite.


Phone :- 9929617387 Fax :- 0744 - 2405300

Eudiometry

Q.60 10 ml of a mixture of CO, CH4 and N2 exploded with excess of oxygen gave a contraction of 6.5 ml.There was a further contraction of 7 ml, when the residual gas treated with KOH. What is the compositionof the original mixture?

Q.61 When 100 ml of a O2 – O3 mixture was passed through turpentine, there was reduction of volume by 20ml. If 100 ml of such a mixture is heated, what will be the increase in volume?[Hint : O3 is absorbed by turpentine]

Q.62 10 ml of a gaseous organic compound containing C, H and O only was mixed with 100 ml of oxygen andexploded under conditions which allowed the water formed to condense. The volume of the gas afterexplosion was 90 ml. On treatment with potash solution, a further contraction of 20 ml in volume wasobserved. Given that the vapour density of the compound is 23, deduce the molecular formula. Allvolume measurements were carried out under the same conditions.

Q.63 A mixture of formic acid and oxalic acid is heated with concentrated H2SO4. The gas produced iscollected and on its treatment with KOH solution the volume of the gas decreased by one-sixth. Calculatethe molar ratio of the two acids in the original mixture.

Q.64 40 ml of a mixture of hydrogen, CH4 and N2 was exploded with 10 ml of oxygen. On cooling, the gasesoccupied 36.5 ml. After treatment with KOH the volume reduced by 3 ml and again on treatment withalkaline pyrogallol, the volume further decreased by 1.5 ml. Determine the composition of the mixture.

Q.65 5 ml of a gaseous hydrocarbon was exploded to 30 ml of O2. The resultant gas, on cooling is found tomeasure 25 ml of which 10 ml are absorbed by KOH and the remainder by pyragallal. Determinemolecular formula of hydrocarbon.


Phone :- 9929617387 Fax :- 0744 - 2405300

PROFICIENCY TEST

Q.1 Fill in the blanks with appropriate items :

1. The number of water molecules in 0.5 mol of barium chloride dihydrate is _________.

2. 20ml of 0.1 M H2C2O4 · 2H2O (oxalic acid) solution contains oxalic acid equal to _________ moles.

3. The volume of 1.204 × 1024 molecules of water at 4°C is _________.

4. 0.2 mol of ozone (O3) at N.T.P. will occupy volume _________ L.

5. The balancing of chemical equation is based upon _________.

6. 2 gm of hydrogen will have same number of H atoms as are there in ________ g hydrazine (NH2–NH2).

7. The mass of x atoms of element =AN

.........x.

8. The moles of x atoms of a triatomic gas =AN

x × _________.

9. The amount of Na2SO4 which gives 9.6 gm of 24SO is _________.

10. The 44 mg of certain substance contain 6.02 × 1020 molecules. The molecular mass of the substance is_________.

11. The mass of 1 ×1022 molecules of CuSO4. 5H2O is _________.

12. The atomic mass of iron is 56. The equivalent mass of the metal in FeCl2 is ___________ and that inFeCl3 is _________.

13. The sulphate of a metal M contains 9.87% of M. The sulphate is isomorphous with ZnSO4.7H2O. Theatomic mass of M is __________.

14. A binary compound contains 50% of A (at. mass = 16) & 50% B (at. mass = 32). The empirical formulaof the compound is _________.

15. 10.6 g of Na2CO3 react with 9.8 g of H2SO4 to form 16 g of Na2SO4 & 4.4 g CO2. This is inaccordance with the law of _________.

16. 3 g of a salt (m. wt. 30) are dissolved in 250 ml of water. The molarity of solution is _________.

17. 0.5 mole of BaCl2 are mixed with 0.2 mole of Na3PO4 the maximum number of mole of Ba3(PO4)2formed are __________.

18. The Eq. weight of Na2HPO4 (base) is ______________.


Phone :- 9929617387 Fax :- 0744 - 2405300

19. The mole fraction of solute in 20% (by weight) aqueous H2O2 solution is __________.

20. A metallic oxide contains 60% of the metal. The Eq. weight of the metal is __________.

21. The number of gm of anhydrous Na2CO3 present in 250 ml of 0.25 N solution is___________.

22. ________ ml of 0.1 M H2SO4 is required to neutralize 50 ml of 0.2 M NaOH solution.

23. The number of mole of water present in 90 g H2O are _________.

24. The concentration of K+ ion in 0.2 M K2Cr2O7 solution would be__________.

25. 280 ml of sulphur vapour at NTP weight 3.2 g . The Mol. formula of the sulphur vapour is ______.

Q.2 True or False Statements :

1. Equal volumes of helium and nitrogen under similar conditions have equal number of atoms.

2. The smallest particle is a substance which is capable in independent existence is called an atom.

3. The number of formula units in 0.5 mole of KCl is 6.02 × 1023.

4. 22.4 L of ethane gas at S.T.P. contains H atoms as are present in 3 gram molecules of dihydrogen.

5. Molarity of pure water is 55.5.

6. A 20% solution of KOH (density = 1.02 g/ml) has molarity = 3.64.

7. In a mixture of 1 g C6H6 & 1 g C7H8, the mole fraction of both are same.

8. 1 mole of C12H22O11 contains 22 hydrogen atoms.

9. KClO4 & KMnO4 are isomorphous in nature.

10. Mass of 3.01 × 1023 molecules of of methane is 8 gm.

11. A hydrocarbon contains 86% C. 448 ml of the hydrocarbon weighs 1.68 g at STP. Then the hydrocarbonis an alkene.

12. 6.023 × 1054 e–s weigh one kg.

13. An oxide of metal M has 40% by mass of oxygen. Metal M has relative atomic mass of 24. Theempirical formula of the oxide is MO.

14. 5 g of a crystalline salt when rendered anhydrous lost 1.8 g of water. The formula weight of the anhydroussalt is 160. The number of molecules of water of crystallisation in the salt is 5.


Phone :- 9929617387 Fax :- 0744 - 2405300

15. Number of valence e–s in 4.2 g of N 3– is 24 NA.

16. The equivalent mass of KMnO4 in alkaline medium is molar mass divided by five.

17. The equivalent mass of Na2S2O3 in its reaction with I2 is molar mass divided by two.

18. In a reaction, H2MoO4 is changed to MoO2+. In this case, H2MoO4 acts as an oxidising agent.

19. KBrO3 acts as a strong oxidising agent. It accepts 6 electrons to give KBr.

20. 0.1 M sulphuric acid has normality of 0.05 N.

21. The reaction, 2H2O2 2H2O + O2 is not an example of a redox reaction.

22. The disproportionation reaction,2Mn3+ + 2H2O MnO2 + Mn+2 + 4H+

is an example of a redox reaction.

23. The oxidation number of hydrogen is always taken as + 1 in its all compounds.

24. The increase in oxidation number of an element implies that the element has undergone reduction.

25. The oxidation state of oxygen atom in potassium super oxide is2

1 .


Phone :- 9929617387 Fax :- 0744 - 2405300

EXERCISE-II

Q.1 A sample of calcium carbonate contains impurities which do not react with a mineral acid. When 2 gramsof the sample were reacted with the mineral acid, 375 ml of carbon dioxide were obtained at 27°C and760 mm pressure. Calculate the % purity of the sample of CaCO3?

Q.2 One gram of an alloy of aluminium and magnesium when heated with excess of dil. HCl forms magnesiumchloride, aluminium chloride and hydrogen. The evolved hydrogen collected over mercury at 0°C has avolume of 1.2 litres at 0.92 atm pressure. Calculate the composition of the alloy.

Q.3 Chloride samples are prepared for analysis by using NaCl, KCl, NH4Cl separately or as mixtures. Whatminimum volume of a 5% (by weight) AgNO3 solution (sp. gr = 1.04) must be added to a sampleweighing 0.3 g in order to ensure complete precipitation of chloride in every possible case?

Q.4 Sulfur dioxide is an atmospheric pollutant that is converted to sulfuric acid when it reacts with watervapour. This is one source of acid rain, one of our most pressing environmental problems. The sulfurdioxide content of an air sample can be determined as follows. A sample of air is bubbled through anaqueous solution of hydrogen peroxide to convert all of the SO2 to H2SO4

H2O2 + SO2 H2SO4Titration of the resulting solution completes the analysis. In one such case, analysis of 1550 L of LosAngeles air gave a solution that required 5.70 ml of 5.96 × 10–3M NaOH to complete the titration.Determine the number of grams of SO2 present in the air sample.

Q.5 In a water treatment plant, Cl2 used for the treatment of water is produced from the following reaction2KMnO4 + 16 HCl 2KCl + 2MnCl2 + 8H2O + Cl2. If during each feed 1 l KMnO4 having 79%(w/v) KMnO4 & 9 l HCl with d = 1.825 gm/ ml & 10% (w/w) HCl are entered & if that percent yieldis 80% then calculate

(a) amount of Cl2 produced.(b) amount of water that can be treated by Cl2 if 1 litres consumes 28.4 g of Cl2 for treatment.

(c) Calculate efficiency of the process if = feedtotalofvol

treatedwaterof.vol

Q.6 A 2.0 g sample of a mixture containing sodium carbonate, sodium bicarbonate and sodium sulphate isheated till the evolution of CO2 ceases. The volume of CO2 at 750 mmHg pressure and at 298 K ismeasured to be 123.9 mL. A 1.5 g of the sample requires 150 mL of M /10 HCl for complete neutralization.Calculate the percentage composition of the components of the mixture.

Q.7 3.6 g of Mg is burnt in limited supply of oxygen. The residue was treated with 100 mL of H2SO4(35% by mass,1.26 g mL–1 density). When 2.463 L of H2 at 760 mm Hg at 27°C was evolved. Afterthe reaction, H2SO4 was found to have a density of 1.05 g mL–1. Assuming no volume change inH2SO4 solution. Find(i) % by mass of final H2SO4(ii) % by mass of Mg converted to oxide(iii) mass of oxygen used. (Mg = 24, S= 32)


Phone :- 9929617387 Fax :- 0744 - 2405300

Q.8 One mole of a mixture of N2, NO2 and N2O4 has a mean molar mass of 55.4. On heating to a temperatureat which all the N2O4 may be pressured to have dissociated : N2O4 2NO2, the mean molar masstends to the lower value of 39.6. What is the mole ratio of N2 : NO2 : N2O4 in the original mixture?

Q.9 A mixture of FeO and Fe2O3 is reacted with acidified KMnO4 solution having a concentration of 0.2278M, 100 ml of which was used. The solution was then titrated with Zn dust which converted Fe3+ of thesolution to Fe2+. The Fe2+ required 1000 ml of 0.13 M K2Cr2O7 solution. Find the % of FeO & Fe2O3.

Q.10 50ml of a solution, containing 1gm each Na2CO3, NaHCO3 and NaOH was titrated with N-HCl. Whatwill be the titre readings if(a) only Ph is used as indicator.(b) only MeOH is used as indicator from the beginning.(c) MeOH is added after the first end point with Ph.

Q.11 A 0.517g sample containing Ba(SCN)2 was dissolved in a bicarbonate solution. 50.0 mL of 0.107 Niodine was added, and the mixture was allowed to stand for five minutes. The solution was then acidified,and the excess I2 was titrated with 16.3 mL of 0.0965 M sodium thiosulphate. Calculate the percentBa(SCN)2 in the sample.

Q.12 A mixture of Xe and F2 was heated. A sample of white solid thus formed reacted with H2, to give 81 mlof Xe at STP and HF formed required 68.43 ml of 0.3172 M NaOH for complete neutralization.Determine empirical formula.

Q.13 Chrome alum K2SO4 . Cr2(SO4)3 . 24 H2O is prepared by passing SO2 gas through an aqueoussolution of K2Cr2O7 acidified with dilute sulphuric acid till the reduction is complete. The alum iscrystallized followed by filtration/centrifugation. If only 90% of the alum can be recovered from theabove process, how much alum can be prepared from 10kg of K2Cr2O7? Give the number of moles ofelectrons supplied by SO2 for reducing one mole of K2Cr2O7.

Q.14 A substance of crude copper is boiled in H2SO4 till all the copper has reacted. The impurities are inertto the acid. The SO2 liberated in the reaction is passed into 100 mL of 0.4 M acidified KMnO4. Thesolution of KMnO4 after passage of SO2 is allowed to react with oxalic acid and requires 23.6 mL of1.2 M oxalic acid. If the purity of copper is 91%, what was the weight of the sample.

Q.15 25 mL of a solution containing HCl was treated with excess of M/5 KIO3 and KI solution of unknownconcentration where I2 liberated is titrated against a standard solution of 0.021M Na2S2O3 solutionwhose 24 mL were used up. Find the strength of HCl and volume of KIO3 solution consumed.

Q.16 A 10g sample of only CuS and Cu2S was treated with 100 mL of 1.25 M K2Cr2O7. The productsobtained were Cr3+, Cu2+ and SO2. The excess oxidant was reacted with 50 mL of Fe2+ solution. 25 mlof the same Fe2+ solution required 0.875M acidic KMnO4 the volume of which used was 20 mL. Findthe % of CuS and Cu2S in the sample.

Q.17 H2O2 is reduced rapidly by Sn2+, the products being Sn4+ & water. H2O2 decomposes slowly at roomtemperature to yield O2 & water. Calculate the volume of O2 produced at 20C & 1.00 atm when 200gof 10.0 % by mass H2O2 in water is treated with 100.0 ml of 2.00 M Sn2+ & then the mixture is allowedto stand until no further reaction occurs.


Phone :- 9929617387 Fax :- 0744 - 2405300

Q.18 A sample of steel weighing 0.6 gm and containing S as an impurity was burnt in a stream of O2, when Swas converted to its oxide SO2. SO2 was then oxidized to SO4

– – by using H2O2 solution containing30ml of 0.04 M NaOH. 22.48 ml of 0.024 M HCl was required to neutralize the base remaining afteroxidation. Calculate the % of S in the sample.

Q.19 CuFeS2 mineral was analysed for Cu and Fe percentage. 10g of it was boiled with dil. H2SO4 anddiluted to 1L. 10 mL of this solution required 2mL of 0.01M MnO4

in acidic medium. In anothertitration 25 mL of the same solution required 5 mL of 0.01M S2O3

2 solution iodometrically. Calculatepercentage of Cu and Fe in the mineral.

Q.20 A 10gm mixture of Cu2S and CuS was treated with 200 ml of 0.75 M MnO4– in acid solution, producing

SO2, Cu2+ & Mn2+. The SO2 was boiled off and the excess MnO4– was titrated with 175 ml of 1M

Fe2+ solution. Calculate the % CuS in the original mixture.

Q.21 3.3 gm of a sample of Anhydrous CuSO4 was dissolved in water and made to 250ml. 25 ml of thissolution after taking usual precautions was treated with a little excess of KI solution. A white ppt. ofCu2I2 and iodine was evolved. The iodine so evolved required 24.6 ml of hypo solution containing 20gmof (Na2S2O3 · 5H2O) per litre. What is the purity of CuSO4 solution.

Q.22 1.16 g CH3(CH2)n COOH was burnt in excess air and the resultant gases (CO2 and H2O) were passedthrough excess NaOH solution. The resulting solution was divided in two equl parts. One part requires50 mL of 1 N HCl for neutralization using phenolphthalein as indicator. Another part required 80 mL of1N HCl for neutralization using methyl orange as indicator. Find the value of n and the amount of excessNaOH solution taken initially.

Q.23 A 1.65 gm sample of FeS2 was oxidized by excess oxygen & the products were SO2 and Fe2+. TheSO2 gas produced was passed through an acidified solution of 40ml Ba(MnO4)2 produced SO4

– – &Mn2+. The excess permagnate was diluted to 100 ml & 10 ml of it was treated with excess KI & iodineproduced req. 0.05 M 5 ml hypo solution producing S4O6

2–. In a separate titration the 25 ml of samesolution of permagnate under alkaline condition when treated with KI produced I2 that required 20 ml of0.05 M hypo solution producing S4O6

2– & Mn6+. Calculate the % of FeS2 in the sample.Q.24 Reducing sugars are sometimes characterized by a number RCu, which is defined as the number of mg of

copper reduced by 1 gm of sugar, in which half reaction for the copper isCu2+ + OH– Cu2O + H2O

It is sometimes more convenient to determine the reducing power of a carbohydrate by an indirectmethod. In this method 43.2 mg of the carbohydrate was oxidized by an excess of K3(Fe(CN)6). TheFe(CN)6

4– formed in this reaction required 5.29 ml of 0.0345 N Ce(SO4)2 for reoxidation to Fe(CN)63.

Determine the RCu value for the sample.

Q.25 2g of chromite ore sample was mixed with enough potassium carbonate and potassium chlorate andfused. The reaction that occurred was:

6FeCr2O4 + 12K2CO3 + 7KCIO3 3Fe2O3 + 12 K2CrO4 + 7KCl + 12CO2The fused mass was cooled and extracted with 2N sulphuric acid. This was filtered and thoroughlywashed. The filterate and washings were collected in a 500 ml. Volumetric flask. When all the solubleportion of the fused mass was extracted, 100 ml of 1M solution of ferrous ammonium sulphate wereadded and the solution made to 500ml. An aliquot of 25ml was titrated with potassium dichromatesolution, prepared by dissolving 0.98 g of dried potassium dichromate in distilled water in a 250mlvolumetric flask. The titration required 32.5 ml of this solution. Calculate the percentage of chromium inthe sample of the ore.


Phone :- 9929617387 Fax :- 0744 - 2405300

EXERCISE-III

Q.1 Which has maximum number of atoms of oxygen(A) 10 ml H2O(l) (B) 0.1 mole of V2O5(C) 12 gm O3(g) (D) 12.044 ×1022 molecules of CO2

Q.2 Mass of one atom of the element A is 3.9854 × 10–23g. How many atoms are contained in1 g of the element A?(A) 2.509 × 1023 (B) 6.022 × 1023 (C) 12.044 ×1023 (D) None

Q.3 The total no. of electrons present in 11.2 litre of NH3 at STP are(A) 6.022 × 1023 (B) 3.011 × 1023 (C) 3.011 × 1024 (D) None

Q.4 1 gm-atom of nitrogen represents :(A) 6.02 × 1023 N2 molecules (B) 22.4 lit. of N2 at N.T.P.(C) 11.2 lit. of N2 at N.T.P. (D) 28 g of nitrogen

Q.5 Al2(SO4)3. x H2O has 8.20 % aluminium by mass. The value of x is(A) 4 (B) 10 (C) 16 (D) 18

Q.6 If average molecular wt. of air is 29, then assuming only N2 and O2 gases are there which options arecorrect regarding composition of air(i) 75% by mass of N2(ii) 75% by moles N2(iii) 72.41% by mass N2(A) only (i) is correct (B) only (ii) is correct(C) both (ii) and (iii) are correct (D) both (i) and (ii) are correct

Q.7 A spherical ball of radius 3 cm contains 66.66 % iron. If density is 1.5 g/cm3, number of mole of Fepresent approximately is:(A) 1 (B) 2 (C) 20 (D) None

Q.8 Density of dry air containing only N2 and O2 is 1.146 gm/lit at 740 mm and 300 K. What is % compositionof N2 by weight in the air.(A) 78% (B) 82% (C) 73.47% (D) 72.42%

Q.9 What is the number of moles of Fe(OH)3 that can be produced by allowing1 mole of Fe2S3, 2 mole of H2O and 3 mole of O2 to react2Fe2S3 + 6H2O + 3O2 4Fe(OH)3 + 6S(A) 2 (B) 1.34 (C) 3.52 (D) none

Q.10 What percentage of phosphorus (P) is present in the compound CaCO3. 3Ca3(PO4)2?(A) 18% (B) 45.36% (C) 28.61% (D) 15.12%

Q.11 A gaseous mixture of H2 and NH3 gas contains 68 mass % of NH3. The vapour density of the mixture is(A) 6.1 (B) 5 (C) 2.5 (D) None of these

Q.12 A sample of ammonium phosphate, (NH4)3 PO4, contains 3.18 mol of hydrogen atoms.The number ofmoles of oxygen atoms in the sample is :(A) 0.265 (B) 0.795 (C) 1.06 (D) 3.18


Phone :- 9929617387 Fax :- 0744 - 2405300

Q.13 12 litre of H2 and 11.2 litre of Cl2 are mixed and exploded. The composition by volume of mixture is(A) 24 litre of HCl (B) 0.8 litre Cl2 and 20.8 lit HCl(C) 0.8 litre H2 & 22.4 litre HCl (D) 22.4 litre HCl

Q.14 Weight of oxygen in Fe2O3 and FeO is in the simple ratio for the same amount of iron is(A) 3 : 2 (B) 1 : 2 (C) 2 : 1 (D) 3 : 1

Q.15 A mixture of gas ''X'' (mol. wt. 16) and gas Y (mol. wt. 28) in the mole ratio a : b has a mean molecularweight 20. What would be mean molecular weight if the gases are mixed in the ratio b : a under identicalconditions (gases are non reacting).(A) 24 (B) 20 (C) 26 (D) 40

Q.16 A mixture of CuO and Cu2O contain 88% Cu. What is the percentage of CuO present in the mixture?(A) 91.35% (B) 8.89% (C) 18.9% (D) 20%

Q.17 Consider the following nuclear reactions involving X & Y.

X Y + He42

Y 8O18 + 1H

1

If both neutrons as well as protons in both the sides are conserved in nuclear reaction then identifyperiod number of X & moles of neutrons in 4.6 gm of X(A) 3, 2.4 NA (B) 3, 2.4 (C) 2, 4.6 (D) 3, 0.2 NA

Q.18 To 500 ml of 2 M impure H2SO4 sample, NaOH solution 1 M wasslowly added & the following plot was obtained. The percentagepurity of H2SO4 sample and slope of the curve respectively are:

(A) 50%,3

1 (B) 75%,

2

1

(C) 75% , –1 (D) none of these

Q.19 Equal volumes of 10% (v/V) of HCl is mixed with 10% (v/V) NaOH solution. If density of pure NaOHis 1.5 times that of pure HCl then the resultant solution be.(A) basic (B) neutral (C) acidic (D) can’t be predicted.

Q.20 The mole fraction of a given sample of I2 in C6H6 is 0.2. The molality of I2 in C6H6 is(A) 0.32 (B) 3.2 (C) 0.032 (D) 0.48

Q.21 A sample of H2SO4 (density 1.8 g/ml) is 90% by weight. What is the volume of the acid that has to beused to make 1 litre of 0.2 –M H2SO4 ?(A) 16 mL (B) 10 mL (C) 12 mL (D) 18 mL

Q.22 What volume of HNO3 (sp. gravity 1.05 g ml–1 containing 9%(w/w) of HNO3 reducing to NOg ) isrequired to oxidise iron 1 g FeSO4. 7H2O in acid medium is(A) 70 ml (B) 0.80 ml (C) 80 ml (D) 0.65 ml

Q.23 One litre of a sample of hard water contain 2.22 mg CaCl2 and 1.9 mg of MgCl2 in 1 L H2O. What is thetotal hardness in terms of ppm of CaCO3. [Ca = 40; Mg = 24, Cl = 35.5](A) 2 ppm (B) 3 ppm (C) 4 ppm (D) 4.12 ppm


Phone :- 9929617387 Fax :- 0744 - 2405300

Q.24 10 L of hard water required 0.56 gm of lime for removing hardness. Hence temporary hardness in ppmof CaCO3 is(A) 100 (B) 200 (C) 10 (D) 20

Q.25 0.1 gm of a polyvalent metal of atomic mass 51.0 amu reacted with dilute sulphuric acid to give 43.9 mlof H2 at STP. The solution in the lower oxidation state was found to require 58.8 ml ofN/10 KMnO4 solution for complete oxidation. The valencies of the metal is(A) M2+ and M5+ (B) M3+ and M6+ (C) M1+ and M5+ (D) M2+ and M3+

Q.26 Equivalent weight of H3PO2 when it disproportionate into PH3 and H3PO3 is(A) M (B) M/2 (C) M/4 (D) 3M/4

Q.27 A mixture of NaHC2O4 and KHC2O4 · H2C2O4 required equal volumes of 0.2 N KMnO4 and0.12 N NaOH separately. What is the molar ratio of NaHC2O4 and KHC2O4 · H2C2O4 in the mixture?(A) 6 : 1 (B) 1 : 6 (C) 1 : 3 (D) none

Q.28 100 cm3 of a solution of an acid (Molar mass = 82) containing 39 gm of the acid per litre were completelyneutralized by 95.0 cm3 of aq. NaOH containing 20 gm of NaOH per 500 cm3. The basicity of the acid is(A) 1 (B) 2 (C) 3 (D) data insufficient

Q.29 Which of the following is correct for 17 g/L of H2O2 solution.(I) Volume strength is 5.6 at 273 K and 1 atm(II) Molarity of solution is 0.5 M(III) 1 ml of this solution gives 2.8 ml O2 at 273 K and 2 atm(IV) The normality of solution is 2M(A) I, II, III (B) II, III (C) II, III, IV (D) I, II, III, IV

Q.30 In iodometric estimation of Cu2+ ion, the following reaction took place.2Cu2+ + 4I– — Cu2I2 + I2

I2 + 2Na2S2O3 — 2NaI + Na2S4O6If 100 ml of CuSO4 solution added to excess KI requires 50 ml of 0.2 M Na2S2O3, the molarity ofCuSO4 solution is(A) 0.05 M (B) 0.1 M (C) 0.2 (D) 0.25

Q.31 500 ml of a sample of H2O2 marked 33.6 volumes is used as source of oxygen. This sample partlyreacted with certain reactive impurities causing wastage of half the amount of H2O2 present. Volume ofO2 available at 570 mm Hg & 27°C is:(A) 12.3 L (B) 24.6 L (C) 16.8 L (D) none of these

Q.32 Calculate the mass of anhydrous oxalic acid, which can be oxidised to CO2(g) by 100 ml of an4MnO solution, 10 ml of which is capable of oxidising 50 ml of 1N I– to I2.

(A) 45 gm (B) 22.5 gm (C) 30 gm (D) 12.25 gm


Phone :- 9929617387 Fax :- 0744 - 2405300

Q.33 Three different solutions of oxidising agents KMnO4, K2Cr2O7 and I2 is titrated seperately with 0.158 gmof Na2S2O3. If molarity of each oxidising agent is 0.1 M and reactions are

4MnO + 2

32OS MnO2 +2

4SO

272OCr + 2

32OS Cr3+ + 24SO

I2 + Na2S2O3 Starch Na2S4O6 + I–

Then(A) volume of KMnO4 used is maximum (B) volume of K2Cr2O7 used is minimum(C) wt. of I2 used in titration is maximum (D) none

Q.34 Find out % of oxalate ion in a given sample of an alkali metal oxalate salt, 0.30 gm of it is dissolved in100 CC water required 90 CC of centimolar KMnO4 solution in acidic medium.(A) 66% (B) 55% (C) 44% (D) 88%

Q.35 1 gram at a sample of CaCO3 was strongly heated and the CO2 liberated was absorbed in 100 mL of0.5 M NaOH. Assuming 90% purity for the sample. How much mL of 0.5 M HCl would be required toreact with the solution of the alkali to reach the phenolphthalein end point?(A) 73 mL (B) 41 mL (C) 82 mL (D) 87 mL

Q.36 A 0.518 g sample of lime stone is dissolved in HCl and then the calcium is precipitated as CaC2O4. Afterfiltering and washing the precipitate, it requires 40.0 mL of 0.250 N KMnO4, solution acidified withH2SO4 to titrate it as,

4MnO + H+ + 2

42OC Mn2+ + CO2 + 2H2O

The percentage of CaO in the sample is:(A) 54.0% (B) 27.1% (C) 42% (D) 84%

Q.37 0.3 g of an oxalate salt was dissolved in 100 mL solution. The solution required 90 mL of N/20 KMnO4for complete oxidation. The % of oxalalte ion in salt is:(A) 33% (B) 66% (C) 70% (D) 40%

Q.38 A sample of H2O2 solution labelled as 33.6 volume has density of 264 gm/lit. Mark the correct optionrepresenting concentration of same solution in other units. [Solution contains only H2O & H2O2](A) Mole fraction of H2O2 in the solution = 0.5(B) % w/v = 102%

(C)22OHM = 6 M

(D)22OHm =

54

1000m

Q.39 Match the n-factor of following reactant :(i) As2S3 AsO4

3– + SO42– (half reaction) (a) 10

(ii) Bi2S3 Bi+5 + S (half reaction) (b) 4(iii) Mn(NO3)2 MnO4

2– + NO3– (half reaction) (c) 2/3

(iv) 5P2H4 6PH3 + P4H2 (d) 6/5(v) MnO4

2– + H2O MnO2 + MnO4– + OH– (e) 28

(A) (i)-(a), (ii)-(b), (iii)-(c), (iv)-(d), (v)-(e) (B) (i)-(c), (ii)-(a), (iii)-(b), (iv)-(d), (v)-(e)(C) (i)-(e), (ii)-(a), (iii)-(b), (iv)-(d), (v)-(c) (D) (i)-(e), (ii)-(b), (iii)-(a), (iv)-(c), (v)-(d)


Phone :- 9929617387 Fax :- 0744 - 2405300

Question No. 40 to 43 (4 questions)A 4.925 g sample of a mixture of CuCl2 and CuBr2 was dissolved in water and mixed thoroughly with a5.74 g portion of AgCl. After the reaction the solid, a mixture of AgCl and AgBr, was filtered, washed,and dried. Its mass was found to be 6.63 g.

Q.40 % By mass of CuBr2 in original mixture is(A) 2.24 (B) 74.5 (C) 45.3 (D) None

Q.41 % By mass of Cu in original mixture is(A) 38.68 (B) 19.05 (C) 3.86 (D) None

Q.42 % by mole of AgBr in dried precipate is(A) 25 (B) 50 (C) 75 (D) 60

Q.43 No. of moles of Cl– ion present in the solution after precipitation are(A) 0.06 (B) 0.02 (C) 0.04 (D) None

Question No. 44 to 46 (3 questions)NaBr, used to produce AgBr for use in photography can be self prepared as follows :

Fe + Br2 FeBr2 ....(i)FeBr2 + Br2 Fe3Br8 ....(ii) (not balanced)Fe3Br8 + Na2CO3 NaBr + CO2 + Fe3O4 ....(iii) (not balanced)

Q.44 Mass of iron required to produce 2.06 × 103 kg NaBr(A) 420 gm (B) 420 kg (C) 4.2 × 105 kg (D) 4.2 × 108 gm

Q.45 If the yield of (ii) is 60% & (iii) reaction is 70% then mass of iron required to produce 2.06 × 103 kgNaBr(A) 105 kg (B) 105 gm (C) 103 kg (D) None

Q.46 If yield of (iii) reaction is 90% then mole of CO2 formed when 2.06 × 103 gm NaBr is formed(A) 20 (B) 10 (C) 40 (D) None

Question No. 47 and 48 are based on the following piece of information. Mark the appropriateoptions on the basis of information.342 gm of 20% by mass of Ba(OH)2 solution (sp. gr. 0.57) is reacted with 200 ml of 2M HNO3according to given balanced reaction.

Ba(OH)2 + 2HNO3 Ba(NO3)2 + 2H2OQ.47 The nature of the final solution is

(A) acidic (B) neutral (C) basic (D) can't sayQ.48 If density of final solution is 1.01 gm /ml then find the molarity of the ion in resulting solution by which

nature of the above solution is identified, is(A) 0.5 M (B) 0.8 M (C) 0.4 M (D) 1 M

Question No. 49 to 50 (2 questions)In the gravimetric determination of sulfur the ignited precipitate of BaSO4 sometimes partially reduces toBaS. This cause an error, of course, if the analyst does not realize this and thinks entire precipitate asBaSO4. Suppose a sample which contains 32.3% SO3 is analyzed and 20.0% of the final precipitatethat is weighed is BaS. (80.0% is BaSO4).

Q.49 Calculate the mass of sample, assuming 100 gm precipitate is formed(A) 106.3 gm (B) 114.35 gm (C) 110.5 gm (D) None

Q.50 Percentage of SO3 in the sample, calculated by analyst is (if the assume the entire 100 gm precipiate asBaSO4)(A) 30 (B) 30.5 (C) 32 (D) 32.3


Phone :- 9929617387 Fax :- 0744 - 2405300

EXERCISE-IV

Q.1 The number of moles of KMnO4 that will be needed to react with one mole of sulphite ions in acidicsolution is [JEE 1997 ](A) 2/5 (B) 3/5 (C) 4/5 (D) 1

Q.2 The normality of 0.3 M phosphorus acid (H3PO3) is [JEE 1999 ](A) 0.1 (B) 0.9 (C) 0.3 (D) 0.6

Q.3 One mole of calciums phosphide on reaction with excess of water gives [JEE 1999 ](A) one mole of phosphine (B) Two moles of phsophoric acid(C) Two moles of phosphine (D) One mole of phosphorus pentoxide

Q.4 An aqueous solution of 6.3 gm of oxalic acid dihydrate is made upto 250 ml. The volume of 0.1 NNaOH required to completely neutralize 10 ml of this solution is [JEE 2001 ](A) 40 ml (B) 20 ml (C) 10 ml (D) 4 ml

Q.5 In the standarization of Na2S2O3 using K2Cr2O7 by iodometry the equivalent mass of K2Cr2O7 is

(A)2

Mass.M(B)

6

Mass.M(C)

3

Mass.M(D) Same as M. Mass.

[JEE 2001 ]Q.6 How many moles of electrons weigh one kilogram

(A) 6.02 × 1023 (B)108.9

1 × 1031 (C)

108.9

023.6 × 1054 (D)

02.6

10

108.9

1 8

[JEE 2002 ]

Q.7 Which has maximum number of atoms? [JEE 2003 ](A) 24 g C (12) (B) 56 g Fe (56) (C) 27g Al (27) (D) 108 g Ag (108)

SUBJECTIVES

Q.8 One litre of a mixture of O2 and O3 at NTP was allowed to react with an excess of acidified solution ofKI. The iodine liberated required 40 ml of M/10 sodium thiosulphate solution for titration. What is thepercent of ozone in the mixture? Ultraviolet radiation of wavelength 300 nm can decompose ozone.Assuming that one photon can decompose one ozone molecule, how many photons would have beenrequired for the complete decomposition of ozone in the original mixture? [ JEE’97, 5 ]

Q.9 A sample of hard water contains 96 ppm of 24SO and 183 ppm of

3HCO , with Ca2+ as the only

cation. How many moles of CaO will be required to remove 3HCO from 1000 kg of this water? If

1000 kg of this water is treated with the amount of CaO calculate above, what will be the conentration(in ppm) of residual Ca2+ ions (Assume CaCO3 to be completely insoluble in water)? If the Ca2+ ions inone litre of the treated water are completely exchanged with hydrogen ions, what will be its pH (one ppmmeans one part of the substance in one million part of water, weight/ weights)? [JEE’ 1997]

Q.10 An aqueous solution containing 0.10g KIO3 (formula wt. = 214.0) was treated with an excess of KIsolution. The solution was acidified with HCl. The liberated I2 consumed 45.0 ml of thiosulphate solutionto decolourise the blue starch iodine complex. Calculate the molarity of the sodium thiosulphatesolution. [ JEE’ 1998]


Phone :- 9929617387 Fax :- 0744 - 2405300

Q.11 How many millilitre of 0.5 M H2SO4 are needed to dissolve 0.5 gm of copper II carbonate?[JEE’ 1999]

Q.12 A plant virus is found to consist of uniform cylindrical particles of 150Å in diameter and 5000Å long. Thespecific volume of the virus is 0.75 cm3/gm. If the virus is considered to be a single particle, find itsmolecular weight. [JEE’ 1999]

Q.13 Hydrogen peroxide solution (20 mL) reacts quantitatively with a solution of KMnO4 (20 mL) acidifiedwith dilute H2SO4. The same volume of the KMnO4 solution is just decolorized by 10mL of MnSO4 inneutral medium simultaneously forming a dark brown precipitate of hydrated MnO2. The brown precipitateis dissolved in 10mL of 0.2M sodium oxalate under boiling condition in the presence of dilute H2SO4.Write the balanced equations involved in the reactions and calculate the molarity of H2O2.

[JEE’ 2001]

Q.14 Calculate the molarity of water if its density is 1000 kg/m3. [JEE’ 2003]

Q.15 1 gm charcoal is placed in 100 ml of 0.5 M CH3COOH to form an adsorbed mono-layer of acetic acidmolecule and thereby the molarity of CH3COOH reduces to 0.49. Calculate the surface area of charcoaladsorbed by each molecule of acetic acid. Surface area of charcoal = 3.01 × 102 m2/g. [JEE’ 2003]

Q.16 20% of surface sites are occupied by N2 molecules. Number of surface sites per unit area is

6.023 × 1014 cm–2 and total area of catalyst surface is 1000 cm2 . Now when catalyst is heatedto300K N

2 gas desorbed and evolved gas occupied, 2.46 cm3 at 0.001 atm. Find the no. of

sitesocupied by each molecule of N2. [JEE 2005]


Phone :- 9929617387 Fax :- 0744 - 2405300

ANSWER KEYEXERCISE-I

Q.1 1.33 × 1021 Q.2 2.4 L Q.3 166.6 ml Q.4 y atoms

Q.5 33.9 Q.6 4.44×1022 Q.7 0.05, 0.027 Q.8 2.22g ; 0.948g

Q.9 0.532 : 1 Q.10 9.063 gm Q.11 0.250 Q.12 1.14 g

Q.13 B105 =80%; B11

5 = 20% Q.14 C5H14N2 Q.15 C3H6O; C6H12O2

Q.16 108 Ag, 1.41 gm Q.17 41 Q.18 108.16 Q.19 At. wt. of Y = 70 amu

Q.20 29.29% Q.21 35.77% Q.22 (a) 26.25%, (b) 11.46%

Q.23 4.9 ml Q.24 1.03 gm Q.25 4.02%, 53.35%

Q.26 21.68% Q.27 %NaHCO3 = 16.8, % Na2CO3= 83.2

Q.28 67.9% Q.29 1.445 M Q.30 1.088 M, 1.13 m

Q.31 13.15 M Q.32 16.67% Q.33 2.7 × 10–4 m Q.34 1736.1 ml

Q.35 1.71 M Q.36 15.96 m Q.37 0.1N Q.38 1 : 2

Q.39 (a) 1.2 M ; (b) 9.18 × 10–3; (c) 1.2 × 104 ppm

Q.40 V = 157.8 ml Q.41 20.72 % Q.42 200 mL

Q.43 MgCO3 = 52.02%, CaCO3 = 47.98 %

Q.44 83.33 Q.45 0.424 gm; 0.21gm Q.46 23.2 gm, 22.28gm

Q.47 0.06gm; .0265gm Q.48 4.24 g/L; 5.04 g/L Q.49 + 3

Q.50 zero Q.51 V = 31.68 ml Q.52 337 mL Q.53 41.53%

Q.54 0.15 N Q.55 H2C2O4. 2H2O = 14.35%, KHC2O4. H2O = 81.71%

Q.56 1.406% Q.57 90.1% Q.58 0.1281 g Q.59 0.174g; 3.48%

Q.60 CO = 5 ml ; CH4 = 2 ml ; N2 = 3 ml Q.61 10 ml

Q.62 C2H6O Q.63 4 :1 \

Q.64 H2 : 12.50%, CH4: 7.50%, N2 : 80% Q.65 C2H4

PROFICIENCY TESTQ.11. 6.02 × 1023 2. 2 × 10–3 mol 3. 36 ml 4. 4.48 L

5. Laws of conservation of mass 6. 16 gm 7. GAM

8. 3 9. 14.2 gm 10. 44 g mol–1 11. 4.13 g

12. 44.8 L 13. 24.3 14. A2B 15. Conservation of mass

16. 0.4 17. 0.1 18. M/2 19. 0.1168

20. 12 21. 3.3125 g 22. 50 23. 5

24. 0.4 M 25. S8

Q.2

1. False 2. False 3. False 4. True


Phone :- 9929617387 Fax :- 0744 - 2405300

5. True 6. True 7. False 8. False

9. True 10. True 11. True 12. False

13. True 14. True 15. False 16. False

17. False 18. True 19. True 20. False

21. False 22. True 23. False 24. False

25. TrueEXERCISE-II

Q.1 76.15% Q.2 Al = 0.566 g; Mg = 0.434 g Q.3 18.33

Q.4 1.09 × 10–3 gm Q.5 (a)10 mol, (b) 25 lit., (c) 2.5

Q.6 NaHCO3= 42%, Na2CO3 = 26.5%, Na2SO4 = 31.5%

Q.7 (i) 28%, (ii) 33.33%, (iii) 0.8g Q.8 0.5 : 0.1 : 0.4

Q.9 FeO = 13.34%; Fe2O

3 = 86.66% Q.10 34.4 ml; 55.8 ml; 21.3 ml

Q.11 15.4% Q.12 XeF6 Q.13 30.55kg, 6 electrons

Q.14 5g Q.15 VKIO3 = 0.42 mL, [HCl] = 0.02N

Q.16 57.4% CuS, 42.6% Cu2S Q.17 4.67L Q.18 1.75%

Q.19 Fe = 5.6%, Cu = 1.27% Q.20 CuS = 57.9% Q.21 95.15%

Q.22 n = 4, NaOH = 6.4 g Q.23 10%

Q.24 RCu

= 269 Q.25 41.6%

EXERCISE-III

Q.1 C Q.2 D Q.3 C Q.4 C Q.5 D Q.6 C Q.7 BQ.8 D Q.9 B Q.10 A Q.11 C Q.12 C Q.13 C Q.14 AQ.15 A,D Q.16 B Q.17 B Q.18 C Q.19 A Q.20 B Q.21 CQ.22 B Q.23 C Q.24 A Q.25 A Q.26 D Q.27 D Q.28 BQ.29 A Q.30 B Q.31 A Q.32 B Q.33 A Q.34 A Q.35 CQ.36 A Q.37 B Q.38 D Q.39 C Q.40 C Q.41 A Q.42 DQ.43 A Q.44 B Q.45 C Q.46 B Q.47 C Q.48 A Q.49 BQ.50 A

EXERCISE-IV

Q.1 A Q.2 D Q.3 C Q.4 A Q.5 B Q.6 D Q.7 A

SUBJECTIVES

Q.8 6.57% O3(by weight), 1.2 × 1021 photons Q.9 1.5, 40 ppm, pH = 2.6989

Q.10 0.0623M Q.11 8.097 ml Q.12 7.095 × 107

Q.13 0.1M Q.14 55.55 Q.15 5 × 10–19 m2 Q.16 2

STOICHIOMETRY

Documents

Transcript of STOICHIOMETRY