Topic 9: Acids & Bgseg Outline 1. An electrolyte is a substance which when dissolved in water forms a solution capable of conducting an electric current The ability of a solution to conduct an electric current depends upon the concentration of /o/is present

I on i c c o m p o u n d s a r e conductors of e lectr ic i ty w h e n me l ted OR d isso lved in wa te r . Under these c i r cums t ances , the charged part ic les ( i ons in th is c a s e ) a re f ree to m o v e (mob i l e ) . T h e r e a re 3 ca tegor ies of e lec t ro ly tes : a c ids , b a s e s and sa l t s . A r rhen ius theory s t a t es that a n acid is a n s u b s t a n c e tha t d isso lves in wa te r to produce H* (H3O*) ions ( ca l led " h y d r o n i u m " ions on T a b l e E ) . A r rhen ius theory s t a t es that a base is an s u b s t a n c e tha t d isso lves in wa t e r to produce OH" ions ( ca l led " h y d r o x i d e " ions on T a b l e E ) . A sa l t is a n y ionic compound produc ing a pos i t ive ion other than H* and a negat ive ion other t h a n 0H- . C o m m o n ac id a n d base n a m e s and fo rmu las a r e g i ven on T a b l e s K a n d L. you sfmuld be ab/e to sort cofwounds as acicA bases or salts, given tt]eir cfiemica/ lorrrtuiss

2. Properties of many acids and bases can be explained by the Arrhenius theory. Arrhenius acids and bases are electrolytes.

Acid proper t ies include sour t a s te , less than 7 pH, abil i ty to neutra l ize ba se s , and abil i ty to a f fec t indicator co lors . T h e s e proper t ies are due to the H* ion. Base proper t ies inc lude bitter t a s te , g rea te r t h a n 7 pH, ability to neut ra l ize ac ids , and abil ity to af fec t ind icator co lors . T h e s e propert ies a re due to the O H ' ion. lUien g/Veo properties, you sfnulc/ be at>/e to iOenti/y substances as Arrbenius adds or Arrbenius bases

3. The acidity or alkalinity of a solution can be measured by its pH value. For e v e r y c h a n g e in pH of one unit, the acidity c h a n g e s by a factor of 10 . A pH 4 solut ion is 10 t imes m o r e ac id ic that a pH 5 so lut ion. A pH 4 solut ion is 100 t imes more ac idic that a pH 6 solut ion. you shoulo tie able to laentify solutions as add base, or neutral based upon tbe pH- iVeutral is a pHorz

4. The relative level of acidity or alkalinity of a solution can be shown by using indicators.

Va r i ous ind ica tors a re s h o w n on T a b l e M. Make su re y o u know how to interpret the info on it! E x a m p l e : I F b romothymol b lue is ye l low in color , w e know the pH is 6 O R L E S S . I f its color is blue, w e k n o w the pH of the solut ion is 7.6 O R G R E A T E R .

5. In the process of neutralization, an Arrhenius acid reacts with an Arrhenius base to form a salt and water.

^ E x a m p l e : Ba (0H ) 2 + 2 HBr ^ B a B r j + 2 H j O T h e s e reac t ions a r e double r ep l a cements . T h e s e reac t ions a re NOT redox react ions . you should be able to nfite sirnple neutrali^ation reactions Urben gi\^n the reactants

6. Titration is a laboratory process in which the volume of a solution of known concentration is used to determine the concentration of another solution.

you sfmulct be able to calculate the concentration or voli/ne of a solution, using titration ctata I n o rde r to do th i s , use the t i t rat ion equa t ion o n T a b l e T : ( M x V ) ^ = ( M x V ) KM

7. The Bronsted acid - base theory views acids as "H* donors", and bases as "H* acceptors."

61

Acids & Bases - Cut from Jan 2007 - Jan 2008 Exams

1. A n Ar rhen ius base y ie lds wh i ch ion as the only negative ion in an aqueous solution'*

( 1 ) hydride iotl ( 3 ) hydronium ion ( 2 ) hydrogen ion ( 4 ) hydroxide ion

2. .According to one acid-base theory, a water molecule acts as an acid when the water molecule

( 1 ) accepts an H+ ( 3 ) donates an H+ ( 2 ) accepts an O H - ( 4 ) donates an O H -

3. Wh ich two fonnulas represent Ar rhen ius acids? ( 1 ) C H i C O O H a i i d C H j C H 2 0 H ( 2 ) H C : H 3 0 2 a n d HJPOJ ( 3 ) K H C a i a n d K H S 0 j ( 4 ) N a S C N and NinSiO:-

4. Wh i ch substance is an A n h e n i u s acid? ( 1 ) Ba (0H ) 2 ( 3 ) H 3 P O J ( 2 ) CH3COOCH3 ( 4 ) NaC I

5. Wh i ch compound releases hydroxide ions in an aqueous solution?

( 1 ) C H . i C 0 0 H ( 3 ) H C I ( 2 ) CH . iOH ( 4 ) K 0 H

10. The pl-1 o f an aqueous solution changes from 4 to 3 when the hydrogen ion concentration in the solution is (1 ) decreased by a factor o f 3/4 ( 2 ) decreased by a factor o f 10 ( 3 ) increased by a factor o f 4/3 ( 4 ) increased by a factor o f 10

1 1 . Wh i ch fonnu la represents a hydronium ion? ( 1 ) H30+ ( 3 ) 0 H -( 2 ) NH j t ( 4 ) HCO3-

12. Wh i ch compound is an Ar rhen ius acid? ( 1 ) H2S04 ( 3 ) N a O H ( 2 ) K C I ( 4 ) NH3

13. T h e table below shows the color o f the indicators methyl orange and l i tmus in two samples o f the same solution.

6. What are the products o f a reaction between K O H ( a q ) and HCI (aq ) ' '

( 1 ) H : and K C I O ( 3 ) K H and 1 IC IO ( 2 ) H2O and K C I ( 4 ) K O H and H C I

7. Wh i ch vo lume o f O . l O M NaOH(aq ) exact ly neutralizes 15.0 mi l l i l i ters o f 0.20 M H N 0 3 ( a q ) ?

( 1 ) 1 . 5mL ( 3 ) 3 . 0 m L ( 2 ) 7.5 m L ( 4 ) .30. m L

8. Wh i ch indicator, when added to a solut ion, changes color from ye l low to blue as the pH o f the solution is changed from 5.5 to 8.0?

( 1 ) broincresol green ( 3 ) l i tmus ( 2 ) bronithymol blue ( 4 ) methyl orange

9. What is the pH o f a solut ion that has a hydronium ion concentration 100 t imes greater than a solution with a p H o f 4 ?

( 1 ) 5 ( 3 ) 3 ( 2 ) 2 ( 4 ) 6

Results ot Acicl'Bftso Indicator Tests Color Result Iron) the

Indicator Test meUiyl maiLDt) yytfcjw

litmus

Wh ich pH value is consistent wi th the indicator results?

( 1 ) 1 ( 3 ) 3 (2 ) 5 ( 4 ) 1 0

14. Wh i ch ion is the on ly negative ion produced by an .Arrhenius base in water?

( 1 ) N 0 3 - ( 3 ) 0 H -(2) C I - ( 4 ) H -

62

15. Given the balanced equation representing a reaction: H2S04(aq) + 2K0H ( aq ) — K2S04(aq) + 2 H : O ( 0

VV'hicli t>'pe of reaction is represented by this equation? ( 1 ) decomposition (2 ) neutralization ( 3 ) single replacement (4 ) synthesis

16. In w h i c h 0.01 M solution is phenolphthalein p ink? ( 1 ) C H 3 0 H ( a q ) ( 2 ) Ca (0H ) 2 ( aq ) ( 3 ) C H 3 C 0 0 H ( a q ) ( 4 ) HNO? ( aq )

17. A s the pH o f a solution is changed from 3 to 6, the concentration o f hydronium ions ( 1 ) increases by a factor o f 3 ( 2 ) increases by a factor o f 1000 ( 3 ) decreases by a factor o f 3 ( 4 ) decreases by a factor o f 1000

18. W'hat co lor is bromcresol green after it is added to a sample o f NaOH(aq ) ? [ l ]

19. Ident i fy hvo indicators from Reference Tab l e A / that are y e l l ow in solutions w i th a pH o f 5.5. [ l ]

Base your answers to questions 20 and 21 on the informat ion below.

Su l fu r d iox ide , SO2. is one gas produced when fossi l fiiels are bumed. When this gas reacts wi th water in the atmosphere, an ac id is produced fonning ac id rain. T h e p H o f Uie water in a lake changes when ac id rain col lects in the lake.

T w o samples o f the same ra inwater are tested us ing two indicators. Methy l orange is ye l l ow in one sample o f this ra inwater . L i t m u s is red in ihe other sample o f this rainwater.

20, Ident i fy a possible p H value for the ra inwater that was tested. [1 ]

2 1 . Wr i te the fonnu la for one substance that can neutral ize the lake water affected by ac id rain. [1 ]

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Base your answers to questions 22 through 24 on the infonnal ion below.

A laboraior>' worker filled a bottle wi th a hydrochlor ic ac id solution. Another bottle was filled w i ih methanol, wh i le a third bottle was filled with a sodium hydroxide solution. Howeve r , the worker neglected to label each bottle. A f te r a few days, the worker could not remember which l iquid w a s in each bottle.

T h e worker needed 10 identi fy the l iquid in each bottle. T h e bottles were labeled A. 5 , and C. Us ing mater ia ls found in the lab ( indicators , conduct iv i ty apparatus, and pieces o f M g meta l ) , the worker tested samples o f l iqu id from each bottle. T h e test results are shown in the table below.

Table ol Tests and Results

Test Test Results

Test Bottle A Bottle B BottI* C

jrwthyt orange Indicatof ytfilov.' >«IIO'.V

brcxiithyiriol bkie hxlicatot blue

etectfical ciinduclh/tty conductoi i"«onGon<:lu«:3oi contluct>5(

rsactK'fr/ with Mci metal no reaction no reacticn reaction

22. Us ing the test results, slate how the worker dilTerentiated the bottle that contained methanol from the other two bottles. 111

23 . H i e worker concluded that bonle C contained hydrochlor ic ac id . Identify one test and state the corresponding test result that supports this conclusion, j 11

24. E x p l a i n , in terms o f p H , why the methyl orange indicator test results were the same for each o f the three l iquids, | l |

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Base your answers to questions 25 through 27 on llie in fonnat ion below.

In a laboratory act iv i ty . 0.500 mole o f N a O H ( s ) is complete ly d isso lved in dist i l led water to fonn 400 . mi l l i l i te rs o f NaOH(aq ) . T h i s solut ion is then used to titrate a solut ion o f HNO^(aq).

25. Identify the negative ion produced when the N a O H ( s ) is d isso lved in dist i l led water, [ l ]

26. Ca lcu late the molar i ty o f the NaOl-l(aq). Y o u r response must inc lude hoih a correct numer ica l setup and the calculated result. [2j

28. Complete the equation representing this titration reaction by wr i t ing the fonnulas o f t h e products, [ l ]

H N O ^ + N a O H -> +

Base your answers to questions 29 through 31 on the in fonnat ion below.

In preparing to titrate an ac id wi th a base, a student puts on goggles and an apron. T h e student uses burets to dispense and measure the ac id and the base in the titration. In each o f two tr ia ls , a 0.500 M N a O H ( a q ) solution is added to a f lask containing a vo lume o f H C I ( a q ) solution o f unknown concentration. Phenolphthalein is the indicator used in the titration. T l i c ca lculated vo lumes used For the two trials are recorded in the table below.

Volumes ct Base a i K l Acid Used in Titration Trials

Trial 1 Trial 2 SoJulion

•:aq} Molarity

IM] Volume U.«e<l

(mL) Volume Used

(mL) NaOH 0.500 17,03 16.87 HCI •J 10.22 10.12

29. Wr i te a chemica l name for the ac id used in the titration. [ I ]

30. Us ing the vo lumes l i o m trial I , delennine the molar i ty o f t h e l i C l { a q ) solution, [ l ]

3 1 . Based on the in fonnat ion g iven in the table, how many s igni f icant f igures should beshown in the calculated molar i ty o f t h e H C I ( a q ) solution used in trial 2? [ I ]

6 5

Topic 9: Organic Chemistry

1. Organic compounds consist of carbon atoms which bond to each other in chains, rings and networks to form a variety of structures.

^ The source of most hydrocarbons (Table Q) is petroleum, which is a mixture of many hydrocarbons.

^ The hydrocarbons in petroleum are separated from each other by distillation in a "cracking tower," on the basis of boiling points.

<̂ The greater the molar mass, the higher the intermolecular forces o f attraction between molecules. As a result, melting points and boiling points are higher, EX; Octane is a liquid at room temperature, whereas propane (the smaller molecule) is a gas, showing that it has weaker forces of attractions,

2. Organic compounds can be named with the lUPAC system. You Should know this system! Use Tables P and Q and R for help!

3. Hydrocarbons are compounds that contain only carbon and hydrogen. Saturated hydrocarbons contain only single carbon-carbon bonds. Unsaturated hydrocarbons contain at least one multiple carbon-carbon bond (double or triple bond). Hydrocarbons tend to be nonpolar molecules, and therefore do not dissolve in water. Hydrocarbons are molecular compounds that do not ionize in water, and are therefore "Non-electrolytes."

4. Organic acids, alcohols, esters, aldehydes, ketones, ethers, halides, amines, amides, and amino acids are categories of organic molecules that differ in their structures.

^ Use Table R for help! ^ Esters are the trickiest to name/draw. Review that one especially!

5. Functional groups give organic molecules distinct physical and chemical properties.

6. Isomers of organic compounds have the same molecular formula but different structures and properties.

7. In a multiple covalent bond, more than one pair of electrons are shared between two atoms. Unsaturated organic compounds contain at least one double or triple bond.

8. Types of organic reactions include: addition, substitution, polymerization, esterification, fermentation, saponification, and combustion.

You need to memorize the details of these reactions in order to be able to identify them. The Regents exam likes to go after the esterification reaction especially,

9. Empirical formulas express the simplest ration of elements in a comnpound. </' EX: Hexane - Molecular formula = Q H H & has an empirical formula of C3H7

• Propane - Molecular formula = CsHs but has no simpler formula, so CjHs is also its empirical formula

6 6

Organic Review - Cut from Jan 2007 - Jan 2008 Exams

1. W h a l is l l ie total number o f carbon atoms in a molecule o f ethanoic ac id ' '

( 1 ) 1 ( 3 ) 3 ( 2 ) 2 ( 4 ) 4

2. A double carbon-carbon bond is found in a molecule o f

( 1 ) penlane ( 3 ) pent\'ne ( 2 ) pentene (4 )pen tano l

3. G i v e n the Ibnnu las for two compounds; H H H H I : I I

H - C - C - O - C - O - H i i I I H K H H

H H H H I I I :

H -C-C-C-C~OH I I i i H H H H

These compounds d i f fer in ( 1 ) gram-fonnula mass ( 2 ) molecu lar f omiu l a ( 3 ) percent composi t ion by mass ( 4 ) phys i ca l properties at S T P

4. Wh i ch pair cons is ts o f a molecular fonnu la and its corresponding empi r i ca l fonnu la?

( 1 ) C 2 H : a n d C H i C l - l 3 ( 3 ) PuOioand P2O5

(2) CeHf, and C 2 H : ( 4 ) S O : and SO3

5. T h e organic compound represented by the condensed structural f onnu l a C H i C f h C h h C H O is c lass i f i ed as an

( 1 ) a lcohol ( 3 ) ester ( 2 ) aldehyde ( 4 ) ether

6. W h i c h two fonnu las represent An 'hen ius ac ids? ( 1 ) CH3COOH and CH3CH2OH

(2) H C : H j 0 2 a n d H 3 P O j ( 3 ) K H C O . i and K H S O J ( 4 ) N a S C N and N a i S a O )

7. W h i c h compound is an unsaturated hydrocarbon? ( l ) h e x a n a l ( 3 ) hexano ic ac id ( 3 ) hexane ( 4 ) hexene

8. Wh i ch fonnula represents an alkene? ( 1 ) C2Hf, ( 3 ) C J H I O ( 2 ) C3Hf, ( 4 ) C 5 H i 2

9. What is the total number of pairs of electrons shared between the carbon atom and the oxygen atom in a molecule of inethanal?

( 1 ) 1 ( 3 ) 3 ( 2 ) 2 ( 4 ) 4

10. Wh i ch compound is a saturated hydrocarbon? ( 1 ) CH2CH2 (3)CH3CHO ( 2 ) CH.3CH3 (4)CH.iCH20H

11. A molecule of a compound contains a total of 10 hydrogen atoms and has the general fonnula C';H2M+2.

Wl i i ch prefix is used in the name of this compound? ( 1 ) but- (3)oct-( 2 ) dec- (4 )pen t-

12. A molecule of butane and a molecule of 2-butene both ha\ the same total number of

( 1 ) carbon atoms ( 3 ) single bonds ( 2 ) hydrogen atoms ( 4 ) double bonds

13. Wh i ch general fonnula represents the homologous series of hydrocarbons that includes the compound 1-heptyne?

( 1 ) C,.H2,,̂ . (3)C»H2,.

( 2 ) C,>H2„-2 (4)C«H2»*2

14. Wh i ch two compounds are isomers of each other? ( 1 ) CH3CH2COOH and CH3COOCH2CH3

( 2 ) CH3CH2CHO and CH3COCH3

( 3 ) CH3CHBrCH3andCH2BrCHBrCH3 ( 4 ) CH3CHOHCH3 and CH3CHOHCH2OH

67

15. Wh ich fonnula represents an unsanirated hydrocarbon?

H - C - C - H I i H H

H H

H H

H H

H - C - C - H I I H CI

( 3 )

H H

19. Wh i ch structural f onnu l a represents an unsaturated hydrocarbon' '

H H

H - C - C - H I I H H

( 1 )

O

c \

OH

H H

H" ' H

( 3 )

C=-0

( 2 i { 4 )

16. A compound has a molar mass o f 90 . grams per mole and Ihe empir ica l fonnula CI-I2O. WTial is die molecular fonnu la o f this compound?

( 1 ) CH20 ( 3 ) C 3 H 6 0 3 ( 2 ) C2HJ02 ( 4 ) C 4 H 8 0 4

17. G i v e n the formula o f a substance;

H H H H \ I y

C.»C-C=-C / \

H H

Whal is the total number o f shared electrons in a molecule o f this substance?

( 1 ) 22 ( 3 ) 9 ( 2 ) 11 ( 4 ) 6

18. G i v e n the structural fonnula :

H H H H O I 1 I I II

H - C - C - C - C - C - O H I i I I H H H H

What is the l U P A C name o f this compound? ( 1 ) pentanal ( 3 ) meihyl penianoate ( 2 ) pentanol ( 4 ) pentanoic ac id

20. T w o substances ha\ different physical and chemica l properties. Bo th substances have molecules that contain two carbon atoms, one oxygen atom, and s i x hydrogen atoms. These hvo substances must be ( 1 ) isomers o f each other ( 2 ) isotopes o f each other ( 3 ) the same compound ( 4 ) the same hydrocarbon

2 1 . G i v e n the balanced equation rcpresenliiig a reaction: CH3CH2CH1 + Br. — CH3CH2CH2Br + H B r T h i s organic reaction is best classified as ( 1 ) an addition reaction ( 2 ) an esterification reaction ( 3 ) a polymerization reaction ( 4 ) a substitution reaction

22. G i v e n the structural fonnula:

H - C ! i s C - H What is the total number o f electrons shared in the bond between the two carbon atoms?

(1) 6 ( 3 ) 3 (2) 2 ( 4 ) 4

68

Base your answers lo questions 23 and 24 on the information below.

Ozone gas. 0^, can be used to k i l l adult insects in storage bins for grain without damaging the grain. T h e ozone is produced from oxygen gas. O2, in portable ozone generators located near the storage bins. T h e concentrations o f ozone used are so low that they do not cause any env i ronmenta l damage. T h i s use o f ozone is safer and more env i ronmenia l l y friendly than a method that used bromomethane, C H . i B r Howeve r , bronioinethane was more e l e c t i v e than ozone because C H i B r k i l l ed immature insects as we l l as adult insects.

Adapted From: Ptc Sumlay-Cazetw (Schenectady, NY) 3/9/03

23. Determine the total number o f moles o f C H ? B r in 19 grams o f C H . i B r (gram-fonnula mass ^ 95 gram&'mol). [ I j

24, G i v e n the balanced equation for producing bromomethane: B r : + C H 4 - C H 3 B r + H B r

Identify the t\̂ pe o f organic reaction shown. [1 ]

25 . Wr i te the empir ica l fonnu la for the compound C s H i s .

Base your answers to questions 26 through 28 on the infonnat ion below.

T h e incomplete equation be low represents an esterif icat ion reaction.

T h e alcohol reactant is represented by X. H O H O H H H

H - C - C - O H * X - ^ — ^ H " C " - C ~ 0 - C " C - C - H + H^O 1 ; ; 1 I H H H H H

26. On the reaction above, c i rc le the acid functional group. [ i ]

27. Wr i te an l U P A C name for the reactant represented by its structural fonnu la i n this equation, [ l ]

28. D r a w the st i i i c lura l fonnu la for the alcohol represented by X.

69

29. E.xplain, in terms o f molecular structure or distribution o f charue. why a molecule o f methane is nonpolar. [1]

Base your answers to questions 30 and 31 on the infonnat ion below.

T h e graph below shows the relat ionship between boi l ing point and molar mass at standard pressure for penlane, he,\ane. heptane, and nonane.

Boiling Point Versus Molar Mass of S o m e A l k x i n e s

160.

U O .

0 120.

1 10G. CL at S 8 0 , •5 CO

6 0 ,

40, 20,

i ! j j

1

n 1

1 1 (j

» , ICO, 110.

Molar Maaa fr/mol)

130,

30. Octane has a molar mass o f 114 grams per mole. Accord ing lo this g-raph, what is Ihe boi l ing point o f ociane at standard pressure? [ 11

3 1 . Stale the relat ionship between molar mass and the strength o f i i i len i io lecular forces for the selected alkanes. 111

7 0

Topic 10: Ph^se? » Gases

1. The three phases of matter are solid, liquid and gas. Each has its own properties. Sol ids h a v e a cons tan t vo l ume and shape . Par t i c les a r e held in a r igid, c rysta l l ine s t ruc tu re . L iqu ids have a cons tan t vo lume but a chang ing s h a p e . Par t ic les a re mobi le but sti l l he ld together by s t rong a t t rac t ion . G a s e s h a v e no se t vo l ume or shape . T h e y wil l comple te l y fill any c losed con ta ined . Par t i c les have largely b roken f ree o f the fo r ces holding t h e m together .

2. A heating curve (or cooling curve) traces the changes in temperature of a substance as it changes from solid to liquid to gas (or gas to liquid to solid).

W h e n the subs t ance undergoes a phase c h a n g e , the re is no change in t empe ra tu re . T h e line " f l a t t e n s " unt i l the phase change is comple te . W h e n a phase change is occur r ing , the potent ia l ene rgy of the subs t ance c h a n g e s wh i le kinetic ene rgy r e m a i n s the s a m e . As t e m p e r a t u r e i nc reases , k inet ic ene rgy i n c r ea se s .

3. Heat of fusion (Hf) is the energy needed to convert one gram of a substance from solid to liquid.

4. Heat of vaporization (H,) is the energy needed to convert one gram of a substance from liquid to gas.

5. Specific heat (C) is the energy required to raise one gram of a substance 1 degree (Celcius or Kelvin). ^ T h e spec i f i c hea t o f l iquid w a t e r is 1 ca l/g* J or 4 .2 J / g * K .

6. The combined gas law states the relationship between pressure, temperature and volume in a sample of gas.

I n c r e a s i n g p re s su re c a u s e s a d e c r e a s e in v o l u m e ( i n ve r s e re la t ionsh ip ) . I n c r e a s i n g t empera tu re c a u s e s an inc rease in vo l ume (d i rect re la t ionsh ip ) . I n c r e a s i n g t empe ra tu r e c a u s e s an inc rease in p ressu re . (d i r ec t re la t ionsh ip ) . ( P V / T ) i = (PV/T)2 r eminder ! ! All t e m p e r a t u r e s m u s t be in the Ke lv in sca le w h e n us ing th is equat ion

7. An ideal gas model is used to explain the behavior of gases. An "ideal gas" would perfectly obey the combined gas law (PV/T) at all conditions of temperature and pressure.

A rea l g a s is mos t like an ideal g a s w h e n it is a t h igh t empera tu re and low p ressu re . I n other w o r d s , a t condi t ions w h i c h wou ld favor the g a s s tay ing in the g a s phase ( a n d not l iquefy ing) . T h e rea l g a s e s tha t m o s t r e semb le Ideal g a s e s a re H j and He .

8. The Kinetic Molecular Theory (KMT) for an ideal gas states that all gas particles: a r e in r a n d o m mot ion . h a v e no forces of a t t r a r t i on b e t w e e n t hem. h a v e a negl ig ib le vo l ume c o m p a r e d to the d i s t ances be tween t h e m . h a v e co l l i s ions tha t resu l t in the t r ans fe r o f ene rgy f rom one part ic le to ano the r , w i th no net loss of ene rgy f r o m Che col l is ion.

9. Equal volumes of gases at the same temp and pressure have an equal number of particles.

71

Phases & Gases - Cut from Jan 2007 - Jan 2008 Exams

1. T h e boi l ing point o f a l iquid is the temperature at wh ich the vapor pressure o f t h e l iqu id is equal 10 the pressure on the surface o f t h e hquid. What is the boil ing point o f propanone i f the pressure on its surface is 48 k i lopasca ls?

( 1 ) 25°C ( 3 ) 3 5 ° C ( 2 ) 30.°C (4 )40 . °C

2. A t w h i c h Ce l s ius temperature does lead change from a sol id to a l iquid?

( 1 ) 874»C ( 3 ) 328°C ( 2 ) 601°C ( 4 ) 0 ' ' C

3. T h e table below shows data for the temperature. pressure, and volume o f four gas samples.

Data tor Four Gas Samples

Gas Sample

Temperature (K)

Pressure (atm)

Volume .;mL)

A 1M. 2 •too.

B 200. 2 2M .

C. too. 2 400.

D 200. 4 2W.

Which two gas samples have die same total number o f molecules?

( 1 ) /4and/ i ( 3 ) / ^ a n d C ( 2 ) /I and C ( 4 ) / J a n d O

4. A i wh i ch temperature is the vapor pressure o f ethanol equal to the vapor pressure o f propaiione at 35°C?

( I ) 3 5 ° C ( 3 ) 8 2 ° C q(2)60. °C ( 4 ) 9 5 ° C

5. A rigid cy l inder w i th a movable piston contains a 2.0-liter sample o f neon gas at S T P . What is the vo lume o f this sample when its temperature is increased to 30.°C wh i l e its pressure is decreased to 90. k i lopasca ls ?

( 1 ) 2 . 5 L ( 3 ) 1 . 6 L ( 2 ) 2 , 0 L ( 4 ) 0,22 L

6. Wh i ch ke lv in temperature is equal to 5 6 X ? ( 1 ) - 3 2 9 K ( 3 ) 2 1 7 K ( 2 ) - 2 1 7 K ( 4 ) 3 2 9 K

7. A sample o f gas i s held at constant pressure. Increasing the ke lv in temperature o f this gas sample causes the average kinetic energy o f its molecules to ( 1 ) decrease and the vo lume o f the gas sample to decrease ( 2 ) decrease and the vo lume o f the gas sample lo increase ( 3 ) increase and die vo lume o f the gas sample to decrease ( 4 ) increase and the vo lume o f the gas sample to increase

8. At S T P , wh ich sample contains the same number o f molecules as 11,2 liters o f C 0 2 ( g ) at S T P ? ( l ) 5 . 6 L o f N 0 2 ( g ) ( 3 ) 1 1 . 2 L o f N 2 ( g ) { 2 )7 . 5Lo fH2 ( g ) ( 4 ) 2 2 . 4 L o f C O ( g )

9. A t wh i ch temperature wou ld atoms o f a l l e ( g ) sample have the greatest average k inet ic energy?

( 1 ) 2 5 X ( 3 ) 273 K (2 ) 3 7 X ( 4 ) 298

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10. A I OO-mole sample o f neon gas occupies a vo lume o f 24.4 l i ters at 298 K and 101.3 k i lopasca ls . In the space in your answer booklei, calculate the density o f this sample. Y o u r response must include holb a correct numerica l setup and the ca lculated result. [2 ]

Base your answers to quest ions 11 through 14 on the infonnat ion below.

T h e temperature o f a sample o f a substance is increased from 20.°C to 160.°C as the sample absorbs heat at a constant rale o f 15 k i lo jou les per minute at standard pressure. T h e graph below represents the relat ionship between lemperat iue and time as the sample is heated.

180,

Tomporature Versus Time

4.0 e.o 8.0 T ime (min)

12.0

11. What is the boi l ing point o f this sample? [ i j

12. D raw al has/ nine part icles in the box, showing the correct pa i l i c le arrangement o f this sample during the first minute o f heating, [ l ]

13. What IS the total t ime this sample i s in the l iqu id phase, on ly? { l ]

14, Detenn lne the total amount o f heat required to complete ly melt this sample at its melt ing point, [ l ]

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Base your answers to questions 15 through 17 on the infonnat ion below,

A r igid cy l inder is Fitted wi th a movable piston. T l i e cy l inder contains a sample o f hel ium gas, He (g ) , wh i ch has an init ia l volume o f 125.0 mi l l i l i t e rs and an init ial pressure o f 1.0 atmosphere, as shown below. T h e temperature o f the hel ium gas sample is 2 0 . 0 X .

'-y. Handle

Pressure gauge

15. Express the Initial volume o f the he l ium gas sample, in liters, [ l ] L i t e r s

16. The piston is pushed ftirther Into the cy l inder. Show the correct numerical setup for calculat ing the vo lume o f the he l ium gas that is anticipated when the reading on the pressure gauge is 1.5 atmospheres. T l i e temperature o f the hel ium gas remains constant, [ l ]

17. He l ium gas is removed from the cy l inder and a sample o f nitrogen gas, N2(g), is added to Ihe cy l inder. T h e nitrogen gas has a volume o f 125.0 mi l l i l i ters and a pressure o f 1.0 atmosphere at 2 0 , 0 X . Compare the number o f pan ic les in this nitrogen gas sample to the number o f particles in the original hel ium gas sample, [ l ]

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Topic 11: Electrochemistry (Oxidation-Reduction Reactions! Outline

1. In all chemical reactions there is a conservation of mass, energy, and charge.

2. An oxidation-reduction (redox] reaction involves the transfer of electrons (e-).

3. Reduction is the gain of electrons.

A half-reaction can be written to represent redurtion.

For example: CI2 + 2 e" 2 CI'"

4. Oxidation is the loss of electrons.

A half-reaction can be written to represent oxidation.

For example: Na Na* -1- 1 e

5. Oxidation numbers (states) can be assigned to atoms and ions. Changes in oxidation numbers indicate that oxidation and reduction have occurred.

Be able to use an artivit/ series (Reference Table J) to determine whether a redox reaction is spontaneous.

6. In a redox reaction the number of electrons lost is equal to the number of electrons gained.

•f This supports the fact that charge is always conserved!

7. An electrochemical cell can be either voltaic or electrolytic. In an electrochemical cell, oxidation occurs at the anode and reduction at the cathode.

Be able to compare and contrast voltaic and electrolytic cells.

8. A voltaic cell spontaneously converts chemical energy to electrical energy.

Identify and label the parts of a voltaic cell (cathode, anode, salt bridge) and direction of elertron flow, given the reaction equation.

Since this reaction is spontaneous, use Ref. Table J to help you determine what is the anode (oxidation) and the cathode (reduction). The most reactive metal will oxidize, the most reactive non-metal will reduce.

9. An electrolytic cell requires electrical energy to produce a chemical change. This process is known as electrolysis.

^ Identify and label the parts of an electrolytic cell (cathode, anode) and direction of electron flow, given the reaction equation

Since this reaction is non-spontaneous, use Ref. Table J to help you determine what is the anode (oxidation) and the cathode (reduction). The most reactive metal will reduce, the most reactive non-metal will oxidize. (NOTE: This is the opposite of what metals/non-metals want to do!)

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Electrochemistry Practice Questions

1. G i v e n ihe equat ion:

_ C a ^* (fl(/) + _ P O j ' ' («(/) ^ _ C a . , ( P O j ) : ( , v )

W h e n Ihe equat ion is cor rec t l y ba lanced , the s u m o f the total charge o f the reactants is

( 1 ) 0 ( 3 ) - 3 ( 2 ) +2 ( 4 ) + 6

2. T h e net ion ic equat ion: F e ( i ) + Pb-*(ai/) -> Fe-*(or/) + Pb(.v)

i l lustrates conserva t ion o f

( 1 ) mass and charge ( 2 ) charge but not mass ( 3 ) mass but not charge ( 4 ) neither mass nor charge

3. A s an atom o f ni trogen ga ins e lect rons , its ox ida t ion number

7. In w h i c h substance is the ox ida t ion number o f C I equal to + l ' '

( 1 ) C h ( 3 ) A I C l 3 ( 2 ) C l 2 0 ( 4 ) H C I 0 2

8. Wha t is the ox ida t i on number o f c h r o m i u m in K z C r j O r ?

( 0 + 12 ( 3 ) + 3 ( 2 ) + 2 ( 4 ) + 6

9. O x y g e n has an ox ida t i on number o f - 2 in

( 1 ) 0 , ( 3 ) N a , 0 2 ( 2 ) N 0 2 ( 4 ) O F :

10. In w h i c h compound does ch lo r ine have ihe highest ox ida t i on number?

( 1 ) N a C ! 0 ( 3 ) N a C I O j ( 2 ) N a C I 0 2 ( 4 ) N a C I 0 4

( 1 ) decreases ( 2 ) increases 11 . In w h i c h compound does carbon have an ( 3 ) rema ins the same ox ida t ion stale o f - 4 ?

4. W h e n a neutral atom undergoes ox ida t i on , the a t o m ' s ox ida t i on state

( 1 ) decreases as it gains e lec t rons ( 2 ) decreases as it loses e lec t rons ( 3 ) increases as i l gains e lec t rons ( 4 ) increases as it loses e lec t rons

5, I n w h i c h substance does hydrogen have an ox ida t ion number o f zero?

( 1 ) LiH ( 2 ) H , 0

( 3 ) H2S ( 4 ) H ,

6. W h a l is the ox ida t ion number o f ch lo r ine i n H C I O j ?

( 1 ) + I ( 2 ) +5

( 3 ) + 3 ( 4 ) +7

( 1 ) C O ( 2 ) C 0 2

( 3 ) C C l 4 ( 4 ) C H j

12. Wha t is Ihe ox ida t i on number o f ca rbon in N a H C O , ' '

( 1 ) +6 ( 2 ) +2

( 3 ) -4 ( 4 ) +4

13. G i v e n the react ion :

Cu(.v) + 4 H N 0 , ( m / ) - > Cu(NO,,)2(rt</) + 2NO,(.s; ) + 2W^O(l)

A s the react ion occurs , what happens lo copper ?

( 1 ) It undergoes reduct ion and its ox ida t ion number decreases

( 2 ) It undergoes reduct ion and its ox ida t ion number increases .

( 3 ) It undergoes ox ida t ion and its ox ida t i on number decreases

( 4 ) It undergoes ox ida t ion and its o x i d a l i o n number increases.

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14. W h i c h component o f a vo l ta i c ce l l is co r rec t l y paired w i th its func t ion?

{ I ) ex te rna l conductor — a l l o w s the so lu t ions to m i x

( 2 ) ex te rna l conductor — permi ts the migra t ion o f ions

( 3 ) salt br idge — a l l o w s the so lu t ions to m i x ( 4 ) salt br idge — pemi i t s the migra t ion o f

ions

15. T h e d i ag ram represents a c h e m i c a l ce l l at 2 9 8 K.

Switch

2Ai ( s ) .3Nr (ao)- - 2 * 1 ' »3Ni(s)

W h e n the s w i t c h is c l o sed , e lec t rons flow f rom ( 1 ) A l ( .v ) to Ni( ,v) ( 2 ) Ni(.v) to Al ( ,v ) ( 3 ) A l ' * ( m y ) to Ni-*(ar/) ( 4 ) H\-\aii) to Al ' * ( (K/)

16. W h i c h redox equat ion is co r rec t l y ba lanced? ( I j C r ' ^ + M g ^ C r + M g - * ( 2 ) A 1 - * + K ^ A l + K * ( 3 ) S n " * + H , ^ S n + 2 H * ( 4 ) B r j + H g ^ Hg^* + 2 B r "

17. W h i c h statement best desc r ibes h o w a salt br idge ma in t a i n s e l ec t r i ca l neutra l i ty in the ha l f-ce l l s o f a vo l t a i c c e l l ?

18. G i v e n the reac t ion ;

_ H g - * + _ A g " ^ _ H g " + _ _ A g ' *

W h e n the equat ion is comp le t e l y ba lanced us ing the sma l l e s t who le-number c o e n k i e n t s , the c o e f f i c i e n l o f H g w i l l be

( 1 ) 1 ( 2 ) 2

( 3 ) 3 ( 4 ) 4

19. T h e d i ag ram s h o w s a vo l t a i c ce l l . T h e react ion oc cu r s at 1 a lmosphere and 2 9 8 K .

Switch

Zn(s) + Pb' (aq) • Zif(aq» * Ph*(s)

W h e n Ihe s w i t c h is c l o sed , what o c cu r s ?

( 1 ) Pb is o x i d i z e d and e lec t rons l l o w to the Z n e lec t rode .

( 2 ) Pb is reduced and e lec t rons f l o w to the Z n e lect rode.

( 3 ) Z n is o x i d i z e d and e lec t ions l l o w lo the Pb e lectrode.

( 4 ) Z n i s reduced and e lec t rons f l o w to Ihe Pb e lec t rode

2 0 W h i c h meta l c a n replace C r in C r ^ O j ?

( 1 ) n i cke l ( 3 ) c o p p e r ( 2 ) lead ( 4 ) a l u m i n u m

( 1 ) It prevents the m ig ra t ion o f e lectrons. ( 2 ) I I p em i i t s the m ig ra t i on o f ions . ( 3 ) I I p em i i t s the t w o so lu t i ons l o m i x

comple te l y . ( 4 ) It prevents the reac t ion f r o m o c c u r i n g

spontaneous ly .

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2 1 . G i v e n the react ion :

2Cr( .v) + _ S n - * ( a ( / ) 2Cr'*(t«/) + _ S n ( . v )

W h e n the react ion is correct ly ba lanced us ing the smal les t w h o l e numbers , the coef f t c ien l o f Sn"*(a</) is

( 1 ) 1 ( 3 ) 3 ( 2 ) 2 ( 4 ) 4

22 . A n e l ec t rochemica l ce l l that generates e lec t r i c i t y conta ins hal f-cel ls thai produce

( 1 ) o x i d a l i o n hal f-react ions, on l y ( 2 ) reduct ion hal f-react ions, on l y ( 3 ) spontaneous redox react ions

( 4 ) nons ix in i aneous redox react ions

2 3 . G i v e n Ihe react ion :

2L i ( . v ) + C l : ( j ; ) 2 L i C l ( . v )

A s Ihe react ion takes place, the C\i(ii) w i l l

( 1 ) ga in e lectrons ( 3 ) ga in protons ( 2 ) lose e lectrons ( 4 ) lose protons

24 . In Ihe react ion C u + 2 A g * C u ' * + 2 A g , the o x i d i z i n g agenl is

(1 ) C u ( 3 ) A g * ( 2 ) C u " ( 4 ) A g

2 5 . W h i c h procedure requires the use o f an externa l e lec t r i c current to force a redox react ion to occu r ?

( 1 ) po l ymer i za t i on ( 2 ) d i s t i l l a t ion ( 3 ) e l ec t ro l ys i s ( 4 ) sapon i f i ca t ion

26. A n e lec t ro ly t i c c e l l is d i f ferent f rom a vo l t a i c ce l l because in an e lec t ro ly t i c ce l l

( 1 ) a redox react ion occurs ( 2 ) a spontaneous react ion occurs ( 3 ) an e lectr ic current is produced ( 4 ) an e lectr ic current causes a che in i ca l

react ion

27. T h e d iagram shove's an e lect ro ly t ic ce l l in w h i c h the e lectrodes are t in and copper.

SWITCH

S O L U T I O N

W h e n the s w i t c h is c losed, what w i l l happen lo Ihe two e lect rodes?

(\) B w i l l d i s so l v e and A w i l l become coated w i th t in.

( 2 ) A w i l l d i s so l ve and ti w i l l become coated w i th t in.

( 3 ) H w i l l d i s so l v e and/ I w i l l become coated w i t h copper.

( 4 ) A w i l l d i s so l v e and B w i l l become coated w i th cop|)er.

28 . W h i c h s l a l emen i best descr ibes the react ion represented by Ihe equat ion be l ow?

2NaCI + 2H2O + e l ec t r i c i t y -> C I ; + H , + 2 N a O H

( 1 ) T h e react ion occurs in a vo l ta i c ce l l and re leases energy .

(2) T h e react ion occu rs in a vo l t a i c ce l l and absorbs energy .

( 3 ) T h e react ion occu rs in an e lec t ro l y t i c ce l l and re leases energy.

( 4 ) T h e react ion occu rs in an e lec t ro ly t i c ce l l and absorbs energy.

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29 . What is the ox ida t i on state o f ni trogen in the compound NH . |B r ?

( 1 ) - I ( 2 ) +2

( 3 ) -3 ( 4 ) +4

30 . G i v e n the unba lanced ion ic equat ion:

3 M g + F e ' * 3Mg-* + Fe

W h e n this equat ion is ba lanced , both F e ' * and Fe have a c o e n i c i e n t o f

( 1 ) 1, because a total o f 6 e lectrons is t ransferred

( 2 ) 2, because a total o f 6 e lectrons is t ransfer red

( 3 ) 1, because a total o f 3 e lectrons is t ransferred

( 4 ) 2, because a total o f 3 e lec t rons is t ransfer red

3 1 . A studeni co l l ec t s the mater ia l s and equipment be low to cons l rac t a vo l t a i c ce l l .

• two 2 5 0 - m L beakers • w i r e and a s w i t c h • one s t r ip o f m a g n e s i u m • one s t r ip o f copper • 125 m L o f 0 .20 M M g ( N O j ) ! ( a q ) • 125 m L o f 0 .20 M C u ( N O , ) : ( a q )

W h i c h add i t iona l i tem is required for the cons tn i c t i on o f t h e vo l t a i c c e l l ?

( 1 ) an anode ( 2 ) a batter>'

( 3 ) a cathode ( 4 ) a salt br idge

3 2 . T h e d iag ram be low represents an opera t ing e l ec t rochemica l ce l l and the ba lanced ion ic equat ion for the react ion occu r r i ng in the c e l l .

Wire Wire

Voltmeter

Zn{s) / '' Salt bndoe

Zn^*(aq)

Zn(s) + N i ' ' ( aq ) — Zn^'(aq) + Ni is j

W h i c h statement ident i f ies the pan o f t h e ce l l that conducts e lec t rons and descr ibes the d i rec t ion o f e lec t ron l l o w as the ce l l operates?

( 1 ) E l ec t rons f l o w through the salt br idge f rom the N i ( s ) to the Z n ( s ) .

( 2 ) E l e c t rons f l o w through the salt br idge f rom the Z n ( s ) to the N i ( s ) .

( 3 ) E l e c t rons f l o w through the w i r e f r om the N i ( s ) to the Z n ( s ) .

( 4 ) E l e c t rons f l o w through the w i r e f rom the Z n ( s ) to the N i ( s ) .

Base y o u r a n s w e r s to quest ions 33 through 35 on the in format ion below.

In a l abora tory inves t iga t ion , magnes ium r e a d s w i t h hyd roch lo r i c ac id to produce hyd rogen gas and m a g n e s i u m ch lo r ide . T h i s react ion i s represented by the unbalanced equat ion be low.

M g ( s ) + H C I ( a q ) -> H2(g) + M g C l : ( a q )

3 3 . State , in t e rms o f t h e re la t i ve ac t i v i t y o f e l ements , w h y this react ion is spontaneous. [ I ]

34 . B a l a n c e the equat ion above, us ing the smal les t who le-number coe f f i c i en ts . [1]

3 5 . W r i t e a ba l anced ha l f-react ion equat ion for the ox ida t i on that occurs . [ I ]

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Base y o u r answers to quest ions 36 through 37 on the informat ion below.

T h e d iagram be low s h o w s a s ys t em in w h i c h water is being decomposed into oxygen gas and hydrogen gas L i t m u s is used as an ind icator in the water. T h e l i tmus turns red in test tube I and blue in test tube 2.

? 1 Battery O, g a s

Vi/ater containing an electroly:e a n d litmus

H, gas

Electrodes

Test tube Test tube 1 2

T h e ox ida t ion and reduct ion occun-ing in Ihe test tubes are represented by the balanced equat ions be low.

T e s t tu\w 1: 2 IM ) l f I OMg) + 4f r ( aq> + ^ e "

Te . r t t i i h e 2 ; 11 U O i . e i + l e ' -~> 2H,i^} + - l O i r i a q )

36 . Ident i fy Ihe in fo rmat ion in the d i ag ram that indicates this sys tem is an e l e c t ro l y t i c ce l l . [ I ]

37 De te rmine the change in o x i d a l i o n number o f o x y g e n dur ing the react ion in lest lube 1. [I]

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Base y o u r a n s w e r s lo questions 38 through 4U on the d i ag r am below.

T h e d i ag ram s h o w s a vo l ta i c ce l l w i th copper and a l u m i n u m e lectrodes immed i a t e l y a f ter the e.vtemal c i rcu i t i s comple ted .

Voltaic Cell

Wire

Cu(s) electrode —Al(s) electrode

Half-celt 1 Half-cetl 2

38. B a l a n c e the redox equat ion be low us ing Ihe sma l l e s t who le-number coe f f i c i en t s [ 1 ]

C j i - n a ( | ) + A l l ? ) _ C n i s ) + A P ' l a q )

39 . A s th is vo l t a i c ce l l operates, the m a s s o f the A l ( s ) e lectrode decreases . E x p l a i n , in t e n n s o f par t i c les , w h y th is decrease in mass occurs . [ 1 ]

4 0 . E x p l a i n Ihe func l i on o f the sa i l br idge. [ I ]

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Base y o u r answers to questions 41 through 44 on the informat ion below.

In a laboratory inves t iga t ion , a student constructs a vo l t a i c ce l l w i th iron and copper electrodes. A n o t h e r student cons l ruc i s a vo l t a i c ce l l w i th z inc .and iron electrodes. T e s t i n g the ce l l s dur ing operat ion enables the students lo wr i te the ba lanced ion ic equat ions be low.

C e l l w i t h iron and copper e lectrodes: C u " * ( a q ) + F e ( s ) C u ( s ) + F e ' * ( a q ) C e l l w i t h z i n c and iron electrodes: Fe".*(aq) + Z n ( s ) F e ( s ) + Zn-.*(aq)

4 1 . S ta le ev idence f r o m the ba lanced equat ion for Ihe ce l l w i i h i ron and copper electrodes thai indicates the react ion in Ihe ce l l is an ox idat ion-reduct ion react ion. [ 1 ]

42 . Ident i f y Ihe par t i c les t ransferred between F e " * and Z n dur ing the react ion in Ihe ce l l w i th z i n c and iron electrodes. [1 ]

4 3 . W r i t e a ba lanced hal f-react ion equat ion for the reduct ion that l akes place in Ihe ce l l w i th z i n c and iron e lectrodes, [ I ]

44 . S late the re lat ive ac t i v i t y o f t h e three meta ls used in these two vo l ta i c c e l l s . [ I ]

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