Stoichiometry• Greek Translation

– Stoicheion – means “element”

– Metron – means “measure”

• Element Measuring

StoichiometryEQ: How do we compare elements so that

we can measure them?

For example, does…

23 grams of Na = 23 grams of Cl

23g Na x 1 mol = 1 mol Na or 6.022E23 atoms

23g

23g Cl x 1mol = 0.65 mol Cl or 3.85E23 atoms

35.5g

StoichiometrySo how much Chlorine do I need since

NaCl is a one to one ratio?

23g Na x 1 mol = 1 mol Na or 6.022E23 atoms

23g

35.5g Cl x 1mol = 1 mol Cl or 6.022E23 atoms

35.5g

23g Na = 35.5g Cl

StoichiometryWhat if all I had was 23 grams of Chlorine?

How much NaCl could l make?

23g Na x 1 mol = 1 mol Na or 6.022E23 atoms

23g

23g Cl x 1mol = 0.65 mol Cl or 3.85E23 atoms

35.5g

Limiting Reagent

Chemical Stoichiometry

Stoichiometry - The study of quantities of materials consumed and produced in chemical reactions.

Mole MoleMass MoleMole MassMass Mass

Consumed Produced

Review: The Mole

The number equal to the number of carbon atoms in exactly 12 grams of pure 12C.

1 mole of anything = 6.022 ´ 1023 units of that thing

Review: Molar Mass

A substance’s molar mass (molecular weight) is the mass in grams of one mole of the compound.

CO2 = 44.01 grams per mole

H2O = 18.02 grams per mole

Ca(OH)2 = 74.10 grams per mole

Review: Chemical EquationsChemical change involves a reorganization of

the atoms in one or more substances.

C2H5OH + 3O2 2CO2 + 3H2O

reactants products

1 mole of ethanol reacts with 3 moles of oxygen to produce 2 moles of carbon dioxide and 3 moles of water

When the equation is balanced it has quantitative significance:

Mole to Mole ProblemsAmmonia, NH3, is widely used as fertilizer and in many

household cleaners. How many moles of ammonia are produced when 6 mol of hydrogen gas react

with an excess of nitrogen gas?

N2 + H2 NH3 2=N=1 2=H=3 23

6 mol H2(g)

mol unknownmol known

X 2 mol NH3 = 4 mol NH3

3 mol H2

Step 1: Step 2:Step 3:

Step 4:

Mole to Mole ProblemsThe decomposition of potassium

chlorate, KClO3, is used as a source of oxygen in the laboratory. How many

moles of potassium chlorate are needed to produce 15 mol of oxygen?

Mole to Mass ProblemsIn photosynthesis, plants use energy from the sun

to produce glucose, C6H12O6, and oxygen from the reaction of carbon dioxide and water. What mass, in grams, of glucose is produced when 3.00 mol of water react with carbon dioxide?

6CO2 + 6H2O C6H12O6 + 6O2

3.00 mol H2O X 1 mol C6H12O6 X

6 mol H2O 180.18g = 1 mol

C6 X 12.01 = 72.06H12 X 1.01 = 12.12O6 X 16.00 = 96.00 180.18g/mol

90.09g C6H12O6

Mole-Mass ProblemSolution of iron (III) chloride, FeCl3, are used in

photoengraving and to make ink. This compound can be made by the following reaction.

2 Fe + 3 Cl2 ---------> 2 FeCl3

How many grams of FeCl3 form from 2.4 moles of Fe?

Mass to Mole ProblemsThe first step in the industrial manufacture of nitric acid is the

catalytic oxidation of ammonia.

NH3 + O2 NO + H2O (unbalanced)

The reaction is run using 824 g of NH3 and excess oxygen.

a. How many moles of NO are formed?

b. How many moles of H2O are formed?

4 5 4 6

A. 824g NH3 X 1 mol X 4 mol NO = 48.39 mol NO 17.03g NH3 4 mol NH3

N X 14.00 = 14.00H3 X 1.01 = 3.03 17.03g/mol

B. 824g NH3 X 1 mol X 6 mol H2O = 72.58 mol H2O 17.03g NH3 4 mol NH3

Mass to Mole ProblemsOxygen was discovered by Joseph Priestley in

1774 when he heated mercury (II) oxide to decompose it to form its constituent elements.

a. How many moles of mercury (II) oxide are needed to produce 125 g of oxygen?

b. How many moles of mercury are produced?

Mass to Mass ProblemsWhen copper metal is added to silver nitrate in solution, silver

metal and copper (II) nitrate are produced. What mass of silver is produced from 100. g of Cu?

Cu + Ag(NO3) Ag + Cu(NO3) +2 -1

22 2

100g Cu X 1 mol Cu X 2 mol Ag X 107.87g = 339.48g Ag 63.55g 1 mol Cu 1 mol Ag

Molar Mass Molar Mass

Mass to Mass ProblemsTin (II) fluoride is used in some toothpastes. It is

made by the reaction of tin (II) with hydrogen fluoride according to the following equation.

Sn + 2 HF SnF2 + H2

How many grams of SnF2 are produced from the reaction of 30.00 g of HF with Sn?

Mole-MoleHow many moles of carbon dioxide, CO2, can be made from Fe2O3 by the use of 1.90 moles of carbon monoxide, CO, in the following reaction? Fe2O3 + 3 CO -----------> 2 Fe + 3 CO2

Mole- Mass ProblemMole- Mass Problem

The Solvay process is used to make sodium carbonate, NaThe Solvay process is used to make sodium carbonate, Na22COCO33, , a chemical that ranked 11th among all chemicals in annual a chemical that ranked 11th among all chemicals in annual production in 1986. The process begins with the passing of production in 1986. The process begins with the passing of ammonia and carbon dioxide through a solution of sodium ammonia and carbon dioxide through a solution of sodium chloride. This makes sodium bicarbonate and ammonium chloride. This makes sodium bicarbonate and ammonium chloride: Hchloride: H22O + NaCl + NHO + NaCl + NH33 + CO + CO22 ---------> NH ---------> NH44Cl + NaHCOCl + NaHCO33

How many grams of sodium bicarbonate could, in theory, be How many grams of sodium bicarbonate could, in theory, be

made from 5 moles of ammonia, NHmade from 5 moles of ammonia, NH33??

Mass-MoleUsing the equation: Pb(SO4)2 + 4 LiNO3 Pb(NO3)4 + 2 Li2SO4 , How many moles of lithium nitrate will be needed to make 250 grams of lithium sulfate, assuming that you have an adequate amount of lead (IV) sulfate to do the reaction?

Mass to Mass Problems

What mass of aluminum is produced by the decomposition of 5.0 kg of Al2O3?

Mole to Mole Problems

CO2 + 2 LiOH Li2CO3 + H2O

Given: 20 mol CO2

Unknown: X mol LiOH

20 mol X mol

20 mol CO2 × = mol LiOH

The MOLE TRAIN!!!!!!

Mole Train

How can we go from moles of one compound to mole of

another compound?

Use the mole ratio, Duh!

2 mol LiOH

1 mol CO2

40

How many moles of lithium hydroxide are required to react with 20 moles of carbon dioxide?

How many moles of water are produced in the complete combustion of 1.00 moles of glucose

according to the following reaction: C6H12O6 + 6O2 ----> 6CO2 + 6H2O

6 mole H2O

1.00 moles C6H12O6 X --------------------

1 moles C6H12O6

6.00 moles of water

What mass of H2SO4 can be formed from 5.0 moles of SO2 and an unlimited quantity of H2O and O2?

2SO2 + O2 + 2H2O ---- 2H2SO4

2 moles H2SO4 98 grams H2SO4

5.0 moles SO2 X --------------- X ----------------------

2 moles SO2 1 mole H2SO4

490 grams

The newly discovered element Takalahium (symbol Tak; molecular mass = 411 g/mol) combines with oxygen to form Takalahium Oxide. The unbalanced equation is:

Tak + O2 ---> Tak2O3 How many grams of Tak Oxide are formed when burning 8.00 moles of Tak?

2 mole Tak2O3 870 grams Tak2O3

8.00 moles Tak X --------------- X ----------------------

4 mole Tak 1 mole Tak2O3

3480 grams

A piece of zinc metal weighing 2.00 grams is placed in an aqueous solution of silver nitrate. How

many moles of silver can be recovered from this single replacement reaction?

• 1 Zn + 2 AgNO3 1 Zn(NO3)2 + 2 Ag 1 mole Zn 2 moles Ag

2.00 grams Zn X --------------- X ---------------------- 65.39 grams Zn 1 mole Zn

.061 moles

Mass- Mole ProblemMass- Mole ProblemThe octane present in gasoline burns according to the following equation: 2 C8H18 + 25 O2 ---------> 16 CO2 + 18 H2OHow many moles of CO2 are produced when 30 grams of octane react with an excess of oxygen?

1 mole C8H18 16 moles CO2

30 grams C8H18 X --------------- X ----------------------

114 grams C8H18 2 mole C8H18

2.10 moles

The formation of water from hydrogen and oxygen gas is: 2H2 (g) + O2 (g) ---> 2H2O (l). What mass of water will form from 12.0 grams of hydrogen and excess oxygen?

1 mole H2 2 mole H2O 18 grams H2O

12.0 grams H2 X --------------- X ------------------ X ----------------

2 grams H2 2 moles H2 1 mole H2O

108 grams

In the reaction: KClO3 + 5KCl + 6HNO3 --> 6KNO3 + 3Cl2 + 3H2O,

how many grams of KClO3 are required to prepare 10.0 g of Cl2?

1 mole Cl2 1 mole KClO3 122.55 grams KClO3

10 grams Cl2 X --------------- X ------------------ X -----------------------

70.9 grams Cl2 3 moles Cl2 1 mole KClO3

5.76 grams

Working a Stoichiometry Problem

6.50 grams of aluminum reacts with an excess of oxygen. How many grams of aluminum oxide are formed?

4 Al + 3 O2 2Al2O3

=6.50 g Al

? g Al2O3

1 mol Al

26.98 g Al 4 mol Al

2 mol Al2O3

1 mol Al2O3

101.96 g Al2O3

6.50 x 2 x 101.96 ÷ 26.98 ÷ 4 =

12.3 g Al2O3

Limiting Reactant Video Video

The The limiting reactantlimiting reactant is the reactant that is is the reactant that is consumed firstconsumed first,, limiting the amounts of limiting the amounts of products formed.products formed.

Analogy• You need to bake some cakes for the

school bake sale. The cake recipe calls for 2 cups of flour and 4 eggs. If you have 4 cups of flour and a dozen of eggs, how many cakes can you make?

2 cups flour 4 eggs

4 cups of flour X = 2 cakes

2 cups flour = 1 cake 4 eggs Which ingredient ran out first (limiting)?

Silicon dioxide is usually quite unreactive but reacts readily with hydrogen fluoride according to the following equation.

SiO2 + 4 HF SiF4 + 2 H2O

• If 2.0 mol of HF are exposed to 4.5 mol of SiO2, which is the limiting reactant?

4.5 mol SiO2

2.0 mol HF 1 mol SiO2

4 mol HF

Look at the balanced equation and mole-to-mole ratio

If 12.0 g CH4 and 24.0 g O2 react to form CO2 and H2O, how many grams of CO2 will be formed?

• 1 CH4 + 2 O2 1 CO2 + 2 H2O 1 mole CH4 2 mole O2 32 grams O2

12 grams CH4 X --------------- X ------------------ X -----------------------

16 grams CH4 1 mole CH4 1 mole O2

Need: 48 grams- O2 Limited: O2 will run out first 1 mole O2 1 mole CO2 44 grams CO2

24 grams O2 X --------------- X --------------- X -------------------

32 grams O2 2 moles O2 1 mole CO2

16.5 grams CO2

How do you know which one to use?

Practice Methane (CH4) reacts with O2 to form CO2 and water. If 30.0 grams of

CH4 and 64.0 grams of O2 are mixed and the reaction goes to completion, how many grams of the reactant "in excess" remain?

• 1 CH4 + 2 O2 1 CO2 + 2 H2O 1 mole O2 1 mole CH4 16 grams CH4

64 grams O2 X --------------- X ------------------ X --------------------

32 grams O2 2 mole O2 1 mole CH4

Will Use 16 grams CH4

Excess Remaining = 30.0 grams – 16 grams =

14 grams

Some rocket engines use a mixture of hydrazine, N2H4, and hydrogen peroxide, H2O2, as the propellant. The reaction is given by the following equation.

N2H4 + 2 H2O2 N2 + 4 H2O

a. Which is the limiting reactant in this reaction when 0.750 mol of N2H4 is mixed with 0.500 mol of H2O2?b. How much of the excess reactant, in moles, remains unchanged?c. How much of each product, in moles, is formed?

The black oxide of iron, Fe3O4, occurs in nature as the mineral magnetite. This substance can also be made in the laboratory by the reaction between red-hot iron and steam according to the following equation.

3 Fe + 4 H2O Fe3O4 + 4 H2

a. When 36.0 g of H2O is mixed with 167 g of Fe, which is the limiting reactant?

b. What mass in grams of black iron oxide is produced?

c. What mass in grams of excess reactant remains when the reaction is completed?

In the reaction PCl5 --> PCl3 + Cl2, 104.3 g of PCl5 are used, and 30.0 g of Cl2 are produced. What is the % yield of Cl2 in this reaction?

% Yield = Actual Yield (given in problem) X 100

Theoretical Yield (find with stoichiometry)

104.3 grams PCl5 X 1 mole PCl5 X 1 mole Cl2 X 70.9 grams Cl2 208.25 grams PCl5 1 mole PCl5 1 mole Cl2

Theoretical Yield= 35.5 grams

Actual Yield = 30.0 grams

Percent Yield = 30.0 grams Cl2 X 100

35.5 grams Cl2Ans: 84.5

%

Ans: 35.5

How many grams of CaF2 is formed

when 35.8mL of 0.678 M NaF is treated with excess of Ca(NO3)2(aq)?

M = 0.678

35.8 mL X __1 L_ X 0.678 mol X 1 mol CaF2 X 78g CaF2

1000mL 1L 2 mol NaF 1 mol

NaF + Ca(NO3)2 CaF2 + Na2(NO3)2

0.947 g CaF2

Determine which compound is limiting

The reaction needs 14.4g of AgNO3 But we only have 6.00g. The reaction will stop when AgNO3 is gone Now that you know which is the limiting reagent we can use it’s mass to solve for how many grams of Ag2CO3

The End!The End!The End!The End!The End!The End!