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Start-Up

What is the molar mass for Calcium hydroxide?

A. 57.08 g/mol

B. 74.08 g/mol

C. 64.08 g/mol

D. 27 g/mol

Stoichiometry

- The molar relationship between all of the compounds in a balanced equation.
- Law of Conservation of Mass
- What is on the left (reactant side) must equal what is on the right (product side).

Ratio

- What is a molar ratio?
- The ratio is represented by the coefficient in front of the chemical formula.
- In stoichiometry, a molar ratio is the small, whole number ratio between each of the participants in a chemical reaction.
1N2 + 3H2 2NH3

The ratio of Nitrogen to Hydrogen to Ammonia is 1:3:2

Steps for Determining Molar Ratio

- Step 1: Write out the equation.
- Step 2: Balance the equation.
- Step 3: Determine the molar relationships

- Write and balance the equation for the reaction of Calcium hydroxide and Ammonium sulfate yields Calcium sulfate and ammonia and water.
- What is the mole ratio between each of the participants?

The Step-by-Step Process

- Write out the equation.
- Ca(OH)2(aq)+ (NH4)2SO4(aq) → CaSO4 + NH3(g) + H2O(l)

- Balance the Equation
- Ca(OH)2(aq)+ (NH4)2SO4(aq) → CaSO4 + 2NH3(g) + 2H2O(l)

- Determine the molar relationships
- 1:1:1:2:2

Another example

- Write and balance the reaction of sodium with water to yield sodium hydroxide and hydrogen gas.
- What are the ratios?
- 2Na(s) + 2H2O(l) → 2NaOH(aq) + H2(g)
- The ratio is 2:2:2:1

Now try this one

- Write and balance the equation for the reaction of ammonia with oxygen to yield nitric acid (HNO3) and water.
- NH3(g) + 2O2(g) → HNO3(aq) + H2O(l)
- The ratio is 1:2:1:1

The Key

- Stoichiometry means that if you know one piece of information about ONE compound in an equation, you can determine EVERYTHING else!!!!!
- If you have 3L of Nitrogen, how many liters of ammonia will you produce?
N2 + 3H2 2NH3

Think of it as a recipe

- Let’s look at that last reaction again.
- N2(g) + 3H2(g) 2NH3(g)

- If you start out with 1 mole of Nitrogen gas and 3 moles of Hydrogen gas, you will make 2 moles of Ammonia gas.
- It is important in industry to know the exact proportions of your ingredients so that you will not have excess waste in your product.

How many grams of silver chloride can be produced from the reaction of 17.0 g silver nitrate with excess sodium chloride solution?

1. Write the balanced equation

17.0g

?g

AgNO3 + NaCl AgCl + NaNO3

2. Given and asked for

3. Moles of given

17.0g AgNO3 x 1 mol =

170 g

0.100 mol AgNO3

Mass-Mass Problem Cont. reaction of 17.0 g silver nitrate with excess sodium chloride solution?

AgNO3 + NaCl AgCl + NaNO3

4. Moles asked for

0.100 mols AgNO3 x 1 mol AgCl =

1 mol AgNO3

0.100 mol AgCl

5. Convert your answer

0.100 mol AgCl x 144 g AgCl =

1 mol AgCl

14.4 g AgCl

Example #2 reaction of 17.0 g silver nitrate with excess sodium chloride solution?

How many grams of calcium hydroxide will be needed to react completely with 10.0 g of phosphoric acid (H3PO4) in a double displacement reaction?

1. Balanced equation reaction of 17.0 g silver nitrate with excess sodium chloride solution?

? g

10.0 g

3Ca(OH)2 + 2H3PO4 Ca3(PO4)2 + 6HOH

2. Given & asked for

3. Mols given

10.0 g H3PO4 x 1mol H3PO4 =

98.0 g

0.102 mol H3PO4

4. Mols asked for

0.102 mol H3PO4 x 3 mol Ca(OH)2 =

2 mol H3PO4

0.153 mol Ca(OH)2

5. Convert answer

0.153 mol Ca(OH)2 x 74 g =

1 mol Ca(OH)2

11.3 g Ca(OH)2

What mass of sodium oxide is produced by the reaction of 1.44 g of sodium with oxygen?

4Na + O2 2Na2O

1.44g ?g

1.44g x 1mol / 23g = 0.0626mol Na

0.0626mol Na x 2Na2O / 4Na = 0.0313mol Na2O

0.0313mol Na2O x 62g / 1mol = 1.94g Na2O

How many kg of lead (II) nitrate will be needed to react with sodium chromate to produce 4.62 kg of lead (II) chromate?

Pb(NO3)2 + Na2CrO4 2NaNO3 + PbCrO4

?kg4620g (4.62kg)

4620g x 1mol / 323g = 14.3mol PbCrO4

14.3mol PbCrO4 x 1mol / 1mol = 14.3mol Pb(NO3)2

14.3mol Pb(NO3)2 x 331g / 1mol = 4730g(4.73kg)Pb(NO3)2

What quantity of hydrogen gas is formed when 0.85 g of lithium reacts with water? How much lithium hydroxide is produced?

2Li + 2H2O 2LiOH + H2

0.85g?g

0.85g Li x 1mol / 7g = 0.12molLi

0.12mol Li x 1H2 / 2Li = 0.060molH2

0.060mol H2 x 2g / 1mol = 0.12g H2 3.0g LiOH

What mass of water is given off when 192 kg of C7H14 burn completely in air? How much oxygen is used?

2C7H14 + 21O2 14CO2 + 14H2O

192,000g (192kg)?g

192,000g C7H14 x 1mol / 98g = 1960mol C7H14

1960mol C7H14 x 14mol / 2mol = 13700mol H2O

13700mol H2Ox 18g / 1mol = 247,000g H2O 658,000g O2

Classwork lithium reacts with water? How much lithium hydroxide is produced?

- P. 307, #1-4
- Fe2O3 + 2Al 2Fe + Al2O3

- P. 309, #1-4

Homework lithium reacts with water? How much lithium hydroxide is produced?

- P. 311, #1-7

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