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Start-Up
What is the molar mass for Calcium hydroxide?A. 57.08 g/molB. 74.08 g/molC. 64.08 g/molD. 27 g/mol
Stoichiometry
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?
Example
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
AgNO3 + NaCl AgCl + NaNO3
2. Given and asked for
17.0g ?g
3. Moles of given
17.0g AgNO3 x 1 mol = 170 g
0.100 mol AgNO3
Mass-Mass Problem Cont.
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 AgCl14.4 g AgCl
AgNO3 + NaCl AgCl + NaNO3
Example #2
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
3Ca(OH)2 + 2H3PO4 Ca3(PO4)2 + 6HOH
2. Given & asked for
10.0 g? g
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 answer0.153 mol Ca(OH)2 x 74 g = 1 mol Ca(OH)2
11.3 g Ca(OH)2
4Na + O2 2Na2O1.44g ?g
1.44g x 1mol / 23g = 0.0626mol Na0.0626mol Na x 2Na2O / 4Na = 0.0313mol Na2O0.0313mol Na2O x 62g / 1mol = 1.94g Na1.94g Na22OOHow 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
?kg 4620g (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)(4.73kg) Pb(NOPb(NO33))22
What mass of sodium oxide is produced by the reaction of 1.44 g of sodium with oxygen?
2Li + 2H2O 2LiOH + H2
0.85g ?g0.85g Li x 1mol / 7g = 0.12mol Li0.12mol Li x 1H2 / 2Li = 0.060mol H2
0.060mol H2 x 2g / 1mol = 0.12g H0.12g H22 3.0g 3.0g LiOH 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) ?g192,000g C7H14 x 1mol / 98g = 1960mol C7H14
1960mol C7H14 x 14mol / 2mol = 13700mol H2O13700mol H2Ox 18g / 1mol = 247,000g H247,000g H22O O 658,000g O658,000g O22
What quantity of hydrogen gas is formed when 0.85 g of lithium reacts with water? How much lithium hydroxide is produced?
Classwork
P. 307, #1-4 Fe2O3 + 2Al 2Fe + Al2O3
P. 309, #1-4
Homework
P. 311, #1-7