Download Unit 13 Stoichiometry (Theoretical)

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Unit 13 Stoichiometry (Theoretical)
THE MOLE – the amount of a substance that contains 6.02 x 1023 representative particles*
*representative particles = atoms (for elements), molecules (for covalent compounds), formula units (for ionic
compounds), ions
6.02 x 1023 or 602,213,673,600,000,000,000,000 is Avogadro’s number
MOLE CONVERSION FACTORS
1 mole = 6.02 x 1023 representative particles (atoms, molecules, formula units, ions)
1 mole = 22.4 L (of a gas at STP*)
1 mole = molar mass (in grams)
*STP = standard temperature (0°C) and pressure (1 atm)
SUBSCRIPTS – indicate the mole ratio of atoms or ions in a compound
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
Covalent molecules
o In 1 mole of H2O, there are 2 moles of hydrogen atoms and 1 mole of oxygen atoms
o In 1 mole of C6H12O6, there are 6 moles of C atoms: 12 moles of H atoms: 6 moles of O atoms
Ionic compounds
o In 1 mole of Ca(NO3)2 there are 1 mole of calcium ions and 2 moles of nitrate ions
o In 1 mole of K2O, the ion ratio is 2 mole K+1 ions: 1 mole of O-2 ions
COEFFICIENTS – indicate the mole ratio of species in a chemical reaction
2 H2 + 1O2  2 H2O

2 moles of hydrogen molecules: 1 mole of oxygen molecules: 2 moles of water molecules
2 Na + Cl2  2 NaCl + Energy

2 moles of sodium atoms: 1 mole of chlorine molecules: 2 moles of sodium chloride formula units
DIMENSIONAL ANALYSIS
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



Start with what you know (number, unit, and chemical formula). Write this value over 1 to make it
a fraction.
Use a conversion factor to get desired units. Write conversion factor as a fraction. Every
conversion factor must include NUMBER, UNIT, CHEMICAL FORMULA.
UNITS MUST CANCEL.
Solve. Answer should be a number and unit.
Verify that your answer is reasonable.
Round answer to reasonable number of sig figs.
Example: How many moles are in15.5 grams of carbon?
15.5 𝑔 𝐶
1
×
1 𝑚𝑜𝑙𝑒 𝐶
12.011 𝑔 𝐶
= 1.29 𝑚𝑜𝑙𝑒𝑠 𝐶
Example: How many molecules in 5.68 Liters of carbon dioxide gas?
5.68 𝐿 𝐶𝑂2
1
×
1 𝑚𝑜𝑙𝑒 𝐶𝑂2
22.4 𝐿 𝐶𝑂2
×
6.02 𝑥 1023 𝑚𝑜𝑙𝑒𝑐𝑢𝑙𝑒𝑠 𝐶𝑂2
1 𝑚𝑜𝑙𝑒 𝐶𝑂2
= 1.53 𝑚𝑜𝑙𝑒𝑐𝑢𝑙𝑒𝑠 𝐶𝑂2
Example: How many ions of bromine are in 2.63 grams of MgBr2?
2.63 𝑔 𝑀𝑔𝐵𝑟2
1 𝑚𝑜𝑙𝑒 𝑀𝑔𝐵𝑟2
2 𝑚𝑜𝑙𝑒𝑠 𝐵𝑟 −1 𝑖𝑜𝑛𝑠
×
×
= 0.0286 𝑚𝑜𝑙𝑒𝑠 𝐵𝑟 −1 𝑖𝑜𝑛𝑠
1
184.113 𝑔 𝑀𝑔𝐵𝑟2
1 𝑚𝑜𝑙𝑒 𝑀𝑔𝐵𝑟2
STOICHIOMETRY – using relationships between reactants and/or products in a chemical
reaction to determine desired quantitative data
Recipe Analogy
“Reaction”:
3 c. flour + 1 tsp. baking powder + 0.25 tsp. baking soda + 0.75 tsp. salt + 2 sticks of butter + 1.25 c. sugar +
0.25 c. cream cheese + 1 tsp. vanilla extract + 0.25 tsp. almond extract + 1 large egg  72 cookies
Conversion factors:
1 cup of flour = 120.3 grams of flour
1 stick of butter = 113.5 grams of butter = ½ cup of butter
1 cup of sugar = 198.4 grams of sugar
1 cup of cream cheese = 14.25 grams of cream cheese
1 dozen = 12 cookies
Example: How many grams of sugar will Betty Baker need to make 36 cookies?
36 𝑐𝑜𝑜𝑘𝑖𝑒𝑠
1.25 𝑐𝑢𝑝𝑠 𝑠𝑢𝑔𝑎𝑟
198.4 𝑔𝑟𝑎𝑚𝑠 𝑠𝑢𝑔𝑎𝑟
×
×
= 124 𝑔𝑟𝑎𝑚𝑠 𝑠𝑢𝑔𝑎𝑟
1
72 𝑐𝑜𝑜𝑘𝑖𝑒𝑠
1 𝑐𝑢𝑝 𝑠𝑢𝑔𝑎𝑟
Example: How many teaspoons of almond extract will Charlie need if he wants to use up all 1758 grams of
butter in his refrigerator?
1758 𝑔𝑟𝑎𝑚𝑠 𝑏𝑢𝑡𝑡𝑒𝑟
1 𝑠𝑡𝑖𝑐𝑘 𝑏𝑢𝑡𝑡𝑒𝑟
0.25 𝑡𝑠𝑝. 𝑎𝑙𝑚𝑜𝑛𝑑 𝑒𝑥𝑡𝑟𝑎𝑐𝑡
×
×
= 1.94 𝑡𝑠𝑝. 𝑎𝑙𝑚𝑜𝑛𝑑 𝑒𝑥𝑡𝑟𝑎𝑐𝑡
1
113.5 𝑔𝑟𝑎𝑚𝑠 𝑏𝑢𝑡𝑡𝑒𝑟
2 𝑠𝑡𝑖𝑐𝑘𝑠 𝑏𝑢𝑡𝑡𝑒𝑟
Example: How many grams of cream cheese will Carrie the Cook need if she has 2000. grams of flour to use
for her sugar cookies?
2000. 𝑔 𝑓𝑙𝑜𝑢𝑟
1 𝑐𝑢𝑝 𝑓𝑙𝑜𝑢𝑟
0.25 𝑐𝑢𝑝𝑠 𝑐𝑟𝑒𝑎𝑚 𝑐ℎ𝑒𝑒𝑠𝑒
14.25 𝑔 𝑐𝑟𝑒𝑎𝑚 𝑐ℎ𝑒𝑒𝑠𝑒
×
×
×
= 19.7 𝑡𝑠𝑝. 𝑎𝑙𝑚𝑜𝑛𝑑 𝑒𝑥𝑡𝑟𝑎𝑐𝑡
1
120.3 𝑔 𝑓𝑙𝑜𝑢𝑟
3 𝑐𝑢𝑝𝑠 𝑓𝑙𝑜𝑢𝑟
1 𝑐𝑢𝑝 𝑐𝑟𝑒𝑎𝑚 𝑐ℎ𝑒𝑒𝑠𝑒
Example: Based on the following reaction, how many grams of S2Cl2 will be formed from 15.0 g Cl2? (Balance
equation first!)
Cl2 (g) + 2 S (l)  S2Cl2 (l)
Example: Based on the following reaction, how many molecules of chlorine are required to form 100. grams of
sodium chloride? (Balance equation first!)
2 Na + Cl2  2 NaCl + energy
This is Avogadro’s
number, which converts
moles to molecules.
𝟏𝟎𝟎. 𝒈𝒓𝒂𝒎𝒔 𝑵𝒂𝑪𝒍
𝟏 𝒎𝒐𝒍𝒆 𝑵𝒂𝑪𝒍
𝟏 𝒎𝒐𝒍𝒆 𝑪𝒍𝟐
𝟔. 𝟎𝟐 𝒙 𝟏𝟎𝟐𝟑 𝒎𝒐𝒍𝒆𝒄𝒖𝒍𝒆𝒔 𝑪𝒍𝟐
×
×
×
= 𝟓. 𝟏𝟓 𝒙 𝟏𝟎𝟐𝟑 𝒎𝒐𝒍𝒆𝒄𝒖𝒍𝒆𝒔 𝑪𝒍𝟐
𝟏
𝟓𝟖. 𝟒𝟒𝟑 𝒈 𝑵𝒂𝑪𝒍
𝟐 𝒎𝒐𝒍𝒆𝒔 𝑵𝒂𝑪𝒍
𝟏 𝒎𝒐𝒍𝒆 𝑪𝒍𝟐
Example: Based on the following reaction, how many grams of KClO3 are required to produce 9.00 L of O2 at
STP?
2 KClO3  2 KCl + 3 O2
This is the
molar mass of
the unknown,
which converts
moles to grams.
𝟗. 𝟎𝟎 𝑳 𝑶𝟐
𝟏 𝒎𝒐𝒍𝒆 𝑶𝟐
𝟐 𝒎𝒐𝒍𝒆𝒔 𝑲𝑪𝒍𝑶𝟑
𝟏𝟐𝟐. 𝟓𝟒𝟖 𝒈 𝑲𝑪𝒍𝑶𝟑
×
×
×
= 𝟑𝟐. 𝟖 𝒈 𝑲𝑪𝒍𝑶𝟑
𝟏
𝟐𝟐. 𝟒 𝑳 𝑶𝟐
𝟑 𝒎𝒐𝒍𝒆𝒔 𝑶𝟐
𝟏 𝒎𝒐𝒍𝒆 𝑲𝑪𝒍𝑶𝟑
This is molar volume,
which converts liters to
moles.
Example: How many liters of oxygen gas are produced if 7.96 moles of potassium chlorate react completely?
2 KClO3  2 KCl + 3 O2
𝟕. 𝟗𝟔 𝒎𝒐𝒍𝒆𝒔 𝑲𝑪𝒍𝑶𝟑
𝟑 𝒎𝒐𝒍𝒆 𝑶𝟐
𝟐𝟐. 𝟒 𝑳 𝑶𝟐
×
×
= 𝟐𝟔𝟕 𝑳 𝑶𝟐
𝟏
𝟐 𝒎𝒐𝒍𝒆𝒔 𝑲𝑪𝒍𝑶𝟑
𝟏 𝒎𝒐𝒍𝒆 𝑶𝟐
Name ________________________________________
Period _________
Unit 13 Practice Sheet
1. What is the molar mass of Al2O3?
2. How many grams are equivalent to 2.4 x 1023 formula units of aluminum oxide? (ans. 40.6 g Al2O3)
3. What is the ratio of aluminum ions to oxygen ions in Al2O3?
4. How many liters of water are equal to 39.5 grams of water?
5. How many moles of water are equal to 7.35 x 1030 molecules of water?
6. What is the ratio of hydrogen atoms to oxygen atoms in a mole of water molecules?
7. Al (s) + O2 (g)  Al2O3 (s)
a. Balance the above equation.
b. Write all 6 mole ratios that can be derived from the balanced equation.
c. How many moles of aluminum are needed to form 3.7 moles of Al2O3?
d. How many moles of oxygen are required to react completely with 14.8 moles of aluminum?
e. How many moles of Al2O3 are formed when 0.78 moles of O2 reacts with aluminum? (Ans. 0.52
mol Al2O3)
f. How many grams of aluminum are required to produce 98.6 grams of aluminum oxide?
g. How many liters of oxygen are required to react completely with 75.8 grams of aluminum?
h. How many formula units of aluminum oxide are produced if 6.42 moles of oxygen gas react?
8. CaC2 (s) + H2O (l)  C2H2 (g) + Ca(OH)2 (aq)
a. Balance the above equation.
b. How many grams of acetylene (C2H2) are produced by adding water to 5.00 grams of CaC2?
(ans. 2.03 g C2H2)
c. How many moles of CaC2 are needed to react completely with 49.0 grams of water?
d. How many liters of acetylene are produced if 128 grams of CaC2 are used?
e. If 7.95 x 1027 molecules of acetylene are produced, how many ions of hydroxide are also
produced?
f. What is the mole ratio between water and calcium hydroxide?
9. Methanol (CH4O) is used in the production of many chemicals. Methanol is made by reacting carbon
monoxide and hydrogen at high temperature and pressure, according to the following chemical
equation:
CO (g) + H2 (g)  CH4O (g)
a. Balance the chemical equation showing the synthesis of methanol.
b. How many molecules of hydrogen are needed to produce 25.0 grams of CH4O?
c. How many molecules of carbon monoxide are needed to produce 50.0 grams of methanol?
(ans. 9.39 x 1023 molecules CO)