This document discusses Universal Children's Day, which is observed annually on November 20. In 1954, the United Nations General Assembly recommended that countries introduce an annual event to encourage understanding between children worldwide and promote children's welfare. While countries could choose their own date, many opted to observe it on November 20th to respect this UN recommendation. Universal Children's Day aims to improve children's lives globally through international cooperation and understanding.

1. Name: ……………………………………
Grade: …………10………………
Subject: Chemistry
Date: ……………….
Chapter 15 : Stoichiometry Practice Problems
Be sure to balance all equations before you start calculating
Rally coach :
1) Lithium hydroxide reacts with hydrobromic acid to produce lithium bromide and water. If
you start with 10 grams of lithium hydroxide, how many grams of lithium bromide will be
produced? LiOH + HBr  LiBr + H2O
2) Ethylene (C2H4 ) reacts with oxygen gas to produce carbon dioxide and water. If you start
with 45 grams of ethylene, how many grams of carbon dioxide will be produced?
C2H4 + 3 O2  2 CO2 + 2 H2O
3) Be + 2 HCl  BeCl2 + H2
My theoretical yield of beryllium chloride was 10.7 grams. If my actual yield was 4.5 grams,
what was my percent yield?

2. 4) Given the equation: HCl + Na2SO4  NaCl + H2SO4
If you start with 20 grams of hydrochloric acid, how many grams of sulfuric acid will be
produced?
5) Given the following equation: LiOH + KCl  LiCl + KOH
a. I began this reaction with 20 grams of lithium hydroxide. What is my theoretical
yield of lithium chloride?
b. I actually produced 6 grams of lithium chloride. What is my percent yield?
6) Given the following equation: C3H8 + O2  CO2 + H2O
a. If I start with 5 grams of C3H8, what is my theoretical yield of water?
b. I got a percent yield of 75%. How many grams of water did I make?
7) Given the reaction: NaCl + CaO  CaCl2 + Na2O
What is my theoretical yield of sodium oxide if I start with 20 grams of calcium oxide?

3. 8) FeBr2 + 2 KCl  FeCl2 + 2 KBr
a. What is my theoretical yield of iron (II) chloride if I start with 34 grams of iron (II)
bromide?
b. What is my percent yield of iron (II) chloride if my actual yield is 4 grams?
9) TiS + H2O  H2S + TiO
What is my percent yield of titanium (II) oxide if I start with 20 grams of titanium (II)
sulfide and my actual yield of titanium (II) oxide is 22 grams?
10) U + 3 Br2  UBr6
What is my actual yield of uranium hexabromide if I start with 100 grams of uranium and
250 grams of bromine, and get a percent yield of 83% ?
11) Sulfur dioxide can be produced in the laboratory by the reaction of hydrochloric acid and a
sulfite salt such as sodium sulfite. (Na2SO3 + 2HCl → 2NaCl + SO2 + H2O) What mass
of SO2 can be made from 25.0 g or Na2SO3 and 22.0 g of HCl?
Name: grade: date:

4. Mole & Mass Conversions
1. What is the mass (in grams) of 1.00 moles of copper atoms?
1.00mol Cu x 63.5 g Cu = 63.5g Cu
1 mol Cu
2. How many moles are 4.00g of helium atoms?
4.00g He x 1 mol He = 1.00 mol He
4.00 g He
3. What is the mass of 3.56 moles of zinc?
3.56mol Zn x 65.4 g Zn = 233g Zn
1 mol Zn
4. What is the mass of 1.00 moles of water molecules?
1.00mol H2O x 18.0 g H2O = 18.0g H2O
1 mol H2O
5. How many moles are found in 7.95g of lithium chloride?
7.95g LiCl x 1 mol LiCl = 0.188 mol LiCl
42.4 g LiCl
6. What is the mass of 4.50mol of aluminum chloride?
4.50mol AlCl3 x 134 g AlCl3= 603g AlCl3
1 mol AlCl3
7. Convert 250g of calcium hydroxide into moles.
250g Ca(OH)2 x 1 mol Ca(OH)2 = 3.37 mol Ca(OH)2
74.1 g Ca(OH)2
8. You are given 365g of sugar (C6H12O6)
a) How many moles would you have?
365g C6H12O6 x 1 mol C6H12O6= 2.03 mol C6H12O6

5. Answer Key
1) LiOH + HBr  LiBr + H2O
If you start with ten grams of lithium hydroxide, how many grams of lithium bromide will
be produced? 36.3 grams
2) C2H4 + 3 O2  2 CO2 + 2 H2O
If you start with 45 grams of ethylene (C2H4), how many grams of carbon dioxide will be
produced? 141.4 grams
3) 2 HCl + Na2SO4  2 NaCl + H2SO4
If you start with 20 grams of hydrochloric acid, how many grams of sulfuric acid will be
produced? 26.9 grams
4) Given the following equation: LiOH + KCl  LiCl + KOH
a. I began this reaction with 20 grams of lithium hydroxide. What is my theoretical
yield of lithium chloride? 35.5 grams
b. I actually produced 6 grams of lithium chloride. What is my percent yield? 16.9%
5) Given the following equation: C3H8 + 5 O2  3 CO2 + 4 H2O
a. If I start with 5 grams of C3H8, what is my theoretical yield of water? 8.2 grams
b. I got a percent yield of 75%. How many grams of water did I make? 6.1 grams
6) Be + 2 HCl  BeCl2 + H2
My theoretical yield of beryllium chloride was 10.7 grams. If my actual yield was 4.5
grams, what was my percent yield? 42.1 %
7) Given the reaction: 2 NaCl + CaO  CaCl2 + Na2O
What is my theoretical yield of sodium oxide if I start with 20 grams of calcium oxide?
22.1 grams
8) FeBr2 + 2 KCl  FeCl2 + 2 KBr
a. What is my theoretical yield of iron (II) chloride if I start with 34 grams of iron (II)
bromide? 20.0 grams of FeCl2
b. What is my percent yield of iron (II) chloride if my actual yield is 4 grams? 20 %
9) TiS + H2O  H2S + TiO
What is my percent yield of titanium (II) oxide if I start with 20 grams of titanium (II)
sulfide and my actual yield of titanium (II) oxide is 22 grams? 137.5 % (theoretical yield is
16.0 grams—trick question; you should know that 100% is the highest yield possible)
10) U + 3 Br2  UBr6
What is my actual yield of uranium hexabromide if I start with 100 grams of uranium and
250 grams of bromine, and get a percent yield of 83% ? 250 grams UBr6

6. 11) Sulfur dioxide can be produced in the laboratory by the reaction of hydrochloric acid and a
sulfite salt such as sodium sulfite. (Na2SO3 + 2HCl → 2NaCl + SO2 + H2O) What mass of
SO2 can be made from 25.0 g or Na2SO3 and 22.0 g of HCl? 11.3 grams SO2

7. Universal Children's Day
On December 14, 1954, the United Nations General Assembly recommended
that all countries should introduce an annual event from 1956 known as
Universal Children's Day to encourage understanding between children all
over the world and promoting the welfare of children.
It was recommended that individual countries should choose an appropriate
date for this occasion.
Many of the countries respected this recommendation and the Universal
Children's Day has since been annually observed on November 20.