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PERCENT POTASSIUM CHLORATE IN A MIXTURE - Worksheet
This lab will introduce the concept of reaction stoichiometry. We will use the mole ratios in a balanced
chemical equation to calculate the amount of potassium chlorate in a sample by measuring the amount of
molecular oxygen that is produced when it undergoes a decomposition reaction. A difference in chemical
properties will lead to a change which can be measured in the lab, which will allow the composition of the
original sample to be determined.
Stoichiometry is the study of the numerical relationships in chemical formulas and reactions. Knowing the
stoichiometry of a formula allows us to relate moles and grams for particular reactants or products (i.e., that 1
mole of H2O weighs 18.02 g). Knowing the stoichiometry of a reaction allows us to relate amounts of different
substances to each other, and allows us to predict how much of the product(s) will be formed, or how much of
the reactant(s) will be needed.
Since moles combine in the same ratio that atoms, molecules, or formula units do, the coefficients in a balanced
chemical reaction specify the relative amounts in moles of each of the substances involved in the reaction.
For example, consider the reaction between hydrogen and oxygen to make water:
2 H2(g) + O2(g) → 2 H2O(g)
The coefficients of this reaction can be interpreted in two different ways:
react with
this many
molecules
of O2
This many
molecules
of H2
to make
this many
molecules
of H2O
2 H2(g) + 1 O2(g) → 2 H2O(g)
This many
moles
of H2
react with
this many
moles
of O2
to make
this many
moles
of H2O
This means that the coefficients can be used as conversion factors to relate the number of moles of one
chemical to the number of moles of another chemical:
2 moles of H2 = 1 mole of O2
2 moles of H2 = 2 moles of H2O
1 mole of O2 = 2 moles of H2O
or, if we rewrite these relationships as ratios:
2 mol H 2
1 mol O 2
2 mol H 2
2 mol H 2 O
1 mol O 2
2 mol H 2 O
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(The reciprocals of these relations are of course also valid ratios.) These relationships are true only for this
particular balanced equation. A different chemical equation will have its own unique set of relationships,
derived from the coefficients in that reaction.
For example, suppose we have 32.0 grams of O2 in the above reaction. We can use the balanced equation to
determine how many grams of H2 will be needed, and how many grams of H2O will be produced:
Convert g O2 to mol O2:
32.0 g O 2 ×
1 mol O 2
= 1.00 mol O 2
32.00 g O 2
Convert mol O2 to mol H2:
coefficient that we want
↓
2 mol H 2
1.00 mol O 2 ×
= 2.00 mol H 2
1 mol O 2
↑
coefficient that we started with initially
Convert mol H2 to g H2:
2.00 mol H 2 ×
2.02 g H 2
= 4.04 g H 2
1 mol H 2
or, we can put everything together in a single calculation,
32.0 g O 2 ×
1 mol O 2
2 mol H 2 2.02 g H 2
×
×
= 4.04 g H 2
32.00 g O 2 1 mol O 2 1 mol H 2
How many grams of water will be formed?
32.0 g O 2 ×
1 mol O 2
2 mol H 2 O 18.02 g H 2 O
×
×
= 36.0 g H 2 O
32.00 g O 2 1 mol O 2
1 mol H 2 O
In this experiment, the number of moles of O2 can be used to calculate the number of moles of KClO3 in the
original sample, and therefore the number of grams of KClO3 in the sample. From the mass of KClO3 and the
mass of the sample, the percentage of KClO3 in the sample can then be determined.
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Name:
Percent Potassium Chlorate in a Mixture - Worksheet
Write and/or balance the following equations. Remember the seven diatomic elements! Use the mole ratios
from the balanced equations to solve the following problems. Show your work in all steps for full credit and
make sure you use significant figures on all problems.
1. Potassium chlorate decomposes into potassium chloride and oxygen gas – Part I
Balanced Equation:
2. How many moles of oxygen are produced when 3.0 moles of potassium chlorate
decompose completely?
3. How many moles of potassium chlorate are needed to produce 11.7 moles of oxygen gas?
4. Butane (C4H10) undergoes combustion.
Balanced Equation:
_____ C4H10(l) + _____ O2(g) → _____ CO2(g) + _____ H2O(l)
5. How many moles of butane are needed to create 3.7 moles of water?
6. How many grams of CO2 are produced when 88 g of O2 are reacted with an excess of
butane?
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7. Water decomposes into hydrogen gas and oxygen gas by electrolysis.
Balanced Equation:
8. How many grams of hydrogen will be produced when 6.0 moles of oxygen are produced?
9. How many grams of water are required to produce 9.00 grams of hydrogen?
10. Ammonium dichromate decomposes into gaseous water, gaseous nitrogen and solid
chromium(III) oxide.
Balanced Equation:
11. How many grams of ammonium dichromate are required to produce 34.0 g of
chromium(III) oxide?
12. How many total grams of gas are created when 454 g (1 pound) of ammonium dichromate
is allowed to decompose?
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13. Cobalt(II) chloride reacts with fluorine in a single replacement reaction to produce cobalt(II)
fluoride and chlorine gas.
Balanced Equation:
_____ CoCl2 + _____ F2 à _____ CoF2 + _____ Cl2
14. How many grams of fluorine are required to produce 290.8 g of cobalt(II) fluoride?
15. Solid iron(III) oxide reacts with hydrogen gas to form iron and water.
Balanced Equation:
16. How many grams of iron are produced when 450. grams of iron(III) oxide are reacted?
17. An impure sample of iron(III) oxide measuring 112.1 g reacts with an excess of hydrogen
gas, and 54.0 g of pure iron is isolated. Assuming the hydrogen gas doesn’t react with the
impurities, how much iron(III) oxide was present in the original sample? What is the
percent iron(III) oxide in the original sample?
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18. Potassium chlorate decomposes into potassium chloride and oxygen gas – Part II
Balanced Equation:
19. A 2.220 g of impure potassium chlorate is heated, and 1.700 g of solid material remains.
How many grams of oxygen were lost upon heating this reaction?
20. How many moles of oxygen were lost upon heating?
21. How many moles of potassium chlorate were present in the original mixture?
22. How many grams of potassium chlorate were present in the original mixture?
23. What percentage of the original mixture consisted of potassium chlorate?