AP Chemistry Lab
Stoichiometry
Name _____________________
Objective: Determine the mass relations in the chemical formula of potassium chlorate and use the
results to analyze a potassium chlorate-potassium chloride mixture.
Apparatus:
balance, Bunsen burner, small test tubes, ring stand, clamp, goggles
Chemicals:
potassium chlorate, potassium chloride, manganese dioxide
Reaction:
2 KClO3 
2 KCl + 3 O2
CAUTION: Potassium chlorate is a powerful oxidizing agent. It must not be mixed with reducing agents
such as sulfur or paper. Any spillage should be flushed down the drain with plenty of water.
Introduction
Stoichiometry concerns mass relations in chemical formulas and chemical reactions. The word
stoichiometry is derived from the Greek stoichein (“element”) and metron (“measure”). The quantitative
analysis of chemical formulas and reactions begins with proper use of stoichiometric data. This lab will
test your basic knowledge of this essential tool.
Pre-Lab:
1. Determine the molar masses of each substance in the equation above.
2. 1.678 g of a postassium chloride/potassium chlorate mixture is heated and it is determined that 0.879
g of potassium chlorate were in the mixture. Calculate the percent by mass of potassium chlorate.
Procedures
Part A Decomposition and analysis of potassium chlorate
1. To a clean, dry, small test tube add a pinch of manganese dioxide.
2. Mass the tube to 0.001 grams. Use a 250 mL beaker and zero its mass then add the tube.
3. Add approximately 1 g of dry potassium chlorate, tap gently to mix, then mass.
4. Clamp the tube to a ring stand at an angle of 45o and away from fellow students.
5. Heat gently with the Bunsen burner until the solid melts, then increase to a strong heat for several
minutes.
6. Allow the tube to cool, then mass.
Part B Analysis of a potassium chlorate-potassium chloride mixture
1. To a clean, dry, small test tube add a pinch of manganese dioxide.
2. Mass the tube to 0.001 grams.
3. Add approximately 1 g of the potassium chlorate-potassium chloride mixture, tap gently to mix, then
mass.
4. Clamp the tube to a ring stand at an angle of 45o and away from fellow students.
5. Heat gently with the Bunsen burner until the solid melts, then increase to a strong heat for several
minutes.
6. Allow the tube to cool, then mass.
Raw Data Part A
Mass of Test Tube + MnO2
Mass of TT +MnO2+ KClO3
Cooled TT (MnO2 + KCl)
Raw Data Part B
Mass of Test Tube + MnO2
Mass of TT +MnO2+ KCl/KClO3 mixture
Cooled TT (MnO2 + KCl)
Calculated Data Part A
Mass of Oxygen
Moles of Oxygen
Mass of KCl
Moles of KCl
Moles of K
Moles of Cl
Empirical formula
Calculated Data Part B
Mass of Oxygen
Moles of Oxygen
Moles of KCl
Mass of KCl
Mass of Mixture
Percentage of KClO3 in mixture
Calculations
Many of these calculations will depend on stoichiometry. You should be using the mole ratios provided
by the subscripts in the formulas of the substances. You will not use the coefficients from the equation.
Part A Decomposition and analysis of potassium chlorate
1. What was the mass of oxygen lost and how many moles does this represent?
2. What is the mass of potassium chloride (KCl) residue and how many moles does this represent?
3. How many moles of potassium atoms are present in the original sample?
4. How many moles of chloride atoms are present in the original sample?
5. Determine the empirical formula of potassium chlorate.
Part B Analysis of a potassium chlorate-potassium chloride mixture
6. What was the mass of oxygen lost and how many moles does this represent?
7. How many moles of potassium chlorate (KClO3) decomposed? What mass does this represent?
8. Determine the mass of the mixture you analyzed.
9. Determine the percentage by weight of potassium chlorate in the unknown mixture.