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A.P. Chemistry

Determining the Ratio of Moles of Reactants

Pre-Lab Questions 1. Compare the total mass of the reactants in a chemical reaction with the total mass of the products. 2. What natural law is demonstrated when a chemical equation is balanced? 3. What information do the coefficients in a balanced chemical equation provide? Background Information This experiment will explore the relationship between a balanced chemical equation and the ratio of moles of reactants in a chemical reaction. Although finding the ratio of moles of reactants would be easy by simply balancing the equation, this ratio will be verified by the data from the experiment. The method of continuous variations will be used to determine the ratio of moles of the reactants. This will be done by running a number of trials varying the number of moles of each reactant, but keeping the total number of moles of reactants the same. The trial that shows the maximum amount of product is closest to the correct ratio. By graphing the amounts of reactants vs. the amount of product, the correct ratio can be determined. The quantity that will be measured in this experiment will be the volume of carbon dioxide gas, CO2(g), produced. Materials Pneumatic trough 125 mL Erlenmeyer flask rubber tubing (2 ­ 60 cm long each) 3" piece of glass tubing electronic balance, ±0.001 g 50 mL graduated cylinder 250 mL graduated cylinder weighing dishes spatula #5 one-hole stopper 0.1 M H2SO4(aq) 0.1 M NaHCO3(aq)

Procedure 1. Put on your lab apron and safety goggles. 2. Set up the pneumatic trough, 250 mL graduated cylinder, Erlenmeyer flask and tubing as shown in the diagram.

3. Put 25 mL of 0.1 M H2SO4 in the Erlenmeyer flask. 4. Add 65 mL of 0.1 M NaHCO3 solution and firmly stopper the flask. 5. Carefully swirl the flask and continue until bubbles no longer form in the inverted graduated cylinder. (If a magnetic stirrer is available, it can be used to constantly stir the reaction). 6. Record the volume of CO2 gas produced. 7. Repeat the experiment using different amount of reactants as instructed in the following table.

8. Plot results on a graph put mL of reactants on the x-axis and volume of CO2 gas produced on the y-axis.

A.P. Chemistry

Determining the Ratio of Moles of Reactants ­ Lab Report

A.P. Chemistry

Determining the Ratio of Moles of Reactants ­ Lab Report

Analysis 1. From the data and graph, determine the ratio of moles of H2SO4 to NaHCO3. Explain how this method is used to find the mole ratio.

2. For each trial, identify which reactant is in excess and which one is the limiting reagent.

3. What other physical properties could be measured to determine the number of moles in a chemical reaction?

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Microsoft Word - mole ratio lab

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Microsoft Word - mole ratio lab