Investigation 11A Stoichiometry

2 Investigation 11A: Stoichiometry If your doctor did not tell you how much of a medication you need to take, you could take too little and the medicine would not work. But if you take too much, it could cause severe consequences. How do you know how much of a chemical is necessary for a reaction to occur?

3 1.Put an empty cup on the balance and zero it. Measure 10.0 g of baking soda in the cup. Record the measured mass in Table 1. 2.Put another empty cup on the balance and zero it. Measure 30.0 g of vinegar in the cup. Record the measured mass in Table 1. 3.Add the masses of vinegar and baking soda. Record the sum in Table 1 (row 3). Investigation 11A: Stoichiometry Part 1: The reaction

4 Investigation 11A: Stoichiometry 4.Slowly pour the vinegar into the baking soda. Pouring it too fast might cause the bubbling to overflow! Wait until the bubbling has stopped and record the mass. Part 1: The reaction

5 Investigation 11A: Stoichiometry a.What evidence did you observe that indicated a chemical reaction was taking place? b.Explain the difference in the total mass before and after mixing. c.Do you see any baking soda that has not reacted? Part 2: What happened?

6 Investigation 11A: Stoichiometry a.The balanced reaction is written on the first line of the chart above. Calculate the formula mass of each of the products and reactants. Baking soda (sodium bicarbonate) Acetic acid (acid in vinegar) Part 3: Understanding the reaction

7 Investigation 11A: Stoichiometry b.One of the products is a gas. Which one? Will this product’s mass contribute to the mass as measured on the balance after the reaction has finished? Why or why not? c.On the second line, write down the mass of the baking soda and vinegar you added. Baking soda (sodium bicarbonate) Acetic acid (acid in vinegar) Part 3: Understanding the reaction

8 Investigation 11A: Stoichiometry d. Vinegar is 5% acetic acid (HC 2 H 3 O 2 ) by mass. Multiply by 0.05 to get the actual mass of acetic acid. e.Use the formula masses to calculate the number of moles of NaHCO 3 and HC 2 H 3 O 2. Part 3: Understanding the reaction

9 Investigation 11A: Stoichiometry f.How many moles of CO 2 were produced? g.Use the formula mass to calculate the mass of CO 2 produced Part 3: Understanding the reaction

10 Investigation 11A: Stoichiometry a.How many grams of CO 2 were produced in the reaction? b.How does the answer to Part a explain the mass measurement you found at the end of the experiment? c.Did all the baking soda react? How do you know? d.Did all the acetic acid react? How do you know? e.What was the limiting reactant in this experiment? How do you know? Part 4: Stop and think

11 Investigation 11A: Stoichiometry To make an efficient reaction, there should not be any reactants left over. Steps a–d Use this chart to calculate how many grams of vinegar need to be added to react with all the baking soda Part 5: An efficient reaction

12 Investigation 11A: Stoichiometry 1.Measure out 10.0 g of baking soda in one cup. 2.Measure out the required amount of vinegar (from your calculations) in the other cup. 3.Write down the total mass before you mix the reactants. Part 6: Test your hypothesis

13 Investigation 11A: Stoichiometry Calculate the mass of CO 2 produced. How does this number match your experiment? Part 6: Test your hypothesis

14 Investigation 11A: Stoichiometry Steps a–e Using stoichiometry, calculate how much baking soda and vinegar you would need to make 10.0 g of CO Part 7: Using stoichiometry

15 Investigation 11A: Stoichiometry Perfect combustion of octane: If the fuel is burned perfectly, the reaction that occurs in a gasoline engine would only produce carbon dioxide and water. Part 8: Applying the principle

16 Investigation 11A: Stoichiometry Perfect combustion of octane: a.Calculate the formula mass for octane. b.Suppose a car uses 25 gallons of gasoline in a week. The density of gasoline is about 2,900 g/gallon. Calculate the mass in grams of 25 gallons of gasoline. Part 8: Applying the principle

17 Investigation 11A: Stoichiometry Perfect combustion of octane: c. Assume gasoline is pure octane. How many moles does this quantity represent? d. How many moles of CO 2 are created for every 2 moles of gasoline burned? e. Calculate the mass of CO 2 released from the perfect combustion of 25 gallons of gasoline. Part 8: Applying the principle