Experiment #1 / Unit 5
A Recipe for Salt and Bubbles
Introduction:
We have been learning about stoichiometry and how balanced chemical
equations allow us to relate and find amounts of reactants and products in a
chemical reaction. In this experiment, we will examine the stoichiometry of a
common household chemical reaction.
In most recipes for baked goods, sodium bicarbonate (NaHCO 3) is an
essential ingredient. Without it, cakes and cookies would not "rise". When an
acidic substance such as sour cream, buttermilk, vinegar, lemon juice, etc. is
added to baking soda, bubbles of carbon dioxide are produced.
NaHCO3
+
sodium bicarbonate
HA
acid

H2O
+
CO2
+
NaA
salt
This release of gas is what causes the cake to increase in size and become light
and fluffy. We will carry out the reaction of baking soda with an acid to examine
the stoichiometry of this chemical reaction. By measuring the masses of the solid
reactants and products, we will be able to determine the mole relationships
between the solid reactant and product and compare our results to what the
balanced equation tells us should happen. If we know the masses (and therefore
the moles) of the reactants we start with, we can use the "recipe" of the balanced
equation to predict how much of each product will be made before we even carry
out the reaction. We will make such a prediction (called the theoretical yield) and
compare our results to the prediction (% yield).
Percent yield = experimental yield =
what you recovered x 100
theoretical yield
max. predicted by the equation
Practice Problem (optional):
1. In an experiment, a reaction is carried out in which a solution of barium
chloride is mixed with a solution of silver nitrate to produce a white
precipitate. The mass of the reactant BaCl2 is found to be 10.2 g. The
precipitate is collected, dried, and found to have a mass of 14.5 g.
a. Write the balanced equation for the reaction of barium chloride with silver nitrate
and predict the theoretical mole ratio of silver chloride to barium chloride and the
amount of precipitate that could have been produced. (mol ratio = 2, 14.0 g AgCl)
b. Calculate the experimental mole ratio of silver chloride to barium chloride. (2.06)
c. Calculate the percent error for the experiment as reflected by the mole ratio. (3% error)
d. Calculate the percent yield. (104% yield)
Procedure:
1. Measure the mass of a clean, dry evaporating dish and watch glass.
2. Place the dish alone on the balance and press re-zero. Add NaHCO3 until
you have about 1.5xx g (you must record it accurately).
3. Obtain 6 mL of 6 M HCl in a graduated cylinder. Add the acid with a
dropper until all the baking soda has reacted, but do not add any excess
acid because it will all have to be evaporated. You will know it has all
Cary Academy
Chemistry I
W.G. Rushin
1
reacted when you can add a drop of acid and no bubbles appear. Any acid
that you do not use can be returned to the stock beaker. Test the gas
produced by lowering a lit wooden splint into the dish.
4. Set up a ringstand. Place the evaporating dish on the wire gauze with the
watch glass covering the dish, but allowing steam to escape.
5. Heat the dish with a low flame until only a dry solid remains. Avoid
overheating because it will cause the contents to spatter. Once the
contents of the dish are dry, you will need to dry the water droplets on the
underside of the watch glass. Using tongs carefully lift the watch glass and dry
it above the flame (otherwise the salt will pop off). *Calculations #1-4 can be
done while you are heating. You must show me the expected mass of salt
before the final massing.
6. Clean up lab station while allowing the dish to cool. Re-mass.
Data:
 mass of empty evaporating dish and watch glass
 mass of reactant (NaHCO3)
 mass of dish, glass, and “dry” product
 re-massing to test dryness
 observations
 error log
Calculations and Questions:
1. Write a balanced equation for the reaction.
2. Predict how much salt should have been produced in the reaction (theoretical yield).
3. Using the balanced equation, determine the theoretical mole ratio of NaCl to NaHCO 3.
4. Calculate the number of moles of NaHCO3 reacted.
5. Calculate the mass of the product, NaCl.
6. Calculate the number of moles of NaCl produced.
7. Calculate the experimental mole ratio of NaCl to NaHCO3.
8. a. Determine the percent error from the mole ratios.
b. Determine another percent error from the predicted mass of salt and the
amount you actually recovered. Calculate your percent yield for the salt.
9. How many carbon dioxide molecules should have been released from the reaction?
10. Baking powder consists of a mixture of NaHCO3 and a substance called
cream of tartar. Baking soda is just pure NaHCO3. Baking powder acts
differently from baking soda. When water is added to baking powder, CO 2
gas is produced. When water is added to baking soda, it just dissolves.
a. What does baking soda require in order to produce carbon dioxide?
b. Why is cream of tartar present in baking powder?
11. What did the splint test show? Why?
Lab Report #5.1:
 Title Page
 Abstract
 Procedure Sheet
 Data
 Calculations and Questions
 Results and Discussion (min. of 3 errors analyzed)
Cary Academy
Chemistry I
W.G. Rushin
2