CHE L110 - Chemistry and Society Laboratory
Experiment #4
Table Salt from Baking Soda

INTRODUCTION

When a chemical reaction takes place, the amount of product that can be produced is determined by the amounts of each reactant used, the molar mass of reactants and products, and the balanced chemical equation.

In this experiment you are going to prepare table salt (NaCl, sodium chloride) from baking soda (NaHCO₃, sodium bicarbonate or sodium hydrogen carbonate).

You might recognize this reaction as the same one that you used to prepare carbon dioxide gas in Experiment #2. The balanced chemical equation tells you that for every one NaHCO₃ that reacts, one NaCl is produced.

The molar mass (MM) of a compound is equal to the sum of the atomic weights of all of the atoms in the compound. Atomic weights are found below the element symbol on the periodic table.

       For NaHCO₃: molar mass (MM) = (22.99) + (1.08) + (12.01) + (3 x 16.00) = 84.08

       For NaCl: molar mass (MM) = (22.99) + (35.45) = 58.44

You are going to perform a quantitative experiment to determine the mass of NaCl that can be produced from a specific amount of NaHCO₃. In addition, you will calculate the theoretical amount of NaCl that can be produced and compare the two. The theoretical amount of NaCl that can be produced from a weighed amount of NaHCO₃ and excess HCl is given by:

USE OF LABORATORY BALANCE

This experiment requires careful weighing in order to obtain good results. A page of instructions on the proper use of the laboratory balance is attached at the end of the Experimental Procedure. All masses should be reported to TWO decimal places (e.g. 7.32 g or 16.40 g).

EXPERIMENTAL PROCEDURE

1. Obtain three large test tubes that are clean and completely dry. With a marker pen, label the test tubes A, B, and C. Put the label near the top of each test tube.

2. Lay each empty test tube flat on the balance pan. Weigh each test tube to the nearest hundredth of a gram (0.01 g). Record the mass of each test tube on the report sheet data table.

3. Using a scoop or spatula, add just enough NaHCO₃ (sodium bicarbonate) to each test tube to fill the curved bottom of the tube.

4. Reweigh each test tube to the nearest hundredth of a gram (0.01 g). Record the mass (test tube + NaHCO₃) on the report sheet data table. The mass of NaHCO₃ does not have to be the same in each test tube. The mass of NaHCO₃ should be between 0.3 and 0.7 g.

5. Using a plastic pipet, add 10% hydrochloric acid (HCl) solution dropwise to test tube A. Allow the HCl solution to run down the inside wall of the test tube. Gently agitate the test tube after each drop reaches the bottom. Add HCl slowly until all of the solid has dissolved. Observe what happens. Continue to add HCl dropwise (agitating the test tube after each drop) until no more gas bubbles (CO₂) are observed. It is important to add only the minimum amount of HCl to completely dissolve the solid and release all of the gas. Save the test tube and its contents for further work.

6. Repeat step 5 with each of the other test tubes (B and C).

7. GENTLY heat test tube A and its contents in a Bunsen burner flame, holding the test tube at an angle and pointed away from you and anyone else in the lab. You want to evaporate ALL of the water in the test tube without spattering anything out of the test tube.

CAUTION: Too rapid heating of the test tube, especially if it is held in an upright position , will cause the hot contents to splash out of the tube. If this happens, you will have to start over with a new sample.

Continue heating the test tube until ALL of the liquid has evaporated and only solid NaCl remains. It is critical for the success of this experiment to be sure that all of the water has evaporated from the upper part of the test tube.

8. To test that all of the water has been evaporated, remove the test tube from the flame and hold an inverted, clean dry test tube over the upright mouth of test tube A. If condensation appears in the cold test tube, continue the drying and testing process until no condensation occurs. Then stand test tube A up in your large beaker to cool.

9. Repeat steps 7 and 8 with test tubes B and C.

10. Allow each test tube to cool for at least 5 minutes. You do not want to weigh a hot test tube. Reweigh each test tube to the nearest hundredth of a gram (0.01 g). Record the mass (test tube + NaCl) on the report sheet data table.

11. After you have completed the experiment, rinse each test tube with tap water and pour the contents down the drain. Make sure each test tube is clean and dry before you put it away.