The Decomposition of Baking Soda

Experiment 9 – Decomposition of Baking Soda

Introduction

The decomposition of any metal hydrogen carbonate will result in the formation of that metal carbonate, water vapor, and carbon dioxide. This lab will investigate the decomposition of sodium hydrogen carbonate, NaHCO3, commonly called baking soda. It is governed by the following chemical equation:

2 NaHCO3sNa2CO3s+ H2O g+ CO2 (g)

In this lab, the NaHCO3 will be decomposed to form Na2CO3. The first half of the experiment will use a pure sample of NaHCO3, and the second part will use a mixture containing only some NaHCO3. Depending on how well the first half of the experiment is performed, the percent yield of this reaction should be 100%. The second half of the experiment should see something less than 100%, since it is not a pure sample.

Percent yield is defined as the actual yield divided by the theoretical yield. The actual yield is the amount of product one produces during the experiment. The theoretical yield is the amount of product one should have produced.

% Yield= actual yieldtheoretical yield x 100%

Unless there are experimental errors, the % Yield should not be over 100%. In many cases, especially ones in which the reaction is difficult to control; the % Yield can be much lower than 100%.

In the case of impure samples, like in the second half of this lab, the % Yield can give the percent of active material in the sample. The concept is the same. The only trick is to keep track of which value is the actual amount, and which is the theoretical amount.

Refer to the sample calculations for more insight.

Equipment

100 or 250 mL beaker
Watchglass
Bunsen burner
Wire gauze
Iron ring
NaHCO3
Unknown sample

Examples

Percent Yield from a Pure Sample

A 0.685 g sample of Ca(HCO3)2 is decomposed by heating to form CaCO3. When the sample is cooled it