Experimental design — practice question

Baking soda helps bread rise. When baking soda is heated, it breaks down and carbon dioxide gas is given off. Baking soda also breaks down slowly while it is stored. The longer it is stored, the less carbon dioxide it gives off when heated. Plan an investigation to show which of two different samples of baking soda has been stored for longer. Your plan should include the use of common laboratory apparatus and the two samples of baking soda. No other chemicals are to be used. Your plan should include: - the apparatus needed - the method to use - the measurements to take - the variables to control - how to use the results to decide which sample has been stored for longer. You may draw a diagram to help you answer the question.