Chemistry of cake baking

A delicious fluffy cake just doesn't happen by chance. It takes a harmless chemical reaction to make a cake fluffy and light. Baking powder is mixed with an acid to produce carbon dioxide. This gas
is harmless when eaten. As it becomes hot in the oven the gas expands and makes bubbles in the cake mixture. This makes the cake rise.

A cake is made fluffy by the production of carbon dioxide. Click to see a movie of carbon dioxide production using vinegar and baking powder.
Explain how carbon dioxide trapped under the dough causes the cake to rise when heated.
When a carbonate (Bicarb Soda) is mixed with an acid, such as vinegar, carbon dioxide gas is produced. You will find that many recipes have, as ingredients, baking powder and some kind of acid, usually it is tartaric acid.
1) Have a look at the movie clip on carbon dioxide and fire, shown on the right. One of the properties of carbon dioxide gas is that it is heavier than air. This means it will sink to the bottom of the container it is kept in. What is the other property of carbon dioxide gas?
2) Cooks put ascorbic acid and bicarb soda into bread and cake mixtures. Suggest why?

3) Some confectionery fizzes in your mouth. They contain
bicarb soda and citric acid. Explain how the fizz sensation is created.

4) Some chefs use yeast. Explain why yeast is used in cake baking?

5) Where else is yeast used?