Page 14 - Curriculum Visions Dynamic Book

Using carbon dioxide
Carbon dioxide is sometimes used in its solid form – as dry ice – to create the impression
of fog. It is safe, clean and easy to control in theatres because of three important properties: carbon dioxide sublimes (changes straight from
a solid to a gas and vice versa), is heavier than air and is noncombustible.
Carbon dioxide gas is produced during the preparation of both food and drink, in some cases for effect (as in carbonated water), in other cases to “lighten” dough, cakes and pastries.
Baking
The lightness of many baked flour-based foods depends on the dough, pastry, etc., containing a large number of bubbles of carbon dioxide gas. This can be achieved by heating baking soda (sodium bicarbonate), causing it to decompose, and thus releasing carbon dioxide gas.
Baking powder is a mixture of baking soda (sodium bicarbonate), tartaric acid, and small amounts of starch. As soon as the acid and the baking soda
are wetted they begin to react, releasing
carbon dioxide. The amount and size of the bubbles depend on the rate at which the gas bubbles are created, larger bubbles being released by greater amounts of gas.
Carbon dioxide gas is usually used to lighten the texture of (or leaven) doughs, sweet pastries and cakes.
 This cake shows how carbon dioxide bubbles form from the reaction of baking powder. The bubbles become trapped
by the stickiness of the dough, thus giving cakes their light texture.
 Fizzy drinks contain carbonated water, that is, water in which carbon dioxide has been dissolved under pressure. In some cases the carbon dioxide is formed in the bottle or can by mixing an acid (such as phosphoric acid) and an alkali with the drink just before it is sealed in its container. These react to produce gas, although the gas remains dissolved while the container is closed.
When the cap is loosened, the pressure is reduced and the carbon dioxide comes out of solution, producing bubbles: the fizz.
Dry ice
Frozen carbon dioxide is called dry ice and is used for portable refrigeration and to create swirling fog on theatre stages or movie sets.
EQUATION: Producing carbon dioxide by heating baking soda
Sodium bicarbonate ➪ sodium carbonate + carbon dioxide + water 2NaHCO3(s) ➪ Na2CO3(s) + CO2(g) + H2O(l)
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