Reactions that give off carbon dioxide are used to raise dough when baking bread. On cooking, the bubbles of carbon dioxide become trapped in the dough and give the bread a pleasing texture. The ingredients are made into a dough which is left in a warm place for about 30 minutes. The volume of the dough increases as carbon dioxide is produced from the sugar by the yeast.<br>Recipe card, NAAN INDIAN BREAD, ingredients<br>$$75\ \text{cm}^3$$ of milk<br>1 teaspoon of sugar<br>1 teaspoon of yeast<br>200 g of plain flour<br>$$\frac{1}{2}$$ teaspoon of baking powder (sodium hydrogencarbonate and tartaric acid)<br>1 tablespoon of vegetable oil<br>$$75\ \text{cm}^3$$ of plain yogurt<br>1 egg<br>$$\frac{1}{4}$$ teaspoon of salt<br>a) There are two ionic compounds in the recipe. Name one of them.<br>The dough is then placed in a hot oven and the baking powder produces more carbon dioxide as the naan bread cooks. Sodium hydrogen carbonate decomposes when heated.<br>$$\mathrm{2NaHCO_3 \rightarrow Na_2CO_3 + CO_2 + H_2O}$$<br>Sodium carbonate has an unpleasant taste. It reacts with the tartaric acid to form sodium tartrate which has a pleasant flavour.<br>b) What type of compound is sodium tartrate?<br>c) Suggest two reasons why baking powder is a mixture of tartaric acid and sodium hydrogen carbonate, and not just sodium hydrogen carbonate.