Question 1: Explain what happens to the starch content in a potato when it is cooked and how this is a chemical change.

Answer: When a potato is cooked, heat causes the starch granules to swell and gelatinise, resulting in a change in texture and appearance. This is a chemical change because new substances may form, and the structure of the starch is altered permanently.

Question 2: Describe what occurs during the caramelisation of sugar and why it is considered a chemical change.

Answer: Caramelisation involves heating sugar until it melts and turns brown, creating new flavours and a different colour. It is a chemical change because it produces new substances with different properties from the original sugar.

Question 3: Identify two signs that a chemical change has taken place when cooking an egg.

Answer: Signs include the egg white turning opaque and solidifying, and the yolk changing colour and becoming firmer.

Question 4: Describe what happens to the protein in meat during cooking and whether this is a physical or chemical change.

Answer: The proteins in meat denature and coagulate, causing the meat to firm up and change texture. This is a chemical change because new protein structures are formed that cannot be reversed.

Question 5: Draw a diagram of a simple food item undergoing a chemical change, such as bread baking. Label the key changes happening inside the food.

Answer: A sketch should show bread dough with yeast, heat, and the formation of bubbles and crust. Labels should include 'yeast fermentation', 'carbon dioxide production', 'starch gelatinisation', and 'crust formation'.

Question 6: Explain why the browning of apples when cut and left exposed to air is considered a chemical change.

Answer: The browning is caused by oxidation of phenolic compounds in the apple, forming brown pigments. This process is a chemical change because new substances are created, and it cannot be reversed by simple physical means.

Question 7: Identify the type of chemical change involved when milk sours and explain what causes it.

Answer: Milk sours through fermentation, where bacteria convert lactose into lactic acid. This is a chemical change because new substances (lactic acid) are formed, altering the milk's properties.

Question 8: Describe how the process of baking a cake involves chemical changes, and mention at least two specific changes that occur.

Answer: Baking a cake involves chemical changes such as the Maillard reaction, which browns the surface, and the coagulation of proteins and gelatinisation of starches, which helps form the cake's structure. These changes are irreversible and produce new substances.

Question 9: Sketch a flowchart illustrating the sequence of chemical changes in the process of making toffee from sugar.

Answer: The flowchart should include: heating sugar -> melting and caramelisation -> formation of caramel colour and flavour -> cooling and solidifying into toffee. Labels should highlight key chemical transformations like caramelisation.