Physical and chemical changesIB MYP Chemistry: Flashcards

Exam questions on Physical and chemical changes

1. Students in Nairobi observe four changes in a kitchen. Butter melts in a warm pan. Sugar dissolves in hot tea. Bread turns brown and crisp in a toaster. A cake mixture rises, turns golden brown and gives off a new smell in the oven.
   Give two pieces of evidence from the description that baking the cake involves a chemical change.2 marks
2. A student in Cairo adds a 3 cm strip of magnesium ribbon to dilute hydrochloric acid in a test tube. The ribbon fizzes and gradually disappears, and the temperature of the mixture rises from 21 °C to 33 °C.
   Explain why the changes in the test tube are chemical rather than physical.2 marks
3. Students in Manila heat 2.00 g of blue crystals of hydrated copper(II) sulfate in a test tube. The crystals turn white, droplets of liquid form on the cooler upper part of the tube, and the mass of solid left is 1.28 g. After the tube has cooled, the students add a few drops of water to the white powder. It turns blue again and the tube feels warm.
   Describe three pieces of evidence from the investigation that show chemical changes took place.3 marks