Chapter 8 – Changes of materials
Consider the following statements and click to reveal the answer.
1. What happens when you add tea leaves to water?
Some of the chemicals from the tea leaves dissolve in the water, but the leaves themselves do not dissolve.
2. Where does the oxygen come from in this chemical reaction?
iron + oxygen = iron oxide
It comes from the air. Air is a mixture of gases, including oxygen.
3. How is the process of burning similar to what happens when living things respire?
The overall chemical reaction is identical.
4. Where does the oxygen come from when a material is burnt?
It usually comes from the air. Air is a mixture of gases, including oxygen.
5. What happens when table salt dissolves in water?
When salt is added to water, the slight negative charges in the water are able to attract the sodium chloride ions and pull them off the salt crystals, thus dissolving the salt.
6. What would happen to the cap of a full bottle of water that is kept in the freezer? Explain your answer.
The cap would be forced off the bottle. When water freezes it expands. This means that the same amount of water will occupy a bigger volume as a solid (ice) than as a liquid (water). If the bottle was full of liquid water, then the frozen water would need more space and so the cap would be pushed off to make the extra space.