Pupil sheet · Physical and chemical changes
Physical and chemical changes — return questions
Name ______________________ Date ____________
Use one to two weeks after the lessons. Keep the notes and the lesson closed.
1. identify
Four substances are heated, then left to cool. In which row does the result after cooling prove that a new substance was made?
| Row | Before heating | After cooling |
|---|---|---|
| A | purple-black iodine crystals | purple-black crystals on the cool upper part of the tube |
| B | white glucose powder that dissolves in water | a black solid that does not dissolve in water |
| C | white titanium dioxide powder | white powder, after it turned pale yellow while hot |
| D | a grey lump of solder that conducts electricity | a flat strip of solder that still conducts electricity |
Circle one answer.
- A
- B
- C
- D
2. describe
A copper wire is bent into a spring. Hydrogen burns in chlorine to make hydrogen chloride. Describe the difference between these two changes in terms of particles.
(a) Bending the copper wire
(b) Hydrogen burning in chlorine
3. deduce
Ethanol is heated in a water bath until it boils. Bubbles form and rise through the liquid. A pupil says the bubbles prove that a new substance was made. Which reply is best?
Circle one answer.
- The molecules break into atoms, so it is a chemical change
- The bubbles are ethanol vapour, so it is a physical change
- The bubbles are carbon dioxide, so it is a chemical change
- The ethanol stays colourless, so it is a physical change