Dissolving: Soluble and Insoluble Substances — Answers
Answer sheet with model answers and success criteria for the Year 6 mixtures & chemical reactions worksheet.
Success TutoringWorksheetsAnswer sheetYear 6 · Science · Mixtures & Chemical ReactionsDissolving: Soluble and Insoluble Substances — Answers
Part A: What happens when things dissolve?
Read the passage. Then circle the best answer.
When you stir sugar into water, the sugar seems to disappear. It has dissolved — it has broken into tiny pieces too small to see and spread evenly through the water.
The substance that dissolves is the solute (sugar). The liquid it dissolves in is the solvent (water). Together they make a solution (sugar water).
Substances that dissolve are soluble, such as salt, sugar and instant coffee. Substances that do not dissolve are insoluble, such as sand, chalk and flour — they make the water cloudy or sink to the bottom.
A dissolved substance has not gone. The solution weighs the same as the water and solute added together, and if the water evaporates, the solute is left behind.
Things dissolve faster when the water is warmer, when you stir, and when the solute is in smaller pieces.
- Asand
- Bsalt
- Cchalk
- Dpebbles
Answer: salt
Salt dissolves in water — it breaks into pieces too small to see and spreads through the water.
- Asolvent
- Bsolute
- Csolid
- Dfilter
Answer: solvent
The solvent is the liquid that does the dissolving. The sugar is the solute.
- Ausing colder water
- Busing a bigger sugar lump
- Cstirring the water
- Dnot touching the cup
Answer: stirring the water
Stirring moves fresh water past the sugar, so it dissolves faster. Warm water and smaller grains also help.
- A200 g
- B150 g
- C50 g
- D250 g
Answer: 250 g
The salt is still there, just spread out, so nothing is lost: 200 g + 50 g = 250 g.
- ALet the water evaporate.
- BUse a sieve.
- CAdd more water.
- DPut it in the freezer for an hour.
Answer: Let the water evaporate.
When the water evaporates, the salt is left behind as crystals. A sieve or filter cannot catch dissolved salt.
Part B: Words and separating
- solute
- solvent
- solution
- the mixture made when something dissolves
- the substance that dissolves
- the liquid that does the dissolving
Answer: solute → the substance that dissolves; solvent → the liquid that does the dissolving; solution → the mixture made when something dissolves
Answer: insoluble
Answer: Pour the mixture through a filter (such as filter paper or a coffee filter). The water passes through and the sand is caught.
Part C: True or false?
Write True or False.
Answer: False
The salt is still in the water, spread out in tiny pieces. Evaporating the water brings it back.
Answer: True
Smaller grains have more surface touching the water, so they dissolve faster.
Answer: False
Flour does not dissolve. It makes the water cloudy and settles to the bottom.
Answer: True
Once no more will dissolve, the extra sugar sits at the bottom. The solution is then called saturated.
Part D: Working scientifically: sugar cubes and temperature
Use Zoe's results to answer. Ask an adult to help with warm water.
Zoe put one sugar cube into each of three cups holding 100 mL of water at different temperatures. She timed how long each cube took to dissolve completely, without stirring.
20 °C: 120 seconds · 40 °C: 60 seconds · 60 °C: 25 seconds
Answer: The temperature of the water.
Answer: The 60 °C cup (25 seconds).
Model answer: The warmer the water, the faster the sugar cube dissolved: 120 seconds at 20 °C, 60 seconds at 40 °C and 25 seconds at 60 °C. To keep it fair, Zoe used the same amount of water and the same size sugar cube each time and did not stir any of the cups.
Success criteria:
- States the pattern: warmer water, faster dissolving
- Uses the data
- Names a controlled variable
Marking tips
- Give credit for correct method even when the final answer slips — the working shows where the thinking went right.
- For open-ended tasks, use the success criteria as a checklist rather than looking for one "right" answer.
- Celebrate what went well first, then pick one thing to work on next.