Separating Mixtures: Filtration, Evaporation, Distillation and More — Answers
Answer sheet with model answers and success criteria for the 7th Grade mixtures & chemical reactions worksheet.
Success TutoringWorksheetsAnswer sheet7th Grade · Science · Mixtures & Chemical ReactionsSeparating Mixtures: Filtration, Evaporation, Distillation and More — Answers
Part A: Choose the method
Circle the best method for each separation.
A mixture contains two or more substances that are mixed together but not chemically joined. Because each substance keeps its own properties, we can separate them by physical methods that use a difference in those properties.
Filtration separates an insoluble solid from a liquid. The liquid that passes through the filter paper is the filtrate; the solid left on the paper is the residue.
Evaporation recovers a dissolved solid (the solute) from a solution by letting the liquid (the solvent) turn into a gas and escape. The solvent is not collected.
Distillation separates a liquid from a solution, or two liquids with different boiling points. The liquid is boiled, the vapor is cooled in a condenser, and the liquid collected is the distillate.
Magnetic separation pulls magnetic materials (such as iron, steel, nickel and cobalt) away from non-magnetic ones. Sieving separates solids with different particle sizes.
Paper chromatography separates dissolved substances, such as the dyes in an ink. A spot of ink is placed on a pencil line near the bottom of the paper, and a solvent soaks up the paper. Substances that are more soluble in the solvent travel further.
Safety: evaporation and distillation involve heating, so they are done in the school laboratory with your teacher.
- Afiltration
- Bevaporation
- Cdistillation
- Dmagnetic separation
- Echromatography
- Fsieving
Answer: filtration
Sand is insoluble in water. Filter paper lets the water through but traps the sand grains.
- Afiltration
- Bevaporation
- Cdistillation
- Dmagnetic separation
- Echromatography
- Fsieving
Answer: evaporation
Salt is dissolved in the water. Evaporating the water (the solvent) leaves the salt (the solute) behind as crystals.
- Afiltration
- Bevaporation
- Cdistillation
- Dmagnetic separation
- Echromatography
- Fsieving
Answer: distillation
Distillation boils off the water and then cools the vapor in a condenser, so the pure water is collected. Evaporation alone would lose the water to the air.
- Afiltration
- Bevaporation
- Cdistillation
- Dmagnetic separation
- Echromatography
- Fsieving
Answer: magnetic separation
Iron is magnetic and sulfur is not, so a magnet pulls out the iron.
- Afiltration
- Bevaporation
- Cdistillation
- Dmagnetic separation
- Echromatography
- Fsieving
Answer: chromatography
In chromatography, different dyes travel different distances up the paper, so the separate dyes show up as separate spots.
- Afiltration
- Bevaporation
- Cdistillation
- Dmagnetic separation
- Echromatography
- Fsieving
Answer: sieving
The particles are very different sizes. The fine flour falls through the holes of a sieve and the peas stay on top.
Part B: True or false?
Write T for true or F for false.
Answer: True
Air is a mixture of gases, mainly nitrogen and oxygen, with smaller amounts of argon, carbon dioxide and water vapor. They are not chemically joined.
Answer: False
In a mixture the substances are only mixed. If they were chemically bonded, they would form a compound, which needs a chemical reaction to separate.
Answer: True
The filtrate passes through; the residue stays on the paper.
Answer: False
The water vapor escapes into the air. To collect the water as well, you need distillation.
Answer: False
Pen ink can dissolve in the solvent and separate too, which would spoil the results. Pencil (graphite) does not dissolve, so the line stays put.
Answer: True
If the spots were below the solvent level, the ink would dissolve into the solvent in the container instead of traveling up the paper.
Part C: Key words
Fill each gap with the correct science word.
Answer: condenser
Answer: soluble; insoluble
Answer: solute; solvent
Answer: residue
Part D: Apply it
Answer in full sentences.
Answer: 1. Use a magnet to remove the iron filings (do this while the mixture is dry). 2. Add water and stir so the salt dissolves; the sand does not dissolve. 3. Filter the mixture: the sand is left on the filter paper as the residue and the salt solution passes through as the filtrate. 4. Evaporate the water from the filtrate to leave salt crystals. 5. Rinse the sand with a little clean water and let it dry.
Answer: Water boils at 100 °C (at normal air pressure), while salt has a very much higher boiling point (well over 1000 °C). When the solution is heated, the water boils off as vapor and the salt stays behind. The vapor is then cooled in the condenser and collected as pure water.
Answer: Ink X contains dyes A and C. Each dye travels the same distance up the paper under the same conditions, so spots at matching heights show the same dye. No spot in X matched dye B, so B is not in the ink.
Part E: Explain
Model answer: Filtration removes the insoluble particles such as mud and sand, so the water looks clearer, but dissolved salts pass straight through the filter paper with the water because their particles are spread through the solution. To get pure water, the filtered water could be distilled: the water boils and is condensed and collected, while the dissolved salts are left behind because they have much higher boiling points.
Success criteria:
- States that filtration removes insoluble solids only
- Explains that dissolved substances pass through the filter with the water
- Names distillation (after filtering) as the method that gives pure water
- Explains distillation using boiling and condensing
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.
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