Year 7 Science · Unit 2 · Lesson 7
Foundation Worksheet
Learning Goals
Fill the gap
Choose the correct word from the word bank. Each word is used at most once. Two words are not needed: cross them out.
Distillation separates a mixture using differences in point. The part with the boiling point turns into a vapour first, then the cools it back into a liquid. separates dissolved substances by how far a liquid called the carries them up a paper strip. Spot distance ÷ solvent distance gives each spot’s value.
Match each part to its job
Write the letter of the correct job next to each part of a distillation set-up. Each letter is used once.
| Part | Letter | Its job |
|---|---|---|
| Flask A | A. Collects the liquid that drips out of the condenser. | |
| Heat source | B. Holds the mixture that is being separated. | |
| Thermometer | C. Cools the vapour so that it turns back into a liquid. | |
| Condenser | D. Shows the temperature of the vapour leaving the flask. | |
| Flask B | E. Warms the mixture until one part of it boils. |
Sort it
For each job, ask: “Do I want to keep the solid, collect the liquid, or only find out what is in the mixture?” Then write the job in the correct box. The boxes do not hold the same number of items.
Evaporation (keep the solid)
Distillation (collect the liquid)
Chromatography (find out what is there)
1. Some nail-polish removers are a mixture of acetone (boiling point 56 °C) and water (boiling point 100 °C). The mixture is heated in Flask A of a distillation set-up. Which liquid collects in Flask B first? Explain why.
Read the data
Scenario: what is in a purple marker?
Chloe puts a spot of ink from a purple marker on the start line of a paper strip and stands the strip in water. When she takes it out, the water has moved 10.0 cm up the paper. The ink has split into three coloured spots.
| Spot colour | Distance the spot moved (cm) | Rf value |
|---|---|---|
| Blue | 7.5 | 0.75 |
| Pink | 5.0 | 0.50 |
| Red | 3.0 |
Source: made-up class results for this worksheet.
2. Work out the Rf value of the red dye. Show your working, then write the answer in the empty box in Table 1.
Rf = (no unit)
3. (a) How many different dyes are in the purple ink? (b) Which dye is the most soluble in water? Use Table 1 to explain how you know.
4. Jai is camping by the sea and needs drinking water. He says: “I’ll boil sea water in an open pot until it’s all gone. That is the same as distillation, because both use boiling point.” Explain whether Jai is right, and what he should do instead.
Fill the gap
boiling; lower; condenser; Chromatography; solvent; Rf. Not needed: higher, filtration.
Match each part to its job
Flask A → B; Heat source → E; Thermometer → D; Condenser → C; Flask B → A.
Sort it
Evaporation: salt from sea water, in a salt pan; sugar crystals from sugary water. Distillation: drinking water from sea water, on a ship; an ethanol-enriched distillate from an ethanol-water mixture; pure water from salty water, in the lab. Chromatography: do two blue pens hold the same ink?; is there a banned dye in this cordial?; which drug is in a tiny blood sample?.
Question 1
Acetone collects first (1). It has the lower boiling point, so it turns to vapour first, then the condenser cools it back to liquid and it drips into Flask B (1). [2 marks]
Read the data
2. Rf = distance moved by the spot ÷ distance moved by the solvent = 3.0 ÷ 10.0 (1) = 0.30, with no unit (1). [2 marks]
3. (a) Three dyes: one for each spot (1). (b) The blue dye (1): it has the highest Rf value (0.75), so it travelled furthest, and the more soluble a dye is, the further the solvent carries it (1). [3 marks]
Question 4
Marking guide: 1 Jai is wrong; 1 an open pot is evaporation: the steam escapes into the air; 1 so he is left with salt and no water to drink; 1 distillation catches the steam in a condenser, which cools it back into liquid water; 1 pure water collects in Flask B and the salt stays in Flask A, so he should distil (or at least catch and cool the steam). [5 marks]
Model answer: Jai is wrong. Boiling sea water in an open pot is evaporation: the steam escapes into the air, so he ends up with a crust of salt and nothing to drink. Distillation uses the same property, boiling point, but a condenser catches the steam and cools it back into liquid, so pure water drips into Flask B while the salt stays in Flask A. Jai needs to distil the sea water, because the water is the part he wants to keep.
Common error: treating evaporation and distillation as the same. Both boil the water off; only distillation keeps it.