You are here
Question
You are given a mixture of sand, common salt and naphthalene (Fig. 5.25a). The Fig. 5.25b depicts various steps used to separate the components of this mixture. Identify and write down the correct sequence of separation techniques.
Show answer
Answer
The correct order is
1, then 3, then 2
.
The scientific order
- First sublimation — heat the mixture and the naphthalene sublimes away, leaving sand and salt.
- Then add water and filter — the salt dissolves and the sand is held back on the paper as the residue.
- Finally evaporate or crystallise the filtrate to recover the salt.
⚠️ Why the order cannot change
- Sublimation must be done first. Once water has been added, separating the naphthalene becomes very difficult.
Which picture is which
| Picture | What it shows | Step |
|---|---|---|
| Picture 1 | A china dish on a burner with an inverted funnel over it, its tube plugged with cotton and white solid depositing on the inner wall | Sublimation — the Activity 5.7 set-up |
| Picture 2 | A china dish on a burner holding clear liquid, with no funnel above it | Evaporation — drying the filtrate to get the salt |
| Picture 3 | A funnel with filter paper on a stand, a hand pouring in the mixture, clear liquid dripping into a beaker below | Filtration |
Notice that the pictures are not printed in working order — that is precisely what makes this a question.
Picture 1 gives the naphthalene, picture 3 gives the sand, picture 2 gives the salt.
← Back to: 5.4.2 Sublimation
