Separation techniquesIB MYP Chemistry: Flashcards

Exam questions on Separation techniques

1. A school laboratory technician has four mixtures to separate. Mixture W is sand and water. Mixture X is salt dissolved in water, and she wants to collect the salt. Mixture Y is seawater, and she wants to collect pure water. Mixture Z is a liquid mixture of ethanol, which boils at 78 °C, and water, which boils at 100 °C, and she wants to collect both liquids.
   Explain why filtration cannot be used to collect the salt from mixture X.2 marks
2. A student wants to obtain pure crystals of copper sulfate from a blue copper sulfate solution. She heats the solution in an evaporating basin until about half of the water has gone. Every so often she dips a clean glass rod in the hot solution and lets the drop cool, until small crystals form on the rod. She then stops heating, leaves the solution to cool, separates the crystals from the liquid and dries them between filter paper.
   Explain why the solution is left to cool before the crystals are separated, and why they are then dried.2 marks
3. A student is given 10.0 g of a mixture of sand, salt and iron filings and must separate and recover all three substances. After she has dried each one, the masses she recovers are: iron 1.0 g, sand 3.6 g and salt 4.9 g.
   Outline a method that she could use to separate sand, salt and iron filings from the mixture.3 marks