Shake a spatula measure of powdered chalk with 30 cm3 of distilled water in a boiling tube. A cloudy white mixture is formed. Chalk does not dissolve in wat...

This tests filtration, used to separate an insoluble solid from a liquid. Chalk (calcium carbonate) does not dissolve, so its particles are trapped by the filter paper as the residue while the water passes through as the filtrate. The figure shows the paper folded twice into a cone ready for the funnel.

(a) [2] To fit the cone: open the folded paper so there are three thicknesses on one side and one on the other [1], then sit it in the funnel and wet it with a little distilled water so it lies flat against the glass [1]. Wetting seals the paper to the funnel so mixture cannot run down the gap between paper and glass.

(b) [1] The mixture is poured down a glass rod so it does not splash over the top edge of the filter paper, and to control the flow into the cone [1]. If it splashed over the rim, unfiltered mixture would carry chalk into the filtrate.

(c) [1] When it has all drained, the filtrate is a colourless, clear liquid [1], because the solid chalk has been held back on the paper.

(d) [2] To show all the chalk has been removed, give any two of: hold a portion up to the light and look for cloudiness [1]; a clear, non-cloudy filtrate shows no solid remains [1]; or stand a portion in a boiling tube and check that no solid settles out on standing [1]. Any lingering cloudiness or sediment would mean fine chalk had passed through.