Filtrate – IGCSE Chemistry Definition

The term “filtrate” is paired with residue — together they describe the two products of filtration. Using the correct term in practical descriptions shows the examiner you understand the technique precisely.

The 0620 definition

The filtrate is the liquid that passes through the filter paper during filtration. It contains dissolved substances but no insoluble particles.

Filtrate in context

Component	Where it goes	Contains
Residue	Stays on filter paper	Insoluble solid
Filtrate	Passes through into flask	Dissolved solute(s) + solvent

Examples in IGCSE Chemistry

Salt preparation from insoluble base

React excess CuO with dilute H₂SO₄, then filter:

• Residue: excess CuO
• Filtrate: CuSO₄ solution (blue) → crystallise to obtain copper(II) sulfate crystals

Preparing insoluble salt by precipitation

Mix Pb(NO₃)₂(aq) with KI(aq), then filter:

• Residue: PbI₂ (yellow precipitate — the product you want)
• Filtrate: KNO₃ solution → usually discarded

Note: in precipitation, the product you want is the residue, not the filtrate. In Method 1 salt preparation, the product you want is the filtrate.

Water purification

Pass turbid water through sand beds:

• Residue: suspended particles, dirt
• Filtrate: clearer water → continues to chlorination

Worked exam question

Excess magnesium is added to dilute hydrochloric acid. The mixture is filtered. (a) Name the filtrate. [1] (b) Describe how to obtain pure, dry crystals from the filtrate. [2]

Mark scheme

(a) Magnesium chloride solution [1]

(b) Heat the filtrate gently to evaporate some water / until the point of crystallisation [1]; allow to cool slowly, filter to collect crystals, and dry [1]

Common exam mistakes

• Confusing filtrate with residue — the filtrate flows through; the residue stays behind.
• Calling the filtrate “pure” — it is a solution containing dissolved substances, not pure solvent.
• Forgetting that the filtrate still needs processing (crystallisation) before you have solid salt crystals.