Separation Techniques - Filtration

Filtration always produces two products: the solid that is trapped, and the liquid that passes through. We need the correct scientific names for each.

The residue is defined as the solid trapped by the filter paper. The filtrate is defined as the liquid that passes through the filter paper and is collected below.

Chalk powder is the insoluble solid trapped on the filter paper — this is the residue. Water passes through and is collected in the flask below — this is the filtrate.

The question asks for the correct scientific names for the solid trapped on the filter paper and the liquid collected below.

The option 'Filtrate on the filter paper; residue collected below' reverses the definitions. The filtrate is the liquid that passes through — it cannot be on top of the filter paper.

'Precipitate' refers to a solid formed during a chemical reaction, not the trapped solid in filtration. 'Distillate' refers to the liquid collected during distillation, not filtration. Both options use incorrect terminology.

The correct answer is residue on the filter paper; filtrate collected below, which matches the standard definitions used in filtration.

Filtration works only when the solid is insoluble in the liquid. If the solid dissolves, its particles become too small to be caught by filter paper.

Sand, chalk powder, and iron filings are all insoluble in water — their particles are large enough to be trapped by filter paper. Salt, however, dissolves in water.

When salt dissolves, its particles break down into individual ions that are far too small to be caught by filter paper. They pass straight through with the water. Therefore, salt dissolved in water cannot be separated by filtration.

The question asks which mixture filtration cannot separate — meaning we are looking for the mixture where the solid is soluble.

'Sand suspended in water' and 'chalk powder mixed with water' both involve insoluble solids. Their particles are large enough to be trapped by filter paper, so filtration can separate them.

'Iron filings mixed with water' — iron does not dissolve in water. Iron filings are insoluble solid particles that would be trapped on filter paper, so filtration can separate this mixture.

Salt dissolves in water, producing a solution where salt ions are too small to be caught by filter paper. Filtration cannot separate this — evaporation would be needed instead.