CLASS 5 · LEARNING KNOWLEDGE

Sieving and filtration as models – basic principles

How it works

Sieving and filtration are methods for separating mixtures of substances. In sieving, solid substances of different particle size are mechanically separated with a sieve: larger particles remain on the sieve, smaller ones fall through. Filtration separates insoluble solid substances from liquids or gases with the help of a filter material. The liquid or gas can flow through the pores, while solid particles remain behind. Dissolved substances are not separated in this process. Both methods are physical separation methods, do not chemically change the substances, and are suitable only for appropriate mixtures, for example for solid mixtures with different particle size or for suspensions.

Note
When sieving or filtering, different particle sizes are used: the sieve or filter material lets smaller particles or the liquid or gas pass through and retains larger, insoluble solid particles. The substances themselves are not chemically changed in the process.

An example

Which separation method is suitable for removing sand from water?

Filtration is suitable, because the sand is retained in the filter as an insoluble solid and the water flows through. A coarse kitchen sieve often does not retain fine sand completely.

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Own explanation and own practice exercises by AmyMath. Subject reference framework: Chemistry. The topic assignment may vary by federal state.