Question: how can we separate a mixture of sand and iron filings?

Priscilla Ngotho answered on 23 Sep 2014:

@ 225heaa23 To separate any mixture you have to consider the physical and chemical properties of the individual components of the mixture. If there is a unique property in one of the components then it can be exploited to separate it from the mixture. In this case iron is a metal which has magnetic property. The Iron filings will be attracted by a magnet. So what you need to do is get a strong magnet and pass it through the mixture. All the iron filings will be removed by the magnet and you will be left with only sand.

Note that some mixtures are much more complex and difficult to separate. For example biological samples like blood. To separate blood components we exploit their differences in physical state (solid vs liquid) and densities. Plasma is liquid while the red and white cells are solid particles. Therefore we use sedimentation. The cells separate from each other based on density. The red cells are most dense and settle at the bottom. White cells are less dense and settle on top of red cells and the liquid plasma is the topmost layer.

Think of other complex mixtures and list down the different properties of each constituent and you will find the best method of separation.