How do you separate a mixture containing one water-soluble and one water-insoluble substance?

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joyclarke's profile pic

joyclarke | (Level 1) Adjunct Educator

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To separate a water soluble substance (e.g. NaCl) from a water insoluble substance (e.g. sand), we can use the properties of water as a solvent, and the fact that filter paper has pores which allow molecules up to a certain size to pass through while preventing larger molecules from doing so.

We can follow the steps below:

Place about 2 grams of each of the soluble and insoluble substances in the same 250 ml beaker.

Pour about 200ml of water into the beaker and stir to dissolve the salt.

Set up a conical flask with a filter paper and pour the mixture to allow it to filter.

To recover the salt:

Pour the filtrate (in the flask) into a beaker and heat slowly over a low Bunsen flame until most of the water has evaporated, then leave it for the rest to evaporate at room temperature.

To recover the sand:

Pour some water over the residue (in the filter paper) to remove any remaining salt and allow to dry at room temperature.

gsenviro's profile pic

gsenviro | College Teacher | (Level 1) Educator Emeritus

Posted on

To separate out a mixture of one water-soluble and one water-insoluble substance, we can use filtration and evaporation. The water-insoluble substance can be separated out by filtration (using a filter paper or membrane, depending on the size of the substance). The water-soluble substance can be obtained by evaporating the water (in a laboratory oven or over water bath).

The steps to achieve this can be summarized as:

  • Filter the mixture through a filter paper and collect the filtered water in another container.
  • Dry the filter in an oven or a desiccator and collect the water-insoluble substance from it. If you need the quantity of water-insoluble substance, it can be estimated by the change in the weight of the filter paper, before filtration and after drying it.
  • The filtered water can be boiled to evaporate all the water. The residue after drying in an oven or desiccator (preferably) will be the water-soluble substance.

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