Separating Solid-Liquid Mixtures PDF

# Separating Solid-Liquid Mixtures 1. **Filtration** can be used to separate an insoluble solid from a liquid. - The insoluble solid is collected as the **residue**. The liquid is collected as the **filtrate**. 2. **Evaporation to dryness** can be used to obtain a soluble solid from a solution...

# Separating Solid-Liquid Mixtures 1. **Filtration** can be used to separate an insoluble solid from a liquid. - The insoluble solid is collected as the **residue**. The liquid is collected as the **filtrate**. 2. **Evaporation to dryness** can be used to obtain a soluble solid from a solution by heating the solution until all the solvent boils off. - the solvent which has a lower boiling point than the solute changes into a gas first. The solute is left behind. - This method is suitable for obtaining solids that do not decompose on heating, e.g. salt. 3. **Crystallisation** can be used to obtain a soluble solid from a solution by allowing a hot saturated solution to cool. - A saturated solution is a solution in which no more solute can be dissolved in the solvent. - This method is suitable for obtaining solids that decompose on heating, e.g. sugar. - Many crystals require a fixed amount of water in its crystal lattice. This water is known as water of crystallisation. If the water is driven off by evaporation to dryness, a powder instead of crystals will be obtained. Thus, crystallisation is used to obtain crystals. 4. The steps of crystallisation are shown below: - **(a) Heat the solution until it is saturated.** - **(b) Leave the hot saturated solution to cool until crystallisation occurs.** - **(c) Filter to collect the crystals. Wash the crystals with cold distilled water and dry them between a few sheets of filter paper.** # Collecting a Gas 2. Some methods of collecting a gas are shown below. | Properties of Gas Collected | Method of Collecting a Gas | |---|---| | insoluble in water, e.g. hydrogen <br> slightly soluble in water, e.g. oxygen, carbon dioxide | displacement of water | | soluble in water, e.g. chlorine <br> very soluble in water, e.g. hydrogen chloride, sulfur dioxide <br> denser than air | downward delivery of gas | | very soluble <br> less dense than air, e.g. ammonia | upward delivery of gas | 3. An inverted measuring cylinder that is filled with water can also be used to measure the volume of a gas through the displacement of water. 4. A gas syringe can be used to collect a gas if the volume of the gas needs to be measured. # Drying a Gas 1. Some methods of drying a gas are shown below: | Drying Agent | Apparatus Set-up | Type of Gas Collected| |---|---|---| | concentrated sulphuric acid | A diagram of apparatus set-up | most gases, including chlorine and hydrogen chloride <br> excluding gases that react with sulphuric acid, e.g. ammonia | | quicklime (calcium oxide) | A diagram of apparatus set-up | ammonia <br> excluding gases that react with quicklime, e.g. hydrogen chloride | | fused calcium chloride | A diagram of apparatus set-up | hydrogen <br> nitrogen <br> carbon dioxide <br> excluding gases that react with calcium chloride, e.g. ammonia |