Isopropyl alcohol is frequently purchased as a mixture with water. These two liquids are miscible, meaning that they mix together completely, essentially dissolving in each other. It is not normally possible to remove the isopropyl from the water to concentrate it. However, you can use an interesting procedure known as "salting out" to separate the two liquids. In this technique, salt is added to the water, disrupting its ability to mix with the alcohol. Educators may find the separation of isopropyl alcohol and water is a good demonstration of this principal for their students.
- Skill level:
- Moderately Easy
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Things you need
- Dilute isopropanol (mixed with water)
- Table salt
- Stir stick
Fill a beaker approximately three quarters full with the isopropyl alcohol/water mixture. The beaker appears to contain only one liquid, with the alcohol and the water completely mixed.
Add approximately 10 grams of table salt (NaCl or sodium chloride) to the mixture in the beaker and stir to dissolve the salt. As the salt dissolves, see the alcohol begin to separate and form a distinct layer of its own on top of the water. Both the alcohol and the water layers are clear and colourless, but there is a distinct horizontal boundary between the two, part way down the beaker. Wait a few minutes to allow the two layers to fully separate.
Add a further 10 grams of salt and stir to dissolve. Again wait to let the mixture come to equilibrium. If the volume of the upper alcohol layer does not appear to have increased from the previous addition of salt, you have obtained the maximum separation possible by salting out. If the layer appears larger, continue to add salt until you do not see any further change.
Carefully pour off the upper layer from the beaker. This layer is concentrated isopropyl alcohol, containing only a trace of water.
Tips and warnings
- This procedure works best when the percentage of isopropyl alcohol in the mixture is relatively high; approximately 50 per cent or greater.
- Isopropyl alcohol is also known as propanol or 2-propanol.
- Isopropyl alcohol can be hazardous to your health. Read the material safety data sheet for this chemical before working with it.
- You should only perform this procedure if you have the training and education to safely work with chemicals.
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