• Question: Why do oil and water not mix?

    Asked by beth5000 to Claire, Matt, Sam on 27 Jun 2013.
    • Photo: Sam Geen

      Sam Geen answered on 27 Jun 2013:

      Water has a surface tension that makes water molecules stick together. The oil can’t break this tension easily. Sometimes things can dissolve because its attracted to water, like the sodium and chlorine in salt being attracted to the weak electric charge of the atoms in water. You can make oil and water mix by adding soap, which has one end attracted to water and one end repelled by it.

    • Photo: Claire Lee

      Claire Lee answered on 27 Jun 2013:

      The water molecule – H2O, is overall neutral, but it has a positive side and a negative side (it’s called being polar). That means that the water molecules get attracted to each other, but they don’t get attracted to oil because oil doesn’t have these charged sides (oil is non-polar).

      Things that dissolve in water are all either polar molecules – so they can be attracted too – or they can break up into charged ions, like sodium and chlorine from salt (NaCl).

      Alcohol is another thing that can help the two mix (like soap).. In fact this can be useful when cooking if you’re making a sauce or something but it’s not mixing together nicely, try adding a bit of alcohol like wine. It’s tastier than soap too (I’ve done that too – but by mistake!)

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