Turn your salad dressing into a science experiment and learn about the unmixables: water and oil...
Science: oil, vinegar, glass, optional: honey, washing-up liquid, food colour, dropper
Supper: oil, vinegar, salt and pepper, jar with lid, tomato, cucumber, optional: honey, dijon mustard, cheese
1. Prepare supper
Measure 2 tbsp oil and 1 tbsp vinegar into a jar
Notice that they settle into two layers; which is on top?
Pop the lid on and shake – what happens?
Leave it a few minutes and they will seperate again
Add a pinch of salt and pepper
Add 1 tsp each of honey and mustard, if liked, and shake again
Chop up the tomato and cucumber or any other salad veggies you like, grate or crumble in some cheese, drizzle over the salad dressing and serve
2. Do some science
Put some oil into a small glass
In another glass, add food colouring to water
See what happens when you add drops of coloured water into the oil
It works best with a dropper but you can use a spoon or a straw
3. Do some more science
Another trick is to use different liquids to make a density column
Find a tall, thin glass or tube and add a layer of honey to your container
Carefully squeeze in a layer of washing up liquid
Next add a layer of coloured water (dribble it slowly down the side to avoid spoiling the layers)
Lastly add a layer of oil
Enjoy the beautiful coloured layers but definitely don’t put this one on your salad!
What’s going on? The science in a sentence… Oil and water-based liquids like vinegar don't mix (the technical term is immiscible); when you shake it, small vinegar droplets are temporarily suspended in the oil - but they will seperate out again in time.
Oil floats on the top of the water/vinegar because it is less dense. Density is a measurement of how much matter is in a given volume or how much stuff is packed into a given space. Imagine a jar stuffed full of marshmallows – if you take some out and eat them, the contents are less densely packed in – there is less matter in the same space.
Even for liquids that will mix, we can use different densities to create the tower of layers – we love this sugar solution rainbow in a jar.
In our tower, the most dense liquid (honey) is heavy and stays sunk at the bottom; the next most dense is the washing up liquid; the water floats on top of that and finally the oil floats on top of the water because it is the least dense.
For the unmixables experiment, we used vegetable oil and balsamic vinegar to get contrast but any vinegar will work. My kids like this simple cheese salad but you could go gourmet and use feta, onion and olives to make a Greek salad. The honey and mustard dressing also goes well with grilled chicken.
To avoid wasting ingredients for the density column, a small tube is ideal. If you have a science set, it may have a test tube or a measuring cylinder. We repurposed a medicine syringe and sealed the bottom with some sticky tack.
If you are feeling ambitious, you could try making a rainbow coloured density tower from different liquids. Try different syrups, coloured alcohols and flavoured oils to get the range of colours.
Grown-ups may find this activity a good use of that green Crème de Menthe or blue Curacao lurking at the back of the spirits cupboard (check out this list of alcohol densities to plan your creations).
Image courtesy of Pexel