- Two transparent containers of about the same size and shape. We used 2L coke bottles
- Vegetable oil
- Food coloring – we used 3 drops each of red and yellow food coloring mixed with 3 TBs of vegetable oil for our hot water and 3 drops each of blue and green food coloring for cold water.
Questions for Discussion Before the Experiment
- Do molecules move? My 8 year old confidently said “yes” to that, since we already talked about molecular motion when we discussed how molecules attract.
- Can you think of any way to show that molecules move? Her proposal was to mix something in water – pretty close to what I planned to do.
- What affects the speed of movement? Smarty was stumped on that, but when I changed the question and asked her if temperature affects molecular speed, she correctly answered that it does and that molecules will move faster in warm water.
Do the Experiment
Since Smarty is old enough to understand scientific method, we first discussed which variables we will control. Amount of water, amount of oil, and amount of food coloring were our control variables. Temperature was our independent variable.
The experiment itself is really 5 minute science. But, if you give my 8 year old a bottle of oil and ask to measure 3 TBS of it, she won’t think of holding it over a smaller container in case of spills. Instead she will make a giant mess, which will take 15 minutes to clean up. So our 5 minute science lesson got hijacked for a while with a practical life lesson on how we pour liquids and how we clean up oil spills. Eventually we returned to our liquid fireworks and slowly poured oil and food coloring mixture over water starting with cold water. The difference was quite dramatic – hot water turned orange very fast, but Smarty could enjoy slow fireworks in an icy cold water for a while. Eventually, she decided to “help” mixing by blowing bubbles into cold water and mixing it.
Why Don’t Oil and Water Mix?After we were done with an experiment, I asked Smarty why oil and water don’t mix. Her response was, because oil is lighter than water. I asked her then which molecule she thinks is lighter – water or oil. She responded that oil molecule must be lighter. It is an obvious misconception, so I asked her then what is lighter – a grain of sand or a pom-pom. She said that a grain of sand is lighter. Then I asked her what will happen if she fills one cup of her balance scale with sand and another cup with pompoms. She said that sand will be heavier, because there is more sand than pom-poms. I explained to her then that this is exactly what happens with water and oil – water molecules are lighter, but there is significantly more of them in any given volume than oil molecules, so the density of water is higher than the density of oil. And then we watched this playful (and more in-depth) explanation as to why oil and water don’t mix.
What science fun have you had lately?
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