Susan's Homeschool Blog

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Today we are doing a fun saltwater experiment where we freeze water with different amounts of salt to see which solution freezes faster. Yes, it’s like a race to see which freezes first! This experiment is from Christian Kids Explore Chemistry by Bright Ideas Press, and we have been working our way through the fun experiments in this book.

First you will want to get four plastic cups and label them by writing on a piece of paper with a black marker. We attached the labels to the plastic cups with packing tape. These are the labels:

• Water
• 1 teaspoon salt + water
• 2 teaspoons salt + water
• 3 Teaspoons salt + water

Pour water into the four glasses and measure the correct amount of salt to put into each glass. Stir the solutions until the salt has dissolved. Now place them all in the freezer. If your freezer is a drawer like mine, you will need to lodge the glasses in place with a frozen lasagna or other large froze object. (Watch the video to see how I kept the glasses from falling over in the freezer.)

Which glass of water will freeze first?

After two hours, the glass with only water in it was solid ice. The glass with one teaspoon of salt in the water was a little less solid than the first glass. You could scrape it like a snow cone because it wasn’t completely solid. The glass with two teaspoons of salt was even less frozen, and the one with three teaspoons of salt was not frozen at all when I broke through a thin layer of ice on the top. Under that thin layer of ice was liquid.

The more salt that you have in the water, the longer it takes to freeze. After four hours, all the glasses were more frozen, but the one with three teaspoons of salt was still quite liquid.

After 24 hours, we checked the glasses again, and all of them were finally solid. Take a look:

So what does this mean? Salt lowers the temperature at which water will solidify, so when you are making ice cream, for example, you can put salt on the ice to keep the ice cold longer.

You can also use salt to melt snow in your driveway in the winter.

This post contains affiliate links. I was compensated for my work in writing this post.

My kids tested Charles’s Gas Law with a fun experiment involving a glass soda bottle and a balloon. We are using Christian Kids Explore Chemistry by Bright Ideas Press. This is one of the experiments in the book.

What is Charles’s Gas Law?

I suppose we should define Charles’s Gas Law before we conduct our experiment. Charles’s Gas Law: If the temperature of a gas is increased, the volume of the gas will increase.

Knowing this law will help you predict what will happen when you place a glass bottle in the refrigerator, then set it in a bowl of boiling water with a balloon over it. The gas inside the bottle went from cold to hot, which means the air inside the bottle is expanding. This is the reason the balloon immediately stands up, because the expanding air needs to go somewhere.

Then you place the bottle into ice water, and see the balloon deflate again. You might need to place it in the refrigerator to see the full effect of the deflated balloon.

Steps for Charles’s Gas Law Experiment

1. Place a glass bottle into the refrigerator for at least one hour so the air inside it is nice and cold.
2. Place some hot (not boiling–it melted our first balloon!) water in a bowl, and place ice water in another bowl.
3. Grab the bottle out of the refrigerator and put the balloon on the top of it.
4. Place the bottle into the hot water and watch the balloon stick up suddenly.
5. Now place it into the ice water. Wait for a while, and notice there is less air pressure in the balloon.
6. Place the bottle back into the fridge, and an hour later, voila! A limp balloon will cause your kids to squeal and point. Indeed, Charles’s Gas Law is correct!

Video of the Experiment

Take a look at the experiment:

The bottle is too small to actually inflate the balloon for real, but I’ve done a similar experiment, throwing dry ice into the bottle and placing a balloon over the top. The air expands way more explosively, and the balloon actually inflates!

*Always make sure to wear gloves when touching dry ice.*

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What happens when you have weird-shaped objects, and you want to know their volume? Find out a clever way to do just that! We will be measuring the volume of a solid in our experiment today. My younger two children are using Christian Kids Explore Chemistry by Bright Ideas Press, and this is one of the fun experiments in the book.

Grab three interesting-shaped rocks from your backyard, and label them A, B, and C with a permanent marker. Grab a glass measuring cup and pour 300 ml of water into it. Now you will want to place one rock into the water. Measure how much the water went up. How high is the water now? Write it down. Then subtract the number from the original number (300 ml). You will find out the volume of the rock! Whatever amount of water the rock displaced is the amount of space it filled up, or its volume.

Remove Rock A from the water and measure Rock B in the same way. Was the rock smaller, larger, or the same volume? What about Rock C? Our third rock had the largest volume of the three rocks.

Measuring the Volume of a Solid Experiment

Now you can see how we performed this fun experiment:

Make sure to write down each of your measurements on the chart provided in the book. It helps if you clip the page to a clip board so that you can write your measurements as you are doing the experiment. If you want, you can doodle all over the rest of your page, as if you were a mad scientist!