Home Experiment #4: All About Solutions
What do Kool-Aid, salt water, and rock candy have in common? They can all be made with solutions!
A solution is a mixture. In a solution, the solute is evenly spread throughout the solvent.
Let’s think about salt water. Take a cup of water and add a few grains of salt. Mix it up! The salt (or some of it, anyway), should “disappear”. It hasn’t actually disappeared, though; the salt molecules are now spread throughout the water molecules! In this case, salt is the solute and water is the solvent.
If you add salt a little bit at a time, and mix it up completely, it should keep disappearing...until it doesn’t any more! Once the water is saturated, or full, the salt will start to settle on the bottom, or precipitate.
There are a lot of fun activities you can do with solutions! Make sure you work safely and with a parent’s supervision.
4A: Solute and Saturation
How does the type of solute affect saturation? First, make a prediction. Then, try mixing a few different types of solute into water. You can try salt, sugar, Kool-Aid mix, Gatorade mix, jello mix, or any other powder you can find in the kitchen!
Which solute dissolved the most easily? Did this match your hypothesis?
Which solute was able to dissolve in the largest amount in water (has the highest solubility)? Did this match your hypothesis?
What similarities and differences were there between the most and least soluble solutes?
Challenge: Can you run the same experiment with a different solvent? How does polarity affect solubility? Can you use what you know about polarity to find a substance that would dissolve better or worse in water?
4B: Temperature and Saturation
How does the temperature of the water affect saturation? First, make a prediction. Then, mix a few grains of salt into a pot of water until the salt dissolves. Keep adding salt, counting how much you’ve added, until it stops dissolving and salt starts precipitating out of the solution. Turn on the stove and add a little heat. Can you make the salt dissolve?
What happens if you add more heat? More salt? Did this match your hypothesis?
What might happen with another solute or solvent?
What happens if you let the solution cool down again.
4C: Rock Candy and Supersaturation
As you saw in Experiment 4B, warmer water can dissolve more solute. When the water cools down again, its ability to dissolve solute drops again, and solute begins to precipitate out. We can control this precipitation to form crystals, like rock candy! Yum! Give this recipe a try, and if it doesn’t work out the first time, think about ways you can improve it. Use the Engineering Design Cycle!
4D: Separating Mixtures
You have a mixture. Maybe it is a cup of salt water or a glass of Kool-Aid. How do you separate the solute from the solvent? You can try cooling it down, but what if that doesn’t work? You can even pass it through a filter, like a coffee filter, but what if that doesn’t work? One way is to evaporate the solvent! Leave the cup out on a surface for a day or two. What happens?