Science Experiments: Solubility of Different Substances

Mavi and I got the chance to work on some experiments last weekend due to bad weather.  First we started off with a simple test of which substance dissolves in water. 

Objectives:

• Discovering which substance dissolves in water
• Why the said substance dissolves faster in water

Materials needed:

• salt, sugar, flour, chalk powder
• 4 bottles of water
• teaspoon
• stirrer

Procedure:

Findings:

1. Salt and sugar easily dissolved in water after stirring.  They have grainy texture and are crystalline thus making it more soluble in water.
2. Flour and chalk powder partially dissolved, most of the powdered portion resided at the bottom of the bottles.  They have powdery and dry texture, thus making it hard to dissolve in water.

FOR OLDER KIDS
Now, for older children who can grasp complex explanation… I prepared a visual and hands-on demonstration for Mavi to understand how the substance are more soluble, partially soluble and insoluble.  Make sure though that when you try to discuss this with your kids, he/she is already familiar with the elements in the periodic table and can understand what “attraction” means, similar to the concept of magnetism.  The link I provided is the one where I introduced the Periodic Table to Mavi in a fun and interesting way.

Anyway, here’s how the chemicals of the substance interact to water when mixed.

SOLUBLE SUBSTANCE
I used plasticine to demonstrate the chemical composition of salt and water to Mavi. 
Salt is composed of: sodium (Na+) in green  and chloride (Cl-) in purple.
Water is made up of H2O, hydrogen (H+) in white and oxygen (O-) in red.
When mixed with water, the salt molecules are easily “attracted” to the water molecules.   It’s like the positive and negative attraction in magnetism (polarity).  Thus, sodium (Na+) is attracted to oxygen (O-), while chloride (Cl-) is heavily attracted to the two positively charged hydrogen (H+).
Because of the strong attraction between molecules in the two substances, salt is easily dissolved in water.


PARTIALLY SOLUBLE
For partially soluble substances, the molecules that made up the flour or chalk have weak attractions with the molecules of the water.  Thus some have dissolved but most of it didn’t and the result are the residues found at the bottom of the bottles.

INSOLUBLE SUBSTANCE
For insoluble substances (don’t dissolve in water) like oil, the molecular contents are NOT attracted to water.  This means they do not mix with water and if you combine them, you will definitely see the separation.

Though some advanced students can explain that this is because oil is a non-polar substance and can only be dissolved with another non-polar substance, the way I explained it to Mavi is that oil molecules are just so heavy that water molecules can’t “bond” with it.

This was a fantastic activity for both Mavi and I.  More experiments coming up!
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