Mixture Types and Physical Chemical Changes
Phase Changes
Deposition: Gas into solid.
Solidification: Liquid into solid.
Mixture Types
Mechanical Mixtures
A mechanical mixture is a mixture where you can see the different parts. Examples: salad, trail mix, or sand in water.
Solutions
A solution is a mixture where the substances are evenly mixed and you cannot see the parts. Examples: salt water or sugar in tea.
Comparing Mixtures
Both are mixtures of two or more substances. The difference is that mechanical mixtures show the parts, but solutions do not.
Colloids
- They look homogeneous because the mixture appears even and you cannot easily see the different parts.
- They are heterogeneous because the particles are not fully dissolved and are still separate.
- Examples: milk, fog, or gelatin.
Distinguishing Test Tubes
First, shine a light through each test tube to tell the difference between the three types:
- The solution (calcium chloride in water) will look clear and the light will pass straight through with no beam visible.
- The colloid (water with a little milk) will look mostly clear, but you will see the beam of light because the particles scatter the light.
- The suspension (calcium carbonate in water) will look cloudy, and if you let it sit, the particles will settle at the bottom.
Density Investigations
Alcohol or Water Investigation
1. Drop an ice cube into the liquid:
- If the ice floats, the liquid is water.
- If the ice sinks, the liquid is alcohol.
This works because ice is denser than alcohol but less dense than water.
Glass and Plastic Bottles
1. Put the bottles in a tank of water.
- Plastic bottles float because they have a lower density than water.
- Glass bottles sink because they have a higher density than water.
You can quickly separate them by collecting the floating plastic and the sinking glass.
Changes in Matter
a) Wax Melting
Yes. The wax melting into liquid is a physical change because it only changes state.
b) Missing Wax
The missing wax was burned and turned into gases (like carbon dioxide and water vapour) that went into the air.
c) Wax Burning
Yes. Burning the wax is a chemical change because new substances are formed.
Deposition: Gas into solid. Solidification: Liquid into solid.
Mixture Review
A mechanical mixture is a mixture where you can see the different parts. Example: salad, trail mix, or sand in water.
A solution is a mixture where the substances are evenly mixed and you cannot see the parts. Example: salt water or sugar in tea.
Both are mixtures of two or more substances. The difference is that mechanical mixtures show the parts, but solutions do not.
Colloids Revisited
They look homogeneous because the mixture appears even and you cannot easily see the different parts. They are heterogeneous because the particles are not fully dissolved and are still separate. Example: milk, fog, or gelatin.
Test Tube Differentiation
First shine a light through each test tube.
The solution (calcium chloride in water) will look clear and the light will pass straight through with no beam visible.
The colloid (water with a little milk) will look mostly clear but you will see the beam of light because the particles scatter the light.
The suspension (calcium carbonate in water) will look cloudy, and if you let it sit, the particles will settle at the bottom.
Liquid Density Test
1. Drop an ice cube into the liquid:
- If the ice floats, the liquid is water.
- If the ice sinks, the liquid is alcohol.
This works because ice is denser than alcohol but less dense than water.
Bottle Density Separation
1. Put the bottles in a tank of water.
Plastic bottles float because they have a lower density than water. Glass bottles sink because they have a higher density than water. You can quickly separate them by collecting the floating plastic and the sinking glass.
Wax Change Summary
a) Yes. The wax melting into liquid is a physical change because it only changes state.
b) The missing wax was burned and turned into gases (like carbon dioxide and water vapour) that went into the air.
c) Yes. Burning the wax is a chemical change because new substances are formed.