I.
Physical Science - Solutions and Solubility
Solutions
1.
How solutions form?
A.
What is a solution?
A homogenous mixture containing particles that cannot be seen, even with a microscope.
Remember solutions can be solids, liquids, or gas
Example: a.
Salt Water is a solution made up of salt and water.
However you cannot see the salt. b.
Soda – carbon dioxide is dissolved in water and syrup c.
Salt water demonstration i.
What happens to the salt when it is added to the water?
1.
It dissolves
2.
A substance that causes something to dissolve is called a solvent
3.
The something that is being dissolved is called a solute
4.
So, a solvent is a substance that dissolves a solute
B.
Dissolving
How does the process of dissolving work? a.
Dissolving of a solid in a liquid occurs at the surface of the solid and continues until the solid is in solution b.
Let’s use sugar as an example: i.
When sugar is added to water the particles that make up water are moving and cluster around the sugar molecule.
1.
Why? Because both water and sugar are polar molecules so the oppositely charged ends of water and sugar are attracted to each other. ii.
The water molecules pull the sugar molecules into solution iii.
The moving water molecules spread the sugar molecules out equally throughout the solution
Rate of dissolving a.
Does everything dissolve at the same rate? NO b.
Can you increase or decrease the rate of dissolving?
YES!!! c.
How?

d.
Sugar Cube Demonstration e.
Three ways to increase the rate of dissolving i.
Stir it – bring more fresh solvent in contact with the solute ii.
Heat it – speed up the movement of the particles increase the rate and speed of contact between the particles iii.
Grind it up or reduce surface area/volume – This increases the surface area in which the solvent can act upon the solute f.
Gases and Stirring: i.
How do you think these same factors will affect a gas-liquid solution?
1.
What happens when you shake or stir a soda? a.
The soda spills all over the place because the gas is coming out of the liquid.
2.
Will the gas come out of the soda if you do not shake or stir the soda? a.
Yes, however not as fast b.
Conclusion: Stirring and shaking a liquid-gas solution will increase the rate that gas will escape. g.
Temperature and Pressure: i.
Question: How might you cause the gas to dissolve faster in a liquid?
1.
Think about a soda, when you open a cold bottle and a warm bottle of soda which one makes a louder noise? a.
The warm one, why? i.
Gas is more soluble in colder temperatures so it will stay in solution longer than warmer temperatures. b.
Remember Charles’ Law, if you increase the temperature you increase the volume.
The warmer the temperature the more active the molecules the more likely the gas will exit the solution.