Solutions

We're on to Term 2 Chemistry now, and the first topic is... solutions! No, not solutions as in answers, but solutions as in homogeneous mixtures. (If you can't remember what a homogeneous mixture is, go to my post about Classification of Matter.)

This is another topic I'm going to go through dot point at a time since the dot points don't follow on from each other that well.

Identify, explain and give examples of saturated, unsaturated and supersaturated solutions

To make things a bit less wordy for me to explain, here's some terminology for you. The solute is the substance that dissolves. The solvent is the substance that the solute dissolves in. For example, when you dissolve salt in water, salt is the solute and water is the solvent.

A saturated solution has the maximum amount of solute that the solvent can hold at that temperature. An unsaturated solution has less than the maximum amount while a supersaturated solution has more than the maximum amount.

But wait, you may ask. How can you have a solution containing more than it can dissolve? Well, you see, generally solubility increases with temperature (if I remember correctly, the exceptions are mainly gases which have decreasing solubility with increasing temperature). If you heat up the solvent and dissolve the solute, sometimes most of the solute will stay dissolved in the mixture even as it cools down. This is one way you can get a supersaturated solution. I'm sure there are other ways, but I don't know what they are.

By the way, I was curious as to why solubility increases with temperature, so I Googled it. It seems that increased temperature makes the particles of the solvent spread apart more, allowing more room for other substances to be mixed in to the solution.

Apply solubility rules to predict when two dilute ionic solutions are mixed

When two ionic solutions are mixed, generally what happens is that anions (negative ions) of the two ions swap places (or the cations/positive ions, if you prefer). For example, when NaCl and AgBr are mixed, the resulting products would probably be NaBr and AgCl. To check their solubilities, just look at the solubility table on your data sheet. I don't think I have to explain how to read a table... I hope I don't have to explain, anyway.

Use the colour of ions to identify reactants and the products in chemical processes

The main thing here is just to be logical and use process of elimination or whatever to figure out what the ions are. I don't have an example to show you though.

Explain colligative properties including the effect of concentration on vapour pressure, melting point and boiling point of a solution

This is something I need to revise. Stay tuned...

Describe the characteristics of strong/weak/non-electrolytes and give examples

Strong electrolytes completely dissociate or ionise in water. Weak electrolytes partially dissociate or ionise in water. Non-electrolytes don't ionise in water.

The difference between dissociation and ionisation is as follows: dissociation is when ions break up in water, while ionisation is when a neutral particle breaks up in water and becomes ions. Just remember that you can't ionise something that's already an ion.

Now for examples. Strong acids and ionic compounds are all strong electrolytes. Even insoluble ionic compounds are considered to be strong electrolytes, if I remember correctly. Weak acids and bases are examples of weak electrolytes. Hydrocarbons (substances containing mainly hydrogen and carbon) are examples of non-electrolytes.

Explain the difference between concentrated and dilute solutions of strong and weak electrolytes

In chemistry, there's a difference between concentration and strength. Concentration is how much of the solute you have in that amount of solvent. Strength is how much the solute dissociates or ionises. A 0.1M solution of HCl is a dilute solution of a strong acid- dilute because there isn't much HCl in the solution, but strong because HCl completely ionises in water. Meanwhile, a 6M solution of acetic acid is a concentrated solution of a weak acid- concentrated because there's lots of acetic acid, but weak because acetic acid doesn't completely ionise in water.

When I feel like it, I'll go back and find out more about how concentration affects properties of solutions. But until then, TTFN!