Sodium hydroxide

Sodium hydroxide is probably the best known STRONG ALKALI. It is pH 11. If you see it as one of the products in a reaction, you will know that the solution has become alkali.
If you think about it, the pH has gone UP. pH11 is UP from pH7. The pH goes DOWN to make acids.

Intermolecular forces

Water has a low boiling point because the forces between the molecules are weak. On the diagram, the forces between H and O are strong covalent bonds. It takes a lot of energy to break up water into H and O. However, it is easy to separate the molecules. In an exam answer, you need to make it clear that it is the inter-molecular forces that you are talking about.

Metallic bonding

Metals have big atoms and so the force of attraction between the nucleus and the outer electrons is weaker. The electrons can wander off. Metals contain positive ions surrounded by delocalised free electrons.
Metallic bonding is shown in the diagram. Ion A pulls left on the free electrons (green arrow). Ion B pulls right on the free electrons (red arrow). Like two kids fighting over a toy, the ions are held together.

The difference between yield and rate of reaction

This is bugging me a bit, but I think it boils down to this:

Yield means what percentage of the reaction ends up doing what you want. Remember that if it is a reversible reaction, it can make the product and then undo it again.

Rate of reaction means how fast the reaction goes; how quickly you get what you want.

Questions dealing with pressure be about either:

• If you increase the pressure you push the particles closer together so that they collide more often and the rate of reaction increases.
• If you increase the pressure of a reversible reaction involving gases, you favour the direction that goes from more molecules to less molecules. If that is the forward direction, then increasing the pressure will increase the yield.

It is the same with temperature:

• If you increase the temperature, the particle move faster and so collide more frequently. More collisions reach the activation energy. Hence the rate of reaction increases.
• If a reversible reaction is endothermic in the forward direction and you increase the temperature, then you will increase the yield.

Kinetic energy

This is the energy that an object has when it is moving.

You can calculate knietic energy like this:

kinetic energy = 1/2 x mass x speed x speed

For example:

A 500kg car is travelling at 10 m/s.

kinetic energy = 1/2 x 500 x 10 x 10 = 25000 Joules

momentum

Momentum means how difficult it is to stop an object that is moving.

The bigger the momentum the harder it is to stop.

Momentum = mass x speed

Momentum is measured in kgm/s

Momentum can be passed on from one object to another in a collision.

Remember the clicking balls!

Precipitation reactions

This when you mix two liquids together and end up with a solid floating in the liquid. The solid is called a precipitate.

We did it when we made the chemical that they put on film. We got a white precipitate which we filtered out. We spread the white precipiate out on the filter paper and put it on the side in the sunshine with a coin over it.

Where the sun reached it, a reaction happened and the chemical went dark grey. Under the coin there was no light and no reaction so it stayed white.