section 3

Question 1

equilibrium

Answer 1

This is a dynamic equilibrium, not a static equilibrium. It’s not that everything has stopped - it’s that both of the reactions are still happening, just exactly the same amount.

Question 2

Number of moles

Answer 2

=Volume of gas/ 24 dm3

Question 3

so when it comes to volumes…

Answer 3

What this means is - say you’re told the 10 cubic decimetres of gas A, turns into 5 cubic decimetres of gas B and 7.5 cubic decimetres of gas C you equation would be: 10A→5B+7.5C which you could then simplify to 4A→2B+3C without having to know anything about the mass or the moles.

Question 4

Valency

Answer 4

Valency means “combining power” - essentially the “number of links” an element can form with other things. Different elements have different valencies, depending on which group of the periodic table they’re in. Here’s a really, really useful table that you need to learn off by heart.

Question 5

Separating Funnel

Answer 5

We use separating funnels to separate immiscible liquids. Immiscible means that the liquids do not mix - just like oil and water - because of differences in their densities and differences in their chemical bonding properties. Oil is unable to form hydrogen bonds with water molecules, whilst the water molecules form strong hydrogen bonds with other water molecules. This means that oil will never mix with water.

When the mixture settles, you will find two distinct layers of liquids. By controlling the flow of liquid out of the separating funnel using the stopper, you can drain off both liquids into separate beakers.

Question 6

Fractional Distillation

Answer 6

When liquids are miscible, they will mix togther and not settle into distinct layers. We can’t use separating funnels now - instead, we need to make use of the fact that the different liquids have different boiling points due to the different chemical bonds formed between molecules of liquid.

Imagine a mixture of liquids A and B mixed together. Liquid A has the lower boiling point. When we heat the mixture, we will find that the temperature (measured at the thermometer - see diagram) will hold steady at the boiling point of the liquid A. This means that the vapour of liquid A has reached the top of the fractionating column, heating the beads in the column up to roughly the same temperature. However, when the vapour of liquid B comes into contact with the beads of the fractionating column, it can still condense to liquid and fall back into the beaker because it has a higher boiling point than liquid A.

Question 7

Paper Chromatography

Answer 7

We use paper chromatography to separate the components of a mixture based on their rate of diffusion through the paper. The movement of the substance along the paper depends on:

The attraction of the substance to the stationary phase - the greater the strength of attraction to the paper, the less the substance will move
The attraction of the substance to the solute phase - the greater the srength of attraction to the solvent, the further the substance will move
This topic of chromatography is covered in greater detail in the tutorial on chromatography.