C4

Question 1

Relative masses and moles

Answer 1

Number of moles = mass/Ar or mass/Mr

Mass = number of moles x Ar or Mr

Percentage by mass = mass of element/mass of compound x 100

Question 2

Equations and calculations

Answer 2

Number of moles = mass of substance/molar mass

Mass = number of moles x molar mass

Question 3

The yeild of a chemical reaction

Answer 3

The percentage yeild of a chemical reaction shows how much product was actually made compared with the amount of product that was expected.

Percentage yeild = mass of product made/ maximum mass of product x100

Factors effecting percentage yeild:
Reaction could be reversible
Some products may be lost
The reaction may not be pure

Question 4

Atom economy

Answer 4

Atom economy is a measure of the efficiency of a chemical reaction.

It is the amount of starting materials that end up as useful products
If most of the starting materials end up as useful products the reaction is aaid to have a high atom economy

Atom economy = mass of desired products / sum of mass of all products x100

Question 5

Limiting reactants

Answer 5

The reactant that gets used up first in a chemical reaction is called the limiting reactant

The amount of chemicals formed in a chemical reaction are determined by the limiting reactant

Question 6

Expressing concentrations

Answer 6

Vol in dm3 = vol in cm3 / 1000

Concentration(mol/dm3) = moles/volume(dm3)

Concentration(g/dm3) = amount of solute(g)/ volume of solution(cm3) x1000

Question 7

Titrations

Answer 7

An acid and an alkali react togther and neutralise eachother. They form a salt and a water in the process.

If you mix a strong acid and a strong alkali the solution made will be neutral only if the exact quantities are added

Question 8

Acid and alkali titrations

Answer 8

If you start with more acid than alkali, the alkali will be neutralised, however the solution after will ve acidic, because the acid is in excess.

If you you have more alkali than acid to begin with, then all the acid will be neutralised and the solution left alkaline.

End point- the point in a titration where the reaction is complete and the titration should stop

Question 9

Volume of gases

Answer 9

At room temperature and pressure, one mole of any gas has a volume of 24dm3 (molar mass volume)

Number of moles of gas = volume of gas/24dm3

Volume of gas(cm3)/240000cm3