Paper 2- Mole calculations

Question 1

How do you work out the relative formula mass (Mr) from the relative atomic mass (Ar)

e.g. MgCl2

Answer 1

Ar of Mg= 24
Ar of Cl= 35.5

24 + (35.5x2) = 95

Mr- MgCl2= 95

Question 2

what is the formula to work out mass, moles and mr

Answer 2

mass

mol x mr

Question 3

How do you work out the empirical formula

Answer 3

1) list all elements in the compound
2) underneath them write experimental masses
3) find number of moles of each element by dividing each mass by Ar
4) divide by smallest
5) multiply to get whole numbers

Question 4

molecular formula steps

Answer 4

mr
empirical mass

empirical formula x answer

Question 5

solutions and concentrations formula

Answer 5

mol

vol x conc

Question 6

water of crystallisation steps

CaCl2.xH20

Answer 6

1) list the salt and water
2) write experimental masses
3) divide by mr
4) divide by smallest

Question 7

reacting masses calculation steps

e.g. find mass of iron produced when 44.8g of iron oxide is reduced by carbon monoxide:

Fe2O3 + 3CO –> 3CO2 + 2Fe

Answer 7

1) find data
2) convert to moles
3) use ratios from equation
4) answer ques using appropriate moles equation

Question 8

gas volumes formula

Answer 8

volume

moles x 24000

Question 9

gas volumes calculation steps

Answer 9

1) find moles
2) use ratios from equation
3) answer ques using appropriate moles equation

Question 10

titration calculation formula

Answer 10

mol

vol x conc

Question 11

titration calculation steps

Answer 11

1) work out the moles
2) use ratios
3) work out concentration/ volume

Question 12

percentage yield equation

Answer 12

actual yield/ theoretical yield x 100