relative formula mass

Question 1

relative formula mass

Answer 1

the sum of the relative atomic masses of all the atoms in a compound

Question 2

symbol for relative formula mass

Answer 2

Mr

Question 3

what is the relative formula mass for Na₂CO₃?

Answer 3

Na-23 x 2=46
C-12 x 1=12
O-16 x 3=48
Mr-46+12+48
=106

Question 4

what is the relative formula mass for Fe₂(SO₄)₃

Answer 4

Fe-2 x 56=112
S-3 x 32=96
O-12 x 16=192
Mr-112+96+192
=400

Question 5

equation for percentage mass of an element in a compound

Answer 5

Ar x number of atoms of that element/Mr of the compound x100

Question 6

find the percentage mass of sodium in sodium carbonate, Na₂CO₃

Answer 6

(2x23) + 12 + (3x16)=106
46/106 x 100 =43%

Question 7

A mixture contains 20% iron ions by mass. What mass of iron chloride (FeCl₂) would you need to provide the iron ions in 50g of the mixture?

Answer 7

1. mass of iron in the mixture
   50 x 20/100 = 10g
2. calculate % mass of iron in iron chloride
   56/56+ (2 x 35.5) x100=44.09…%
3. calculate mass of iron chloride that contains 10g of iron
   10/(44.09/100)=23 g
   so you need 23g of iron chloride to provide the iron in 50g of the mixture