relative formula mass

Question 1

find the relative formula mass(Mr) of MgCl2

Answer 1

relative atomic mass(Ar) of Mg = 24
Ar of Cl = 35.5
24 + (2 * 35.5) = 95
So Mr of MgCl2 = 95

Question 2

Find the Mr of H2SO4

Answer 2

Ar of H = 1
Ar of S = 32
Ar of O = 16
(2 * 1) + 16 + (4 * 16) = 82
So Mr of H2SO4 = 82

Question 3

What is the formula of percentage mass of an element in a compound

Answer 3

percentage mass of total relative / Mr of the
an element in a = atomic mass of / compound. * 100
compound that element /

Question 4

calculate the percentage by mass of calcium in calcium chloride (CaCl2)

Answer 4

Mr of CaCl2 = 111. Ar of Ca = 40
40/111 * 100 = 36%

Question 5

rearrange the percentage mass formula to make total relative atomic mass the subject

Answer 5

percentage mass of Mr of the / total relative
an element in a * compound / 100 = atomic mass of
compound / that element