RELATIVE FORMULA MASSES (Mr and Ar)

The relative atomic mass is the average mass of an atom compared to 

• the mass of a carbon-12 atom.
• 1/12 the mass of a carbon-12 atom
• the mass of a hydrogen atom
• 1/12 the mass of a hydrogen atom

What is the relative formula mass of ammonium nitrate, NH4NO3 ?

[Relative atomic mass: N, 14; H, 1; O, 16]

• 76

• 79

• 80

• 90

Calculate the relative formula mass of

aluminium sulphate, Al₂(SO₄)₃

[Relative atomic mass:

O = 16 ; Al = 27 ; S = 32 ; Cl = 35.5 ; Cu = 64 ]

(a)  

What are the four state symbols and what do they stand for?

• (s) solid (l) liquid (g) gas (aq) aqueous

• (S) solid (L) liquid (G) gas (Aq) aqueous

• (so) solid (li) liquid (ga) gas (aq) aqueous

• (So) solid (Li) liquid (Ga) gas (Aq) aqueous

What is relative formula mass?

• The sum of the relative masses of each atom in a compound

• The multiplication of the relative masses of each atom in a compound

• The division of the relative masses of each atom in a compound

• The average of the relative masses of each atom in a compound

What symbol do we use for relative formula mass?

• M_r

• A_r

• RM_r

• RFM_r

Calculate the Mr of Ba(OH)₂

• 137 + 16 + 1 = 154

• 137 + (16+1)x2 = 171

• 137 + (16+1)x3 = 188

• 137 + (16 x 2) + (1 x 2) = 177

Calculate the relative formula mass (Mr) of lithium oxide (Li₂O).

Relative atomic masses (Ar):

 Li = 7 O = 16

• 23

• 30

• 39

Calculate the relative formula mass (Mr) of magnesium chloride (MgCl₂).

Relative atomic masses (Ar):

magnesium = 24; chlorine = 35.5

• 95

• 94

• 59.5

• 60

Calcium carbonate reacts with nitric acid to produce calcium nitrate.

Relative atomic masses (Ar): N = 14; O = 16; Ca = 40

Calculate the relative formula mass (M_r) of

calcium nitrate, Ca(NO₃)₂

• 164

• 102

• 204

• 160