1. mass - mass relationship
  2. mass - volume relationship
  3. volume - volume relationship
  4. mass - volume - number of molecules relationship etc.,
Eg-1: Al (s) + Fe2 O 3(s) ----> Al 2 O3 (s) + Fe (s) (atomic masses of Al = 27U, Fe = 56U, and O = 16U)

2Al (s) + Fe2 O 3(s) -----> Al2 O 3(s) + 2Fe (s) , is a balanced equation

(2x27)U + (2x56+3x16)U ----> (2x27+3x16)U + (2x56)U

54 U + 160 U ----> 102 U + 112 U

or 2 mol + 1 mol -----> 1 mol + 2 mol

54 g + 160 g -----> 102 g + 112 g

Suppose that you are asked to calculate the amount of aluminium, required to get 1120 kg of iron by the above reaction.

Solution: As per the balanced equation

Aluminium ---> Iron

54 g –––––> 112 g

xg –––––> (1120 x 1000)g

∴ x g = (1120x1000)g x 54 g/112g

= 10000 x 54 g

= 540000 g or 540 kg

∴ to get 1120 kg of iron we have to use 540 kg of aluminium.

Eg-2: Calculate the volume, mass and number of molecules of hydrogen liberated when 230 g of sodium reacts with excess of water at STP.(atomic masses of Na = 23U, O = 16U, and H = 1U)

The balanced equation for the above reaction is,

2Na (s) + 2H2 O (1) –––––> 2NaOH (aq) + H2(g)

(2x23)U + 2(2x1+1x16)U => 2(23+16+1)U + (2x1)U

46 U + 36 U –––––> 80 U + 2 U

Solution: As per the balanced equation:

46g of Na gives 2g of hydrogen

230g of Na gives ______? g of hydrogen.

230 g x 2g/46g = 10g of hydrogen



page no:29

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