Question

a mixture of kclo3 and an inert impurity nacl weighs 1.75gm. it was heated unit decomposition of the kclo3 was complete. (nacl was not affected by the heating) after cooling, the mixture weighed 1.11 grams.

a)write a balanced equation for the decomposition reaction.

b) how many grams and moles of O2 were produced in the decomposition?

c) how many grams and moles of kclo3 were present in the original mixture?

d)calculate the % kclo3 in the original mixture?

Answer 1

Ans :

a) The balanced reaction is given as :

2KClO3 (s) = 2KCl (s) + 3O2 (g)

b)

Mass of produced in decomposition = initial mass - final mass

= 1.75 g - 1.11 g = 0.64 g

Number of moles of O2 produced = mass / molar mass

= 0.64 / 31.999

= 0.02 mol

c)

3 mol O2 is produced when 2 mol of KClO3 decomposed

So if 0.02 mol O2 produced , then number of mol of KClO3 in sample :

= ( 0.02 x 2) / 3

= 0.013 mol KClO3

Mass of KClO3 = mol x molar mass

= 0.013 x 122.55

= 1.634 grams

d)

% KClO3 = ( mass of KClO3 / total mass) x 100

= ( 1.634 / 1.75) x 100

= 93.4 %