Question

The % composition of a substance is P =32.63 , 0 =16.82 & S = 50.55. The V.D of substance is 190. Find the molecular formula of the substance .


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Answer 1

Given info : the percentage composition of a substance is P = 32.63 % , O = 16.82 % and S = 50.55 % and also vapor density of the compound is 190.

We have to find molecular formula of compound.

solution : first find percentage composition/atomic mass ratio of each substance.

P ⇒32.63/31 = 1.05258

O ⇒ 16.82/16 = 1.05125

S ⇒50.55/32 = 1.57968

Now find simple ratio of above terms

P : 0 : S = 1.05258 : 1.05125 : 1.57968

= 1.00 : 1.00 : 1.5

= 2 : 2 : 3

So the emperical formula of compound is P₂O₂S₃

Given vapor density = 190

So, molar mass of compound = 2 × 190 = 380

now n × emperical formula mass = molar mass

⇒n × (31 × 2 + 16 × 2 + 32 × 3) = 380

⇒n × (62 + 32 + 96) = 380

⇒n × 190 = 380

⇒n = 2

So, molar formula is 2(P₂O₂S₃) = P₄O₄S₆