Question

BASIC CONCEPTS OF CHEM. (CLASS 11)

A hydrocarbon gives upon combustion 0.72 g of water and 3.08g of CO2. The empirical formula of the hydrocarbon is:

(a) C2H4

(b) C3H4

(c) C6C6

(d) C7H8

Answer 1

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and the Solution is:-

General equation for combustion of hydrocarbon:

CxHy + (x+ y/4)O2 → xCO2 + (y/2)H2O

Number of moles of CO2 produced = 3.08/44 = 0.07

Number of moles of H2O produced = 0.72/18 = 0.04

SO, x / (y/2) = 0.07/0.04 =  7/4

The formula of hydrocarbon is C7H8

Hence, the correct option is (d)

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Answer 2

Hey there!

We know,

Hydrocarbon contains C and H. Let he formula be $C_xH_y$

 And

18 g of H₂O consist of 2 moles of H atoms.

Then, 0.72 g of H₂O consist of:

2/18 x 0.72 = 0.08

So, 0.72 g of H₂O consist of 0.08 moles of H atoms.

We know,

44 g of CO₂ consist of 1 mole of C atom.

Then, 3.08 g of CO₂ consist of:

1/44 x 3.08 = 0.07 

So, 3.08 g of CO₂ consist of 0.07 mole of C atom.

Then, ratio of x and y :

= 0.07/0.08 

= 7 : 8

So, empirical formula is C₇H₈.

Hope It Helps You!