Question

carbohydrates are compound containing only carbon, hydrogen and oxygen. when heated in the absence of air, these compounds decompose to form carbon and water. If 310 g of a carbohydrate leave a residue of 124 g of carbon on heating in absence of air, what is the empirical formula of the carbohydrate ?​

Answer 1

Answers;

The molecular formula of the carbohydrate is $C_6H_{12}O_6$

Explanation:

Given, Carbon present = 124g

Water present after decomposition = Total carbohydrates (in gm) - carbon present after decomposition (in gm)

                               Water present  = 310 - 124

                               Water present  = 186 gm

Number of moles in carbon(C) = 10.03

Number of moles in water( $H_2O$ ) = 10.03

Now, Taking the ratio of $C: H_2O$ = 1: 1

Molecular formula: 0.0833 moles of the carbohydrate contains 1.00g or one atom of hydrogen.

Therefore,

One mole of the carbohydrate will contains one mole of hydrogen atoms $\dfrac{1}{12} = 0.0833$                    

The number of hydrogen atoms in the molecules is 12

The molecular formula will be the 6 times for the empirical formula-$CH_2O \times 6 \\\\ C_6H_{12}O_6$

Hence, the molecular formula of the carbohydrate is $C_6H_{12}O_6$