Carbohydrates are compounds containing only carbon, hydrogen and oxygen having the atomic ratio of `H : O` as `2 : 1`. When heated in the absence of air, these compounds decompose to form carbon and water.
a. If `310 g` of a carbohydrates leaves a residue of `124 g` of carbon on heating in absence of air, whatis the empirical formula of the carbohydrate?
If 0.0833 mole of hte carbohydrate contains `1.0 g` hydrogen , what is the molecular formula of the carbohydrate?

Answer

A, B, C

Explanation

a. Empirical formula : Carbon present `= 124 g`
water present `= 310 - 124 = 186 g`
Moles of Carbon `= (124)/(12) = 10.03`
Moles of `H_(2) O = (186)/(18) = 10.03`
Ratio of `C : H_(2) O = 1 :1`
b. Molecular formula : 0.0833 moles of the carbohydrate contains `1.00 g` or one atom of hydrogen.
Therefore, one mole of the carbohydrate will contains hydrogne atoms `= 1//0.0833 = 12`
Number of hydrogen atoms in the molecules being 12, the molecular formula should be six times the empirical formula, i.e., `CH_(2) O xx 6` or `C_(6) H_(12) O_(6)`
Hence, the molecular formula of the carbohydrate is `C_(6) H_(12) O_(6)`.