

InterviewSolution
Saved Bookmarks
1. |
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, what is the empirical formula of the carbohydrate? b. If 0.0833 mole of the carbohydrate contains `1.0 g` hydrogen , what is the molecular formula of the carbohydrate? |
Answer» Step I. Calculation of the empirical formula of carbohydrate Percentage of carbon `= ("Mass of carbon")/("Mass of carbohydrate")xx100=(("124 g"))/(("310 g"))xx100=40` Percentage of water `= 100-40=60` `{:("Element/Compound","Percentage","Atomic mass (Molar mass)","Atomic ratio (Molar ratio)","Simplest whole no. ratio"),("Carbon (C)",40,12,(40)/(12)=3.3,1),("Water"(H_(2)O),60,18,(60)/(18)=3.33,1):}` Empirical formula : `C_(1)(H_(2)O)_(1) or CH_(2)O` Step II. Calculation of the molecular formula of carbohydrate 0.0833 mole of carbohydrate contains H = 1.0 g or 1 atom 1 mole of carbohydrate contains H atom `= (("1 atom"))/(("0.0833 mol"))xx"1 mol"=12` atoms Thus, 1 mole and also one molecule of carbohydrade contain hydrogen atoms = 12 Since hydrogen and oxygen are present in the ratio of 2 : 1 therefore, 1 molecule of carbohydrate contain oxygen atoms = 6 `:.` Molecular formula of carbohydrate `= (CH_(2)O)xx6 = C_(2)H_(12)O_(6)`. |
|