Question

0.0833 mol of carbohydrate of empirical formula CH2O contains 1 g of H2. the molecular formula of the carbohydrate is

Answer 1

Answer: The molecular formula for the carbohydrate is $C_6H_{12}O_6$

Explanation:

We are given an empirical formula for the carbohydrate which is $CH_2O$. The carbohydrate can be written as $(CH_2O)_n$

By Stoichiometry:

1 mole of a carbohydrate contains = $2n\times 1g=(2n)g$ of hydrogen

So, 0.0833 mole of carbohydrate will contain = $\frac{2n}{1}\times 0.0833=0.1666n$ grams of hydrogen

It is given that the the mass of hydrogen in 0.0833 moles is 1g

Equating both the quantities, we get:

$0.1666\times n=1\\n=6$

Thus, the molecular formula for carbohydrate will be $(CH_2O)_6=C_6H_{12}O_6$

Answer 2

Molecular formula is a multiple of empirical formula. That is, in the given case, if the empirical formula is CH2O, the molecular formula can be written as n(CH2O) or, CnH2nOn.

Using this molecular formula, we can see that each mole of this carbohydrate contains n moles of carbon, 2n moles of hydrogen and n moles of oxygen.

Given number of moles of carbohydrate = 0.0833 moles

number of moles of hydrogen in this given amount = 2n x 0.0833 moles.

It is given that 0.0833 moles of carbohydrate contains 1 g hydrogen. This means that 2n x 0.0833 moles of hydrogen contain 1 g of hydrogen.

Since, the molar mass of hydrogen is 1 g/mol,

2n x 0.0833 mol x 1 g/mol = 1 g

solving the equation, we get, n = 6.

Thus, the molecular formula of the carbohydrate is C_6H_12O_6 , which is the molecular formula of glucose.

We can verify our answer.

0.0833 moles of glucose contains 12 x 0.0833 moles of hydrogen, which is equal to 1 g of hydrogen, as given in the question.

Hope this helps.