Question

A 78.0 g sample of an unknown compound contains 12.4 g of hydrogen. what is the percent by mass of hydrogen in the compound?

Answer 1

Formula to find the percent composition of an element in a compound is
`\frac {MolarMassOfElement}{MolarMassOfCompound}*100`.

Now enter the variables into the formula.


`\frac {12.4}{78.0}*100 = 15.897`%
Round to 3 significant figures. 15.897% = 15.9%

The answer is 15.9% H

Answer 2

The percentage by mass of hydrogen in the unknown compound is 15.9 %

Step-by-step explanation:

The formula to be used here is

% by mass of an element in a compound =

(molar mass of the element ÷ molar mass of the compound) × 100

From the question, the mass of the element (Hydrogen) is 12.4 g

The mass of the compound (unknown) is 78.0 g

Hence,

% by mass of hydrogen in the unknown compound = (12.4 ÷ 78) × 100

= 15.9 %