Question

a compound contains 92.3% carbon and 7.7% hydrogen. its molecular mass is 18u. Establish its empirical formula and molecular mass?

Answer 1

molecular formula is C2 H2 and empirical formula is C1 H1. if you like this answer please add a comment and place a thank you

Answer 2

The molecular formula and empirical formula for a compound with 92.3% Carbon and 7.7% hydrogen is CH.

To calculate the molecular formula of given compound the following steps must be followed:

Step 1: Find the moles of each constituents present in the compound.

Step 2: Divide each mole value with the smallest mole value obtained.

Step 3: Write the empirical formula

Step 4: Calculate the molar mass of empirical formula.

Step 5: Divide the given molar mass with the Empirical formula molar mass.

Step 6: Multiply each subscript of the empirical formula with the obtained answer.

Step 7: Molecular formula is obtained.

Base on the given data it is inferred that:

Carbon = 92.3g

Hydrogen = 7.7g

Step 1:

Number of moles of Carbon = $\frac{Given mass}{Molar mass} = \frac{92.3}{12.0107}= 7.6848$

Number of moles of hydrogen = $\frac{7.7}{1.00794} = 7.6393$

Step 2:

Smallest mole value obtained is 7.6393

∴

C = $\frac{7.6848}{7.6393} = 1.005 = 1$

Step 3:

The empirical formula for the given compound is CH.

Step 4:

Molar mass of the empirical formula = 1(12)+1(1) = 13

Step 5:

$\frac{Molecular mass}{Empirical formula mass} = \frac{18}{13} = 1.38=1$

Step 6:

As the obtained value is 1, the molecular formula of the given compound is same as that of the empirical formula which is CH.

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