Question

an organic compound is found to contain the following compositions:C = 92.3% and H = 7.69% determine its empirical formula. also find its molecular formula if its molecular mass is 78 Amu

Answer 1

Follow those steps :
Imagine that you have 100 g of Carbon and hydrogen
Convert % into mass
⇒
92.3
%
→
92.3
g

7.7
%
→
7.7
g
Transform mass into moles
⇒
(The molar mass of carbon and hydrogen are rounded here)
C
:
92.3
12.01
=
3 sig. fig.

7.69
m
o
l
H
:
7.7
1.01
=
3 sig. fig.

7.62
m
o
l
To see for one Carbon, how many Hydrogen you have, put the next equation
⇒
1
7.69
=
x
7.62
(It can be the other way around, for 1 Hydrogen, how many Carbon)
1
7.62
=
x
7.69
Solves for x
⇒
(Generally take the largest of those result and divide it by the smallest )
⇒
7.69
7.62
=
1.01
≅
1
It means that for 1 Hydrogen, you have 1 Carbon each time.
Empirical formula
≡
C
H