Question

1.116 A hydrocarbon contains 85.7% carbon. If 42 mg of
the compound contain 3.01 x 102° molecules, find
the molecular formula of the compound.
Tans. CfH12

Answer 1

Explanation:

Mass of Compound = 42 mg = 42 x 10-3 g

6.022 x 1023 molecules of compound = 1 mole

3.01 x 1020 molecules = (3.01 x 1020 ) / (6.022 x 1023 ) = 0.5 x 10-3 moles of compound

Molar mass of the compound = Mass /No. of moles = 42 x 10-3 g / 0.5 x 10-3 = 84 g/mol

Mass of Carbon in 1 mole of Compound = 85.7/100 x 84 g/mol = 71.98 = 72 g/ mol of C

Mass of H in 1 mole = (14.3/100) x 84 = 12.012g /mol of H

No. of C atoms = 72 / 12 = 6

No. of H atoms = 12.012 /1 = 12

Therefore the formula of the compound is C6H12.

$\huge \sf{\green{\fbox{\red{\fbox{\green{\fbox{\red{PLS FOLLOW}}}}}}}}$

Answer 2

Answer:

So the molecular formula of the hydricarbon compund is C6H12.

Explanation:

Answer

85.7 % carbon ⇒100−85.7=14.3 % Hydrogen

gram molecular weight= 6.023×10

23

⇒42mg=3.018×10

20

⇒84mg=6.02×10

20

& 84g=6.02×10

23

∴85.7 %=

100

85.7

×84=72g

1 mole of C=12g

6 moles of C=12×6=72g

∴ There are 6 carbons in each molecule

84−72=12g of H=12H atoms in each molecule

∴ Molecular formula= C

6

H

12