Question

calculate empricial formula of the compound which has the following composition carbon 80% hydrogen 20%. if the molecular mass is 30 calculate it's molecular formula
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Answer 1

Answer:

Ethane C2H6

Explanation:

Let the mass of unknown compound be 100 g.

Given that the compound contains 80% of carbon and 20% of hydrogen.

Therefore, weight of carbon in the compound =80g

weight of hydrogen in the compound =20g

Molecular weight of carbon =12g

Molecular weight of hydrogen =1g

∴ moles of carbon in the compound = 80÷12 =6.67

Moles of hydrogen in the compound = 20÷1 = 20

Ratio of no. of moles of carbon to no. of moles of hydrogen-

No. of moles of carbon : no. of moles of hydrogen =

6.67 : 20≈ 1:3

∴ 3 moles of hydrogen are present in the compound for 1 mole of carbon.

Hence, the empirical formula of the compound is CH3

empirical mass=15 g/mol

Molecular formula =(CH3 )n

whereas,

n= empirical mass ÷ molecular mass = 30÷15 =2

Thus, the molecular formula of the compoud is C2H6