Determine the molecular formula of an ox | Class 11 Chemistry Chapter Some Basic Concepts of Chemistry, Some Basic Concepts of Chemistry NCERT Solutions

Question:

Determine the molecular formula of an oxide of iron in which the mass per cent of iron and oxygen are 69.9 and 30.1 respectively. Given that the molar mass of the oxide is 159.69 g mol^–1.

Answer:

From the available data Percentage of iron = 69.9

Percentage of oxygen= 30.1

Total percentage of iron & oxygen= 69.9+30.1= 100%

Step 1 calculation of simplest whole number ratios of the elements

Element	Percentage	Atomic mass	Atomic ratio	Simplest ratio	Simplest whole no ratio
Fe	69.9	55.84	69.9/55.84=1.25	1.25= 1	2
O	30.1	16	30.1/16 = 1.88	1.88=1.5	3

Step 2 Writing the empirical formula of the compound

The empirical formula of the compound = Fe₂ O₃

Step 3 determination of molecular formula of the compound

Empirical formula mass = 2 X69.9 + 3 X16=187.8 amu

Molecular mass of oxide= 159.69g/mol(given)

Now we know molecular formula = n x Empirical formula

And n= molecular mass / empirical formula mass= 159.69/187.8 = 0.85 = approx 1

Therefore molecular formula = n x empirical formula

=1 x(Fe₂O₃) = Fe₂O₃

The molecular formula of the oxide is Fe₂O₃

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Comments

Siyara bhatt
2019-07-13 00:43:38

Thank you so much!

Siyara bhatt
2019-07-13 00:15:57

Thank you so much!

Prachi
2019-07-03 20:33:59

Thanks... ð

Khusboo Chawla
2019-06-16 11:56:48

Thank you everyone ððð

Shine
2019-06-10 20:04:18

Not clear on empherical formula

Hari
2019-04-29 23:17:10

Empirical formula not clear

Saba sindhi
2019-01-18 19:02:20

New sem 2 text solution

Akshatha
2018-11-30 23:05:17

Thanks

Tanaya Satange
2018-11-29 08:45:23

Respected teacher, You have taken the percentage of iron instead of the molar mass of iron while calculating the Empirical Formula mass.Thank you for making available such detailed answers to us.

Aynal Hoque
2018-10-22 11:35:43

In NCERT the molecular mass of oxide is not given....that's why I was in trouble to find the answer...thank's for this information..

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Welcome to the NCERT Solutions for Class 11 Chemistry - Chapter . This page offers a step-by-step solution to the specific question from Excercise 1 , Question 8: Determine the molecular formula of an oxide of iron in which the mass per cent of iron and oxygen ar....

Determine the molecular formula of an ox | Class 11 Chemistry Chapter Some Basic Concepts of Chemistry, Some Basic Concepts of Chemistry NCERT Solutions

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