Calculate the molecular mass of the following:
(i) H2O
(ii) CO2
(iii) CH4
Molecules are made up of atoms & are quite small, therefore the actual mass of a molecule cannot be detrmined.It is expressed as the relative mass.C-12 isotope is used to express the relative molecular masses of substances.Thus molecular mass of a substance may be defined as: the average relative mass of its molecule as compared to the mass of carbon atom taken as 12 amu.
(i) H2O:
The molecular mass of water, H2O
= (2 × Atomic mass of hydrogen) + (1 × Atomic mass of oxygen)
= [2(1.0084) + 1(16.00 u)]
= 2.016 u + 16.00 u
= 18.016
= 18.02 u
(ii) CO2:
The molecular mass of carbon dioxide, CO2
= (1 × Atomic mass of carbon) + (2 × Atomic mass of oxygen)
= [1(12.011 u) + 2 (16.00 u)]
= 12.011 u + 32.00 u
= 44.01 u
(iii) CH4:
The molecular mass of methane, CH4
= (1 × Atomic mass of carbon) + (4 × Atomic mass of hydrogen)
= [1(12.011 u) + 4 (1.008 u)]
= 12.011 u + 4.032 u
= 16.043 u
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Welcome to the NCERT Solutions for Class 12 Chemistry - Chapter . This page offers a step-by-step solution to the specific question from Excercise 2 , Question 13: Why is zinc not extracted from zinc oxide through reduction using CO?....
(iv) 
Comments
Very creative anawer
Very impressive answer. This helped me a lot. Thank you
For those who can't understand, please take a look at the ellingham's graph. First, the equation could be split into 2 equations: 1) 2ZnO --> 2Zn + O2. And 2) 2CO + O2 --> 2CO2. Now take a look on the ellingham's graph. See that the graph of eq(1) is lowe than graph of eq (2) which means that CO can't reduce ZnO to Zn, therefore, CO is not used.
Cant understand pls elaborate
Thanx .this answer is more impressive