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
In a pseudo first order hydrolysis of ester in water, the following results were obtained:
| t/s | 0 | 30 | 60 | 90 |
|
[Ester]mol L - 1 |
0.55 | 0.31 | 0.17 | 0.085 |
(i) Calculate the average rate of reaction between the time interval 30 to 60 seconds.
(ii) Calculate the pseudo first order rate constant for the hydrolysis of ester.
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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 14: The half-life for radioactive decay of 14C is 5730 years. An archaeological artifact containing wood....
Comments
My answer is 1919
How 0.693 come
The answer will be 1910 yrs T=1/KÃln(A°/A) Also, 1/K=t(1/2)/ln2 So, T=[t(1/2)/ln2]Ãln(A°/A) T= 5730yrs Ã(log5-log4/log3)
All radioactive decay are of 1st order reaction. So zero order can't be taken.
What if zero order?
radioactive decay is first order reaction & half-life of first order =0.693/k first you will find the value of k then put in formule and use log value of log100/80=log5/4=log5-log4
Hii how this answer came out to be 1845