KPK Board 12th class Chemistry Ch 24 Analytical Chemistry questions answers
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Malakand Board 12th classes short questions Answer
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Magnesium perchlorate is an excellent dehydrating agent used in the combustion analysis. It does not become sticky when exposed to air and the glass tube can easily be cleaned.
Solution:
mass of Acetic acid = 5gm
mass of H2O=3gm
mass of Co2 = 7.33gm
%age of elements =?
Empirical formula =?
Mass of CO2/mass of compx12/44x100o
C =7.33/5×12/44×100=39.7
%age of H2, = mass of H20/mass of compx2.02/18 x100
=3g/5×2.02/18×100
%age of H2 = 0.6×0.11×100 = 6.6%
%age of O2, = (100-%C+%H)
%age of O2, = 100-39.7 +6.6
%O2, = 53.7%
Moles of C = 39.7/12 = 3.30moles
Moles of H = 6.6/1.01 = 6.5
Moles of O2,=53.7/16=3.35
Molar Ratio
C : H : O
3.30/3.30: 6.5/3.30 :3.35/3.30
1 : 1.95 : 1.01
As 1.96 ͌ 2 So
С H O
1 2 1
So empirical formula acetic acid is CH2O
Solution:
%age of C = 88.17%
%age of H = 11.83%
Molar mass = 68.11g/mole
Empirical formula =?
Molecular formula =?
Moles of C – 88.17/12=7.34mole
Moles of H2, = 11.83/ 1.01=11.83
Molar Ratio =
C : H
7.34/7.34 : 11.83/7.34
1 : 1.61
Now multiply it with 5 to get simple ratio
Simple ratio
C : H
5 (1 : 1.6)
C5H8 empirical formula.
Now molecular formula if isoprene
Empirical formula mass = C5H8
= 60+8= 68g
n=M.mass 68/ E.F.mass= 68/68=1
M.Formula = nx Empirical formula
= 1xC5H8
M.formula = C5H8
This shows that both empirical and molecular formulas of isoprene’s are same
CH,
CH2 =CH-C=CH2
Modern methods of analysis are superior over classical methods because of the following reasons.
- Small amount of chemicals are required.
- Chemicals are not wasted in large amount.
- These methods are rapid and less time consuming.
- They give more accurate results.
- These methods are simple and do not involve much chemistry as compared to the classical methods.
(i) IR Function: The main function of IR spectroscopy is identification of different functional group present in an organic compound.
- ii) UV-Vis: The main function of UV-visible spectroscopy is to measure the conjugation of double bonds.
iii) NMR: The main function of NMR spectroscopy is to determine the number and kind of protons present in an organic compound.
- iv) Mass Spectroscopy: The main function of mass spectroscopy is to give informations about molecular mass of an organic compound.
Conclusion: All these four techniques helps the organic chemist to determined the structure of an organic compound.
Ans. Beer-Lambert’s Law state that the ”quantity of light absorbed by a substance dissolved in a fully transmitted solvent is directly proportional to the concentration of substrate and path length of light through the solution.
A=Elc
The quartz cuvets are transparent in the UV region while glass cuvets shows maximum absorbance in UV region. However they can be used in visible region where they are transparent.
