2017 - JAMB Chemistry Past Questions and Answers - page 2
11
For a general equation of the nature xP + yQ → mR + nS, the expression for the equilibrium constant is
A
k [P]x [Q]y
B
\(\frac{[P]^x [Q]^y}{[R]^m [S]^n}\)
C
\(\frac{[R]^m [S]^n}{[P]^x [Q]^y}\)
D
\(\frac{m[R] n[S]}{x[P] y[Q] }\)
correct option: c
Expression for equilibrium constant
k = \(\frac{\text{concentration of product}}{\text{concentration of reactant}}\)
Users' Answers & Commentsk = \(\frac{\text{concentration of product}}{\text{concentration of reactant}}\)
12
A given mass of gas occupies 2dm3 at 300k. At what temperature will its volume be doubled, keeping the pressure constant?
A
400k
B
480k
C
550k
D
600k
correct option: d
At constant pressure connotes Charle's law
\(\frac{V_1}{T_1}\) = \(\frac{V_2}{T_2}\)
\(\frac{2dm^3}{300k}\) = 2 x \(\frac{2dm^3}{T_2}\)
T2= 600k
Users' Answers & Comments\(\frac{V_1}{T_1}\) = \(\frac{V_2}{T_2}\)
\(\frac{2dm^3}{300k}\) = 2 x \(\frac{2dm^3}{T_2}\)
T2= 600k
14
An isomer of C5H12 is
A
2–ethyl butane
B
butane
C
2–methyl butane
D
2–methyl propane
correct option: c
C5H12 has 5 carbons acid 12 hydrogens.
2–methyl butane
No of carbon=5
No of hydrogen=12
Users' Answers & Comments2–methyl butane
No of carbon=5
No of hydrogen=12
15
When few drops of concentrated trioxonitrate(V) acid is added to an unknown sample and wanned an intense yellow colouration is observed. The likely functional group present in the sample is
A
NH3—C—C=O
B
CHO
C
CO
D
CNH2
correct option: a
Xanthopreitic test for the presence of protein, when conc nitric acid is added to the drop, an intense yellow colouration is observed.
It contains all the functional group of protein which includes the amino, alkanol and the carboxylic group. Adding few drops of conc HNO3 to a protein, gives an intense yellow colouration.
It is called Xanthopreitic test.
Users' Answers & CommentsIt contains all the functional group of protein which includes the amino, alkanol and the carboxylic group. Adding few drops of conc HNO3 to a protein, gives an intense yellow colouration.
It is called Xanthopreitic test.
16
A sample of orange juice is found to have a PH of 3.80. What is the concentration of the hydroxide ion in the juice?
A
1.6 \(\times\) 10-4
B
6.3 \(\times\) 10-11
C
6.3 \(\times\) 10-4
D
1.6 \(\times\) 10-11
correct option: b
PH = - Log[ H+ ]
PH + POH =14
POH = 14 - 3.8
POH = 10.2
POH = - Log[ OH- ]
10.2 = - Log[ OH- ]
10-10.2 = [ OH- ]
[ OH- ] = 6.3 x 10-11
Users' Answers & CommentsPH + POH =14
POH = 14 - 3.8
POH = 10.2
POH = - Log[ OH- ]
10.2 = - Log[ OH- ]
10-10.2 = [ OH- ]
[ OH- ] = 6.3 x 10-11
17
Incomplete oxidation of ethanol yields
A
CH3COOH
B
CH3COCH3
C
CH3CH2OCH2CH3
D
CH2CHO
correct option: d
C2H5OH → CH3CHO → CH3COOH
Ethanol.....oxidation Ethanal........Ethanoic Acid
Primary alcohol oxidises to aldehyde and later to carboxylic acid.
Secondary alcohol oxidises to ketones.
Ethanol is an example of primary alcohol and primary alcohol can be oxidised to aldehyde and carboxylic acid. Wherein, incomplete oxidation of primary alcohol yields aldehyde also known as alkaline while complete oxidation of primary alcohol yields carboxylic acid.
Users' Answers & CommentsEthanol.....oxidation Ethanal........Ethanoic Acid
Primary alcohol oxidises to aldehyde and later to carboxylic acid.
Secondary alcohol oxidises to ketones.
Ethanol is an example of primary alcohol and primary alcohol can be oxidised to aldehyde and carboxylic acid. Wherein, incomplete oxidation of primary alcohol yields aldehyde also known as alkaline while complete oxidation of primary alcohol yields carboxylic acid.
18
The salt formed from a weak acid and a strong base hydrolyzes in water to form
A
A saturated solution
B
an acidic solution
C
a buffer solution
D
an alkaline solution
correct option: d
This is a solution formed from the hydrolyses of an alkali in water.
Users' Answers & Comments19
The ideal gas laws and equations are true for all gases at
A
low pressures and lower temperatures
B
low temperatures and high pressures
C
high pressures and high temperatures
D
low pressure and high temperatures
correct option: d
At high temperature and low pressure, the vanderwaal equation is reduced to ideal gas equation.
i.e, [P + \(\frac{a}{v^2}\)] [v - b] = RT is reduced to PV = nRT
Generally, a gas behaves more like an ideal gas at higher temperature and lower pressure as the potential energy due to intermolecular forces, it becomes less significant compared with the particles kinetic energy and the size of the molecules, then it becomes less significant compared to the empty space between them.
Users' Answers & Commentsi.e, [P + \(\frac{a}{v^2}\)] [v - b] = RT is reduced to PV = nRT
Generally, a gas behaves more like an ideal gas at higher temperature and lower pressure as the potential energy due to intermolecular forces, it becomes less significant compared with the particles kinetic energy and the size of the molecules, then it becomes less significant compared to the empty space between them.
20
When ΔH is negative, a reaction is said to be
A
endothermic
B
exothermic
C
reversible
D
ionic
correct option: b
When ΔH is negative, heat is liberated to the surrounding and it connotes an exothermic reaction.
ΔH = −ve
Users' Answers & CommentsΔH = −ve