2019 - JAMB Chemistry Past Questions and Answers - page 3

21

When ammonia and hydrogen ion bond together to form ammonium ion, the bond formed is called

A
electrovalent bond
B
co-ordinate bond
C
ionic bond
D
covalent bond
correct option: b

When ammonia and hydrogen ion go into bonding, they form ammonium ion by combining with a dative/coordinate covalent bond.

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22

Which of the following represents the kind of bonding present in ammonium chloride?

A
ionic only
B
covalent only
C
ionic and dative covalent
D
dative covalent
correct option: c
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23

Consider the reaction
A\(_{(s)}\) + 2B\(_{(g)}\) → 2C\(_{(aq)}\) + D\(_{(g)}\)
What will be the effect of a decrease in pressure on the reaction?

A
the equilibrium will shift
B
rate of forward reaction will increase
C
rate of backward reaction will increase
D
rates of forward and backward reaction are not affected
correct option: b

Given: The equation below
A\(_{(s)}\) + 2B\(_{(g)}\) → 2C\(_{(aq)}\) + D\(_{(g)}\)
Since we have a higher number of moles of gaseous species on the LHS, i.e 2, a decrease in pressure will favor the forward reaction.

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24

For the general equation of the nature
xP + yQ ⇌ mR + nS, the expression for the equilibrium constant is

A
k[P]\(^x\)[Q]\(^y\)
B
\(\frac{m[R][S]}{x[P]y[Q]}\)
C
\(\frac{[P]^x[Q]^y}{[R]^m[S]^n}\)
D
\(\frac{[R]^m[S]^n}{[P]^x[Q]^y}\)
correct option: d

Given:
xP + yQ ⇌ mR + nS
Let us assume they are all in aqueous solution

k = \(\frac{[R]^m[S]^n}{[P]^x[Q]^y}\)

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25

Which of the following reactions is an oxidation process?

A
2H\(^+\) + 2e\(^-\) \(\to\) H\(_2\)
B
2O\(^{2-}\) + 4e\(^-\) \(\to\) O\(_2\)
C
OCl\(^-\) + H\(_2\)O + 2e\(^-\) \(\to\) 2OH\(^-\) + Cl\(^-\)
D
Cl + e\(^-\) \(\to\) Cl\(^-\)
correct option: b
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26

If acidified Potassium Dichromate(VI) (K\(_2\)Cr\(_2\)O\(_7\)) acts as oxidizing agent, color changes from

A
yellow to green
B
orange to green
C
yellow to red
D
orange to red
correct option: b

Potassium dichromate is an oxidising agent in organic chemistry. It is used to oxidize alcohols.

In an aqueous solution the color change exhibited can be used to test for distinguishing aldehydes from ketones. Aldehydes reduce dichromate from the +6 to the +3 oxidation state, changing color from orange to green. This color change arises because the aldehyde can be oxidized to the corresponding carboxylic acid.

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27

The heat of formation of ethene, C\(_2\)H\(_4\) is 50 kJmol\(^{-1}\), and that of ethane, C\(_2\)H\(_6\) is -82kJmol\(^{-1}\). Calculate the heat evolved in the process:

C\(_2\)H\(_4\) + H\(_2\) \(\to\) C\(_2\)H\(_6\)

A
-122kJ
B
-132kJ
C
-88kJ
D
-60kJ
correct option: b
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28

Which of the following statements about catalyst is false?

A
biological catalysts are called enzymes
B
catalyst do not appear in the balanced equation
C
catalyst reduce the activation energy for a reaction
D
catalysts do not alter the mechanism of the reaction and never appear in the rate low
correct option: d
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29

Which of the following does not support the fact that air is a mixture?

A
the constituents of air are in a fixed proportion by mass
B
it cannot be represented with a chemical formula
C
the constituents of air can be separated by physical by physical means
D
none of the above
correct option: a
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30

What technique is suitable for separating a binary solution of potassium chloride and potassium trioxochlorate (V)?

A
Fractional crystallization
B
Fractional distillation
C
Filtration
D
Evaporation
correct option: a
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