2018 - JAMB Chemistry Past Questions and Answers - page 1

1

Which of the following metals cannot replace hydrogen from water or steam?

A
Sodium
B
Magnesium
C
Iron
D
Calcium
correct option: d

Metals above hydrogen in the activity series can displace or replace hydrogen present in water (H2O) example of such metals are Ca, K, Na etc. But the metals below hydrogen in the activity series cannot replace hydrogen in the activity series example of such metals are Cu Hg.

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2

Elements P, Q, R, S have 6, 11, 15, 17 electrons respectively, therefore,

A
P will form an electrovalent bond with R
B
Q will form a covalent bond with S
C
R will form an electrovalent bond with S
D
Q will form an electrovalent bond with S
correct option: d

P 6 = 2, 4

  Q 11 = 2, 8, 1

  R 15 = 2, 8, 5

  S 17 = 2, 8, 7

  Given the above is the electronic arrangement of PQRS elements, Q will form an electrovalent bond with S. Without argument, D is the answer because electrovalency involves the transfer of electron. Already, Q is 11 with electronic configuration of 2, 8, 1, i.e. having 1 valence electron which is ready to be lost by the atom of element Q, also, S is 17, with electronic configuration of 2, 8, 7. There the 7 valence electron of S attracts that only 1 electron to attain a stable octet structure.

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3

During the electrolysis of copper II sulphate between platinum electrodes, if litmus solution is added to the anode compartment

A
the litmus turns blue but no gas is evolved
B
the litmus turns blue and oxygen is evolved
C
the litmus turns blue and hydrogen is evolved
D
the litmus turns red and oxygen is evolved
correct option: d
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4

The derivative of benzene that can be used in making explosives is

A
aniline
B
xylene
C
phenol
D
toluene
correct option: c
Ethyl benzene is used to manufacture styrene, which is used in the production of latex, synthetic rubber and polystyrene, which is used mainly in food packaging. Phenol and its derivatives are used to make aspirin, antiseptics, explosives, plastics, and dyes used in textiles and food.
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5

In electrovalency, the oxidation number of the participating metal is always

A
decreasing
B
increasing
C
constant
D
neutral
correct option: c

In electro-valency the oxidation number of the participating metal remains constant

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6

The ionic radii of metals are usually

A
greater than their atomic radii
B
unaffected by the charge on the ion
C
the same as their atomic radii
D
less than their atomic radii
correct option: d
Ionic Radius vs. Atomic Radius Metals - the atomic radius of a metal is generally larger than the ionic radius of the same element. Why? Generally, metals loose electrons to achieve the octet. This creates a larger positive charge in the nucleus than the negative charge in the electron cloud, causing the electron cloud to be drawn a little closer to the nucleus as an ion. Non-metals - the atomic radius of a non-metal is generally smaller than the ionic radius of the same element. Why? Generally, non-metals loose electrons to achieve the octet. This creates a larger negative charge in the electron cloud than positive charge in the nucleus, causing the electron cloud to 'puff out' a little bit as an ion. Cations (or anions) of different elements are said to be **isoelectronic** if they both have the same electronic configuration e.g. K+ and Ca 2+ For isoelectronic cations, the more positive the ionic charge, the smaller the ionic radius. For isoelectronic anions, the more negative the ionic charge, the larger the ionic radius. ubc.ca
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7

Calculate the percentage composition of oxygen in calcium trioxocarbonate(IV) [Ca=40, C=12, O=16]

A
16
B
48
C
40
D
12
correct option: b

Calcium trioxocarbonate (IV) = CaCO\(_3\)

  Percentage of Oxygen = \(\frac{\text{Molar mass of 3O}}{\text{Molar mass of} CaCO_3}\) × 100%

  Percentage of Oxygen = \(\frac{(3 \times 16)}{(40 + 12 + 48)}\)  x 100%

  Percentage of Oxygen = \(\frac{48}{100}\) x 100%

  Percentage of Oxygen = 48%

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8

Which of these alloys contains copper?

A
solder
B
steel
C
permallory
D
bronze
correct option: d

Bronze is an alloy consisting primarily of copper, commonly with about 12% tin and often with the addition of other metals (such as aluminium, manganese, nickel or zinc) and sometimes non-metals or metalloids such as arsenic, phosphorus or silicon.

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9

If the molecular mass of tetraoxosulphate (VI) acid is 98, calculate its vapour density.

A
196
B
49
C
106
D
82
correct option: b

Molecular mass = Vapour Density x 2

  Vapour Density = \(\frac{\text{Molecular Mass}}{2}\)

  Where Molecular mass = 98g/mol

  Vapour Density = \(\frac{98}{2}\)

  Vapour Density = 49g/mol

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10

Sieving is a technique used to separate mixtures containing solid particles of

A
small sizes
B
large sizes
C
different sizes
D
the same size
correct option: c
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