2018 - JAMB Chemistry Past Questions and Answers - page 1

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.

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.

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.

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

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

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%

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.

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