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.

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

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