- (i) What is the structure of the atom as proposed by Rutherford?
(ii) Distinguish between the atomic number and the mass number of an element.
(iii) Explain briefly why the relative atomic mass of chlorine is not a whole number. [ 7 marks]
- (i) What is meant by first ionization energy?
(ii) List three properties of electrovalent compounds
(iii) Consider the following pairs of elements:
- 9F and 17CL;
- 12Mg and 20Ca.
Explain briefly why the elements in each pair have similar chemical properties. [7marks ]
- Explain briefly the following terms using an appropriate example in each case
- homologous series;
- heterolytic fission. [5 marks ]
- State the indicator(s) which could be used to determine the end-point of the following titrations:
- dilute hydrochloric acid against sodium hydroxide solution;
- dilute hydrochloric acid against ammonium hydroxide solution;
- ethanoic acid against sodium hydroxide solution. [3 marks ]
- A solid chloride E which sublimed on heating reacted with an alkali F to give a
choking gas G. G turned moist red litmus paper blue. Identify E,F and G. [3 marks]
In part (a) majority of the candidates could not draw the structure of atom proposed by
Rutherford.
Many candidates could distinguished between the atomic number and the mass number
of an element and they were able to explain why the relative number of chlorine is not a
whole number.
In part (b) most candidates could not well state what is meant by first ionization energy
In part (c) majority of the candidates were able to explain the term homologous series.
but almost all the candidates could not explain the term heterolytic fission.
The expected answers were:
1. (a) (i) The atom has small/tiny positively charged centre/nucleus with electrons surrounding the space around the centre.
(ii) Atomic number of an element is the number of protons/electrons in an atom of the element while mass number is the sum of the protons and neutrons in the atom of the element.
(iii) Chlorine atom is made up of a mixture of isotopes and the relative atomic mass of chlorine is the average of its isotopic masses
(b) (i) Is the (minimum) energy required to remove one mole of an electron from one
mole of gaseous atom (to form one mole gaseous charged ion)
(ii) - High melting/boiling point;
- Ability to conduct electricity in the molten state or in solution;
- Solid at room temperature;
- Soluble in water or polar solvents/insoluble in non-polar solvents.
(iii) Atoms of the elements in each pair have the same number of electrons in their
outer-most shell therefore similar chemical properties.
(c) (i) Is a family of organic compounds:
- where successive members differ by –CH2 of molar mass of 14;
- with similar chemical properties;
- which conform to the same general formula;
- which show gradation of physical properties;
- which have the same general method of preparation.
e.g alkanes, alkenes , alkanols.
(ii) Is a process in which a (covalent) bond is broken in such a way that the electron pair is completely transferred to one of the atoms (resulting in the formation of ions)
H ÷ CI → H+ + Cl-/ HCl ® H+ + Cl-
(d) (i) - Methyl orange/methyl red/phenolphthalein;
(ii) - Methyl orange/methyl red;
(iii) - Phenolphthalein.
(e) E - NH4Cl
F - NaOH, KOH, or Ca (OH)2, Li OH, CsOH, Ba(oH)2,
Mg(OH)2
G - NH3
