Chemistry Past Questions And Answers
(a) Mention one oxide in each case, which
(i) used in bleaching
(ii) is a redish-brown gas
(iii) reacts with NaOH and also with HCI;
(iv) dissolves in water to give a solution with pH greater than 7;
(v) oxidizes hot, concentrated HCI to chlorine
(b)(i) State three methods that can be used to removo hardness in a sample of water that contains calcium hydrogentrioxocarbonate (IV).
(ii) Explain with the aid of appropriate equation, why it is not advisable to build a house with limestone in an environment polluted by sulphur (IV) oxide.
(c)(i) List two compounds of potassium which yield oxygen when heated strongly
(ii) Calculate the amount (in moles) of gas which occupies 250 cm\(^3\) at s.t.p. [1 mole of gas occupies 22.4 dm\(^3\) at s.t.p]
(iii) If 250 cm\(^3\) of a gas at s.t.p. is heated to 27°C at constant pressure, calculate its new volume.
(iv) Explain in terms of the collision theory what happens as a gas is heated at constant pressure.
View Discussion (0)WAEC 2003 THEORYWhich is most acidic oxide of the following?
- A) CO
- B) MnO
- C) CaO
- D) N2O
(a)(i) Define each of the following terms: I. normal salt. II. acid salt.
(ii) Tetraoxosulphate (VI) acid and sodium hydroxide react to produce salt and water. Write a balanced chemical equation fir the formation of: I. a normal salt; II. an acid salt.
(b)(i) Explain briefly the term acid-base indicator.
(ii) Copy and complete the following table.
Indicator | , Colour in acidic medium | , Colour in basic medium |
Methyl orange | ||
Phenolphthalein |
(iii) For each of the following titrations, state the most suitable indicator: I. strong acid against strong base; II. strong acid against weak base; iii. weak acid against strong base.
(c) Baking soda and hydrochloric acid react according to the following equation:
NaHCO\(_{3(aq)}\) + HCI\(_{(aq)}\) ---> NaCl\(_{(aq)}\) CO\(_{2(g)}\) + H\(_2\)O\(_{(l)}\). Calculate the mass of baking soda that would produce 10g of ccrbon (IV) oxide. [H = 1.00, C = 12.0, 0 = 16.0, Na = 23.0]
(d) Give a reason why a given mass of sodium hydroxide pellets cannot be used to prepare a standard solution.
NaHCO\(_3\) + HCI --> NaCI + CO\(_2\) + H\(_2\)O
84g NaHCO\(_3\) --> 44g CO\(_2\)
Xg --> 10g CO\(_2\)
Xg = \(\frac{84 \times 10}{44}\)
= 19.09g
= 19.1g.
(d) give a reason why a given mass of sodium hydroxide pellets cannot be used to prepare a standard solution: Sodium hydroxide absorbs water/deliquescent and absorbs carbon IV oxide from air/and this would make mass taken unreliable/add to its mass.
View Discussion (0)WAEC 2013 THEORYWhich of the following factors would not affect the solubility of a gas?
- A. Concentration
- B. Nature of solvent
- C. Pressure
- D. Temperature
Aluminium is used in the manufacture or aircraft because it
- A. Is hard and brittle
- B. Is light and resists corrosion
- C. Has high density and conducts electricity
- D. Is malleable and ductile
Terylene is synthesized from ethane- 1, 2-diol and benzene - 1, 4-dicarboxylic acid by?
- A. addition reaction
- B. condensation reaction
- C. elimination reaction
- D. substitution reaction
(a) Mention the chemical substance manufactured starting from each of the foirownc sets of materials:
(i) sugar and yeast;
(ii) ammonia, air and water;
(iii) vegetable oil and caustic alkali.
(b) State one air pollutant generated during the manufacture of fertilizers.
View Discussion (0)WAEC 1995 THEORYCH2S(g) + O2(g) → 2Cn + SO2(g) What is the change in the oxidation number of copper in the reaction?
- A) 0 to + 2
- B) 0 to + 1
- C) C + 1 to 0
- D) + 2 to + 1
Which of the following are mixtures? i, Petroleum ii, Rubber latex iii. Vulcanizer's solution iv, Carbon (II)sulphide
- A. i, ii and iii
- B. i, ii and iv
- C. i and ii only
- D. i and iv
(a)(i) What is the general formula for alkanoic acids?
(ii) State two chemical properties of ethanoic acid.
(b) Which of propene, butane and pentane
(i) will decolorize acidified KMnO\(_4\) solution?
(ii) can be easily polymerized?
(iii) is an isomer of methylpropane?
(iv) can be obtained from an alkanol by dehydration?
View Discussion (0)WAEC 1998 THEORY