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Chemistry WAEC Past Questions

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1456

(a)(i) Draw a labelled diagram for the laboratory preparation of a dry sample of chlorine

(ii) Give one chemical test for chlorine.

 

(b) Write equations to represent the reaction of chlorine gas with: (i) iron (II) chloride solution;

(ii) potassium iodide solution;

(iii) hot concentrated sodium hydroxide solution.

 

(c) State what is observed on:

(i) bubbling hydrogen chloride gas into an solution of lead (II) trioxonitrate (V);

(ii) heating the mixture from (c)(i) above to boiling and aging it to cool.

(d) A solution of bismuth chloride was prepared by adding the oxychloride which is a white powder to concentrated hydrochloric acid. The following equilibrium was set up: BiOCI\(_{(s)}\) + 2HCI\(_{(aq)}\) \(\rightleftharpoons\) BiCl\(_{3(aq)}\) + H\(_2\)O\(_{(q)}\). State what would be observed if some water is added to the system. Explain your answer

View Answer & Discuss WAEC 1994
1457

(a)(i) What is meant by hydrocarbons?

(ii) A hydrocarbon consists of 92.3% carbon. If it's vapour density is 39, determine its molecular formula. (H = 1; C = 12)

 

(b)(i) Outline a suitable laboratory procedure for obtaining ethanol from cassava tubers

(ii) List two laboratory reagents used for oxidizing ethanol to ethanoic acid.

 

(c) What name is given to each of the following processes?:

(i) Conversion of alkanols to alkanoates;

(ii) Breakdown of proteins to amino acids;

(iii) Conversion of oils to fats

(iv) Alkaline hydrolysis of fats and oils.

View Answer & Discuss WAEC 1994
1458

(a)(i) Determine the maximum number of electrons that can occupy the principal energy level M of an atom.

(ii) Show the changes in the electronic structures of atoms of sodium and fluorine (\(^{23}_{11}\)Na: \(^{19}_{9}F\)) when they combine to form sodium fluoride.

(iii) State: three properties that sodium fluoride would have, based a-n the bond type present in the compound.

 

(b) Write equations to show  when:

(i) sodium metal burns in limited supply of oxygen;

(ii) water is added to the product in (b)(i) above

 

(c) Describe a suitable laboratory procedure for comparing the conductance of 1 mol dm\(^{-3}\) aqueous solutions of sodium hydroxide and ethanoic acid.

View Answer & Discuss WAEC 1994
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1459

(a) (i) Define heat of combustion.

(ii) What name is given to the container used for determining tne reaction?

 

(b) The heat of combustion of carbon in excess air is - 3935 kJ.

(i) Sketch an energy profile diagram for the reaction.

(ii) Calculate the heat change when 60 g of carbon undergoes complete combustion to produce carbon (IV) oxide. (C = 12)

(iii) Explain why the value of the heat of neutralization of strong acids by strong bases is constant.

 

(c) Give reason for the following:

(i) rusting of iron is regarded as a slow combustion process;

(ii) iron filings rust much more faster than iron nails when exposed to the same atmospheric condition;

(iii) iron is better protected from corrosion by plating it with.zinc than with tin

View Answer & Discuss WAEC 1994
1460

Classify each of the following as physical change or a chemical change:

(a) fractional distillation of liquefied air;

(b) cracking of petroleum fractions;

(c) conversion of rhombic sulphur to monoclinic sulphur;

(d) chromatographic separation of chlorophyll.

View Answer & Discuss WAEC 1993
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