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Chemistry 2011 WAEC Past Questions

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51

(a) A compound X reacts with excess HNO\(_{3(aq)}\) to give carbon (IV) oxide and another compound Y. A solution of Y reacts with NaOH\(_{(aq)}\) to form a white precipitate which is insoluble in excess NaOH\(_{(aq)}\). Identify X and Y.

(b) (i) Write a balanced equation to illustrate the reducing property of ammonia in its reaction with CuO.

(ii) Explain why it is not advisable to heat ammonium dioxonitrate (III) directly.

(iii) Give two uses nitrogen.

(c) Give the reason why (i) dilute H\(_{2}\)SO\(_{4}\) is not suitable for the preparation of CO\(_{2(g)}\) from CaCO\(_{3(s)}\) (ii) concentrated H\(_{2}\)SO\(_{4}\) cannot be used to dry ammonia gas.

(d) State two: (i) physical properties; (ii) chemical properties of metals.

(e) What is the oxidation number of: (i) chlorine in I. Cl\(_{2}\). II. ClO\(_{-(3)}\)

(ii) vanadium in V\(_{2}\)O\(_{5}\)

(f)(i) Explain the term half-life. (ii) Two radioactive elements, P and Q have half-life of 1200 seconds and 3600 seconds respectively.

I. Which of the elements is more stable? II. Give a reason for your answer.

View Answer & Discuss (1) WAEC 2011
52

(a)(i) Draw the energy profile diagram for the reaction; H\(_{2(g)}\) + I\(_{2(g)}\) \(\to\) 2Hl\(_{(g)}\); \(\Delta\)H = –13 KJ mol\(^{-1}\)

(ii) If the concentration of HI\(_{(g)}\) increases from 0.000 to 0.002 mol dm\(^{-3}\) in 80 seconds, what is the rate of t reaction?

 

(b)(i)Give one use of each of the following compounds: I. NaHCO\(_{3}\); II. CaSO\(_{4}\); III. CaCO\(_{3}\).

(ii) State a drying agent that can be used for each of the following gases: I. SO\(_{2}\); II. HCI; Ill. NH\(_{3}\)

 

(c)(i) Write an equation for the complete combustion of carbon in oxygen.

(ii) Calculate the number moles of carbon (IV) oxide produced from the complete combustion of 2.5 g of carbon. [ C = 12.0, O = 16]

(iii) Mention one use of I. carbon (II) oxide; II. carbon (IV) oxide.

 

(d) An industrial raw material has the following composition by mass:

Iron = 28.1%; Chlorine = 35.7%; Water cf crystallization = 36.2%.

Calculate the formula for the material. [H = 1.00, O = 16.0, CI = 35.5, Fe = 56.0]

 

(e) Give one example of a (i) metal that is liquid at room temperature,

(ii) non-metal that is liquid room temperature.
 

View Answer & Discuss WAEC 2011
53

(a) A colourless gas P was given off when dilute tetraoxosulphate (VI) acid was added to zinc salt Q. On bubbling the gas through lime water, a white precipitate R was formed. Identify P, Q and R.

(b) Name a suitable apparatus that could be used to perform each of the following activities in the laboratory

(i) storage of dilute silver trioxonitrate (V):

(ii) heating copper metal;

(iii) separation of a mixture of water and Kerosene. Give one reason for each of your answers in (b)

View Answer & Discuss (3) WAEC 2011
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54

Credit will be given for strict adherence to the instructions, for observations precisely record and for accurate inferences. All tests, observations and inferences must be clearly entered in your answer book in ink, at the time they are made.

C is a mixture of two salts. Carry out the following exercises on C. Record your observations and identify any gas(es) evolved. State the conclusion drawn from the result of each fest

(a) Put all of C into a boiling tube and add about 5cm\(^3\) of distilled water. Stir thoroughly and filter. Keep both the residue and the filtrate.

(b) To about 2 cm\(^3\) of the filtrate, add few drops of Pb(NO\(_3\))\(_{(aq)}\). Boil the mixture and then allow to cool.

(c)(i) Put the residue in a test tube and add dilute HNO\(_{3}\). Shake the mixture and divide the solution into two portions

(ii) to the first portion from (c)(i), add NaOH\(_{(aq)}\) in drops acid then in excess.

(iii) To the second portion from (c)(ii), add aqueous ammonia in drops and then in excess

View Answer & Discuss WAEC 2011
55

Burette readings (initial and final) must be given to two decimal places. Volume of pipefte used must also be recored but no account of expeririental procedure is required. All calculations must be done in your answer book.

A is 0.100 mol dm\(^{-3}\) solution of an acid. B is a solution of KOH containing 2.8 g per 500 cm'\(^3\)

(a) Put A into the burette and titrate it against 20.0 cm\(^3\) or 25.0 cm\(^3\)  portions of B using methyl orange as an indicator. Repeat the titration to obtain consistent titres. Tabulate your readings and calculate the average volume of A used.

(b) From your results and the information provided above, calculate the:

(i) number of moles of acid in the average titre;

(i) number of moles of KOH in the volume of B pipetted;

(ii) mole ratio of acid to base in the reaction. [H = 1.00, O = 16.0, K = 39.0]

View Answer & Discuss WAEC 2011
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