Chemistry Past Questions

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3996

Credit will be given for strict adherence to instructions, for observations precisely recorded, 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 and D are samples of two simple salts. Carry out the following exercises on them. Record your observations and identify any gases evolved. State the conclusion you draw from the result of each test.

(a) Put all of C in a test tube and heat strongly for about 3 to 5 minutes. Allow the residue to cool.

(b) Add about 5cm\(^3\) of distilled water to the residue from (a) above. Shake and test with litmus paper. 

 

 

 

View Answer & Discuss WAEC 1996
3997

 All your burette readings (initial and final), as well as the size of your pipette, must be recorded but no account of experimental procedure is required. All calculations must be done in your answer book.

A is a solution of tetraoxosulphate (VI) acid. B is a solution containing 1.4g of potassium hydroxide per 250cm\(^3\)

(a) Put A into burette and titrate with 20.0cm\(^3\) or 25.0cm\(^3\) portions of B using methyl orange or screened methyl orange as indicator. Record the volume of your pipette. Tabulate your burette readings and calculate the average volume of A used.

 

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

(i) concentration of B in mol.dm\(^{-3}\)

(ii) concentration of A in mol dm\(^{-3}\)

(iii) number of hydrogen ions in 1.0dm\(^{-3}\) of A. The equation for the reaction is: H\(_2\)SO\(_4\) + 2KOH \(\to\) K\(-2\)SO\(_4\) + 2H\(_2\)O. [H= 1, O = 16; K = 39. Avogadro constant = 6.0 x 10\(^{23}\)]

 

(c) State whether the pH of the following would be equal to 7, greater than 7 or less than 7

(i) Solution A:

(ii) Titration mixture of A and B before the endpoint

 

View Answer & Discuss WAEC 1996
3998

(a) Use the following reaction scheme to answer Questions;(i) - (iii) below;

Open Photo

(i) Give one suitable procedure for carrying out each of reactions 1, 2, and 3 separately in the laboratory

(ii) State the gases produced along with lead (lI) Oxide in reaction 1.

(iii) What is the colour of lead (II) tetraoxosulphate (VI)?

 

(b) When a drop of concentrated trioxonitrate (V) acid was added to potassium iodide solution, a violet-colored gas was evolved?

(i) What is the name of the gas evolved?

(ii) State the functions of concentrated trioxonitrate (V) acid in the reaction.

(iii) What would be observed if starch solution were added to the reaction mixture?

 

 

View Answer & Discuss WAEC 1995
3999

Credit will be given for strict adherence to instructions, for observations precisely recorded, 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 simple salts. Carry out the following exercises on C. Record your observations and identify any gases evolved. State the conclusion you draw from the result

(a)(i) Put all C in a boiling tube or beaker and add about 10cm\(^{3}\) of distilled water Stir the mixture thoroughly and tilter Keep both the residue and the filtrate

(ii) Test the filtrate with litmus paper.

 

(b) Divide the filtrate of two portions

(i) To the first portion of the filtrate. add about 2cm\(^3\) of dilute trioxonitrate (v) acid and then silver trioxonitrate (v) solution

(ii) To the second portion of the filtrate, add sodium hydroxide solution in drops until it is in excess.

 

(c) Put half of the residue in a test tube and heat strongly. Allow to cool

 

(d)(i) Put the remaining half of the residue in a test tube and add about 2cm\(^3\) of dilute hydrochloric acid.

(ii) To the resulting solution from (d(i)) above, add aqueous ammonia in drops until it is in excess.

 

 

View Answer & Discuss WAEC 1995
4000

 All your burette readings (initial and final), as well as the size of your pipette, must be recorded but no account of experimental procedure is required. All calculations must be done in your answer book.

A is a solution containing 6.3g dm\(^{-3}\) of impure ethanoic acid. B is 0.10mol. dm\(^{-3}\) sodium hydroxide sodium hydroxide solution.

(a) Put A into the burette and titrate with 20.0cm\(^3\) or 25.0cm\(^3\) portions of B using phenolphthalein as indicator. Record the volume of your pipette Record the volume of your pipette. Tabulate your burette readings and calculate the volume of A used.

(b) From your result and the information provided, calculate the

(i) concentration of solution A in mol.dm\(^{-3}\) 

(ii) Concentration of solution A in dm\(^{-3}\) and hence the percentage purity of the ethanoic acid,

(iii) Volume of solution A that would neutralize a solution containing 0.005 mole of sodium hydroxide. The equation for the reaction is;

H\(_2\)C\(_2\)O\(_{4(aq)}\) + 2NaOH\(_{(aq)}\) \(\to\) Na\(_2\)C\(_2\)O\(_{(aq)}\) + 2H\(_2\)O\(_{(l)}\) [H = 1; C = 12. O = 16]

(c)(i) What would be the colour of methylorange indicator in solution B?

(ii) Give the reason why methylorange is not a suitable indicator for titration. 

 

View Answer & Discuss WAEC 1995