Chemistry Past Questions

Change Subject Ask Question Check Syllabus Download App My Bookmarks

3976

State what you would see on;

(i) bubbling SO\(_2\) into acidified KMnO\(_4\) solution

(ii) mixing zinc dust with CuSO\(_4\) solution

(iii) adding concentrated HNO\(_3\) to freshly prepared FeSO\(_4\) solution.

(b) List two substances in case which, if added to dilute H\(_2\)SO\(_4\), would give you

(i) H\(_{2(g)}\)

(ii) ZnSO\(_{4(aq)}\)

 

(c)

Open Photo

The diagram labelled I to IV below illustrate different laboratory set-ups used in the separation of mixtures.

(i) Name the separation technique illustrated by each diagram

(ii) Which of the set-ups is used for concentrating dilute salt solutions, for the purpose of crystallization?

(iii) Which of the set-ups is used in obtaining clear water from muddy water?

(iv) Mention the set-up you would use to separate a polar solvent from a non-polar solvent

(v) State the modification you would make to the set-up labelled IV in order to use it for separating a mixture of NaCl and NH\(_4\)CI

View Answer & Discuss WAEC 2003
3977

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

A is 0.125 mol dm\(^3\) H\(_2\)SO\(_4\). B is a solution containing X g dm\(^{-3}\) of NaOH.

(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 indicator. Record the volume of your pipette. Tabulate your burette readings and calculate the average volume of A used. The equation for the reaction involved in the titration is H\(_2\)SO\(_4\) +2NaOH\(_{(aq)}\) \(\to\) Na\(_2\)SO\(_4\) + 2H\(_2\)O\(_{(l)}\)

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

(i) amount of H\(_2\)SO\(_4\) in the average volume of A used

(ii) Concentration of B in mol dm\(^{-3}\)

(iii) value of X.

[H = 1: O = 16; Na = 23]

 

(c) Describe briefly a suitable laboratory procedure for obtaining pure water from the titration mixture. (No diagram is required)

 

View Answer & Discuss WAEC 2002
3978

Credit will be given for strict adherence to the 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 i.itne time they are made.

C is a sample of copper (II) tetraoxosulphate (VI) crystals. Carry out the following exercises on C. Record your observations and identify any gases evolved. State the conclusion you draw from the result of each test.

(a) Put half of C in a test tube and heat strongly

(b) Make solution of about 10 cm\(^{-3}\) with the sécond half of C and divide it into three portions

(i) To the first portion, add Sodium hydroxide solution in drops and then in excess. Heat the mixture

(ii) To the second portion, add aqueous ammonia in drops and then in excess followed by few drops of moderately concentrated HCI.

(iii) To the third portion, add all the zinc dust provided and stir thoroughly until there is a visible change.

View Answer & Discuss WAEC 2002
3979

(a) Suggest how the following liquid reagents can be suitably stored in the laboratory   

(i) X which fumes in moist air; 

(ii) Y which is slowly decomposed by sunlight in ordinary reagent bottles.

 

(b) State what is observed when aqueous ammonia is added to:

(i) litmus paper;

(ii) Pb(NO\(_3\))\(_2\) solution in drops until in excess

(iii) freshly precipitated AgCI in excess.

 

(c) A salt sample was suspected to be either Na\(_2\)CO\(_2\) or NaHCO\(_3\). A student who was required to identify it tested a portion for solubility in water and then for effect on litmus paper.

(i) What was observed in each case?

(ii) Give the reason why the student's procedure was unsuitable

(iii) Describe briefly how you would have identified the salt.

 

View Answer & Discuss WAEC 2002
3980

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

A is mol dm HCI. B is a solution containing 15.0 g dm of a mixture of NaCl and KHCO\(_3\).

(a) Put A burette and titrate it against 20.0cm\(^3\) or 25.0cm\(^3\) portions of B using methyl orange as indicator. Record the volume of your pipette. Tabulate your burette readings and calculate the average volume of A used. The equation for the reaction involved in the titration is: HCl\(_{aq}\) + KHCO\(_{3(aq)}\) \(\to\) KCl\(_{(aq)}\) +CO\(_{2(g)}\) 

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

(i) concentration of KHCO\(_3\), in mol dm\(^{-3}\) in B;

(ii) mass of KHCO\(_3\), in g dm\(^{-3}\) in B

(ii) Percentage by mass of KHCO\(_{3}\) in the mixture, [H=1; C = 12; O = 16; K = 39]

(iv) mass of NaCl in the mixture.

 

View Answer & Discuss WAEC 2001