Chemistry Past Questions

4011

A is a solution containing 0.50 mole of barium chloride per dm$$^3$$. Solution B contains 1.0 mole of tricxocarbonate (IV) salt per dm$$^3$$

(a) State what would be observed and give the confirmatory test for any gases evolved if the following tests were performed

(i) mixing 2cm$$^3$$ each of solutions A and B in a test tube

(ii) adding excess dilute hydrochloric acid to the mixture from (a)(i) above

(b) 10cm$$^3$$ of solution A were measured into each of seven boiling tubes of uniform bore and various quantities of solution B were added respectively to the boiling tubes, The tubes were immersed in hot water. After the reaction, the height of the product in each of the tubes was measured. The results were as tabulated below.

 Test tube I II III IV V VI VII Volume of sodium B added (cm$$^3$$) 2.0 3.0 4.0 5.0 6.0 7.0 8.0 Height of the product (to the nearest m) 12 18 24 30 30 30 30

(i) Plot a graph of the height of the product against the volume of solution B added to each test tube. Explain the shape of the graph

(ii) Calculate the amount (in mole) of the trioxocarbonate (IV) salt contained in the volume of solution B added to tube lV

(iii) Calculate the amount (in mole) of barium chloride contained in 10cm$$^3$$ of solution A. Hence, determine the mole ratio of barium chloride and the trioxocarbonate (IV) Salt in the reaction

WAEC 1991
4012

C is a mixture of an organic and an inorganic salt. The test recorded in the table below were performed as indicated,

(a)Copy and complete the table as appropriate.

 Test Observation Inference (i) C + water mixed thoroughly and filtered Partially soluble, colourless filtrate, white residue (ii) Portion of filtrate from (i) + NH$$_{3(aq)}$$ in drops, then in excess White precipitate which dissolves in excess to give a colourless solution (iii) Portion of filtrate from (i) + NH$$_3$$ in drops, then in excess White precipitate insoluble in excess (iv) Portion of filtrate from (i) + conc. HCl + heat White precipitate which dissolves on warming and reappears on cooling (v) Portion of filtrate from (i) + conc. H$$_2$$SO$$_4$$ + gentle warming Brown fumes produced on warming (vi) Residue from (i) + iodine solution Blue-black colouration (vii) Residue from (i) + Fehling's solution + heat (vii) Residue from (i) + dil HCl  solution + heat + Fehling's solution

(b) From the information provided and your inference, identify the compounds of C

(c) Describe the action of heat on a solid sample of the inorganic component  Write an equation for the reaction.

(d) State what would be observed if an aqueous suspension of the organic component were heated to boiling

WAEC 1991
4013

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

Xg of pure potassium trioxocarbonate (IV) was treated with 1dm$$^3$$ of 0. 25M tetraoxosulphate (VI) acid to obtain solution A which contains excess acid. B is a solution containing 2.8g of potassium hydroxIde per 250cm$$^3$$ solution.

(a) Put A into the burette and titrate with 20cm$$^3$$ or 25cm$$^3$$ portions of B. using methyl orange as indicator. Record the volume of your pipette. Tabulate your burette readings and calculate the average volume of acid used.

(b) From your results and the information given. Calculate the;

(i) concentration of the excess acid in A in mol dm$$^3$$

(iii) value of X. The equation for the reaction between the excess acid the potassium hydroxide is H$$_2$$SO$$_4$$ + 2KOH $$\to$$ K$$_2$$SO$$_4$$ [H = 1. C = 12, O = 16. S = 32, K = 39]

WAEC 1990
4014

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 time they are made. Carry out the following exercises on sample C.

Record your observations and identify any gases evolved

(a) Put all of C into a test tube and add about 5cm$$^3$$ of water. Shake the mixture and filter. Keep both the residue and the filtrate

(b) Divide the filtrate into two portions;

(i)  To the first portion, add a few drops of dilute trioxonitrate (V) acid followed by about 1cm$$^3$$ of silver trioxonitrate (V) solution

(ii) Add excess aqueous ammonia to the mixture in (i) above

(iii) To the second portion, add about 2cm$$^3$$ of dilute sodium hydroxide solution and warm gently

(c) Add about 2cm$$^3$$ of dilute hydrochloric acid to the residue from (a) above and warm gently. Filter if necessary and divide the resulting solutio into two portions.

(i) To the first portion add dilute sodium hydroxide solution in drops until it is in excess

(ii) To the second portion, add aqueus ammonia in drops until it is in excess.

WAEC 1990
4015

(a)(i) Give one laboratory use of activated charcoal

(ii) A piece of phosphorus and some magnesium ribbon were burnt in two separate jars of oxygen. Water was then added to dissolve the product. State the action of litmus on each of the resulting solutions

(b) Give one chemical test to distinguish between CH$$_3$$CH$$_2$$OH and CH$$_3$$COOH.

(c) Describe how you would dilute accurately a solution containing 0.10 mole of the solute per dm$$^3$$ of solution to 0.010M.

WAEC 1990