### Chemistry Past Questions

3986

(a) List two gases in each case which;

(i) can be used to demonstrate the fountain experiment;

(ii) decolourize acidified potassium tetraoxomanganate (VII).

(b) State briefly how you would distinguish between

(i) crystals of PbCO$$_3$$ and Pb(NO$$_3$$) using heat;

(ii) solutions of NH$$_4$$CI and NaCl using litmus paper.

(c) Mention two changes that would be observed on adding moderately concentrated hydrochloric acid to iron filings

WAEC 1999
3987

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 inorganic compounds. 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 all of C into a beaker and add about 10cm$$^3$$ of distilled water. Stir thoroughly and filter. Keep both the residue and the filtrate

(b) Divide the filtrate into three portions.

(i) To the first portion, add sodium hydroxide solution in drops until ít is in excess.

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

(iii) To the third portion, add about 2cm$$^3$$ of barium chloride solution, followed dilute hydrochloric acid in excess.

(c) Put the residue in a test tube and add about 2cm$$^3$$ of dilute tetraoxosulphate (VI) acid. Shake the mixture and warm.

(i) Add aqueous ammonia in drops to the mixture from (c) (i) above until it is in excess.

WAEC 1999
3988

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

(a) Put A into the burette and titrate it against 20.0 cm$$^3$$ or 25.0 cm$$^3$$ portion 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 is 2NaOH$$_{(aq)}$$ + H$$_2$$X$$_{(aq)}$$ $$\to$$  2H$$_2$$O$$_{(l)}$$

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

(i) Concentration of solution B in mol dm$$^{-3}$$

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

(iii) molar mass of the acid H$$_2$$X. [H = 1, O = 16, Na = 23]

WAEC 1999
3989

(a) A soluble chloride X reacted with a liquid Y on heating, to give gas Z which turned moist blue litmus paper red and fumed in moist air.

(i) Identity Y and Z

(ii) Give one chemical test to confirm that X is a chloride

(b)(i) State one laboratory use of calcium chloride.

(ii) Name one laboratory technique suitable for separating a mixture of iron filings and ammonium chloride without applying heat.

(iii) State the action of solutions of the following salts on litmus respectively: K$$_2$$CO$$_3$$;  NaNO$$_3$$, AICl$$_3$$, (NH$$_4$$)$$_2$$SO$$_4$$.

WAEC 1998
3990

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, a 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 of each test.

(a) Add about 10cm$$^3$$ of distilled water to all of C in a boiling tube. Shake the mixture and filter: Keep both the filtrate and the residue.

(b) Divide the filtrate into two portions.

(i) To the first portion, add about 2cm$$^3$$ of barium chloride solution, followed by dilute hydrochloric acid in excess. Warm the mixture and identify any gas evolved.

(ii) To the second portion, add few drops of acidified potassium tetraoxomanganate (VIl) solution and shake.

(C) Put the residue in a test tube and add about 3cm$$^3$$ of dilute hydrochloric acid Warm gently and identify any gas evolved. Keep the mixture.

(d) Divide the clear solution from (c) above into two portions

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

(ii) To the second, add aqueous ammonia in drops and then in excess.

WAEC 1998