### Chemistry Past Questions

3991

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 14.0gdm$$^{-3}$$ of potassium hydrogen tetraoxosulphate (VI). B is a solution of sodium hydroxide.

(a) Put A into the burette and titrate with 20.0cm$$^{-3}$$ 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.

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

(i) concentration of A in mol dm$$^{3}$$

(ii) concentration of B in g dm$$^3$$

(iii) volume of A (in dm$$^{-3}$$) that would produce one mole of Sodium tetraoxosulphate (VI) in solution. The equation for the reaction is:

2KHSO$$_{4(aq)}$$ + 2NaOH$$_{(aq}$$ $$\to$$ K$$_2$$SO$$_{4(aq)}$$ + NaSO$$_{4(aq)}$$ + 2H$$_2$$O$$_{(l)}$$ [H = 1; O = 16, Na = 23, KHSO$$_4$$ =  136gmol$$^{-2}$$]

WAEC 1998
3992

(a) Name one laboratory apparatus/set-up for:

(i) determining the heat of neutralization:

(ii) decomposing water into hydrogen and oxygen.

(b) Outline a suitable procedure for distinguishing between glucose and cellulose using

(i) one physical test apart from tasting.

(ii) one chemical test.

(c) Draw a labelled sketch to illustrate the separation of a mixture by sublimation.

(ii) Give two examples of substances that are sublime.

(d)(i) Mention one salt which produces brown fumes on being heated strongly

(ii) What is the action of the brown fumes mentioned in (i) above on litmus.

(iii) Give one reason why it is not advisable to collect nitrogen by displacement of air [N - 14].

WAEC 1997
3993

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 state the conclusion you draw from the result of each test.

(a)(i) Put half of C in a test tube and add about 5cm$$^3$$ of distilled water. Test with litmus.

(ii) Put the rest of C in a test tube and add about 5cm$$^3$$  of dilute hydrochloric acid. Identify any gases evolved.

(b)(i) Put half of D in a test tube. Add about 5cm$$^3$$  of sodium hydroxide solution and warm. Identify any gases evolved.

(ii) Put the rest of D in a test tube and add about 5cm$$^3$$  of distilled water. Mix thoroughly. Add about 2cm$$^3$$ of barium chloride solution, followed by dilute hydrochloric acid in excess.

WAEC 1997
3994

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 is 0.50 mol dm$$^{-3}$$ hydrochloric acid. B is 0.025 mol dm$$^{-3}$$ of a trioxocarbonate (IV) salt.

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

(b) From your results, calculate the mole ratio of acid to trioxocarbonate (IV)  in the reaction, expressing your answer as a whole number ratio of one.

(c) Given that B contains 7.2g dm$$^{-3}$$ of the hydrated trioxocarbonate (IV) salt, calculate the:

(i) concentration of anhydrous salt in B in g dm$$^{-3}$$ [Molar mass of anhydrous salt in B = 106g]

(ii) percentage of water of crystallization in the hydrated salt.

WAEC 1997
3995

Mention one suitable laboratory procedure for

(i) removing carbon (IV) oxide from a sample of air

(ii) determining whether a given sample of water is pure or not;

(iii) concentrating a dilute solution of sodium chloride.

(b) Use the information provided in the table below to outline a suitable procedure for separating a mixture containing P, Q and R into its Components.

 Component Solubility in tetrachloromethane Solubility in water P Q R Insoluble  Soluble Insoluble Insoluble  Slightly soluble  soluble

(c)(i) Draw a labelled sketch to illustrate the collection of gases by upward displacement of air.

(ii) A gas S, with a rotten egg smell, was evolved when dilute hydrochloric acid was added to T which is a salt of iron (II). S decolorized acidified potassium tetraoxomanganate (VIl) solution and a yellow precipitate V was also obtained. Identify S, T and V.

(iii) State what would be observed on bubbling chlorine through a solution of potassium bromide.

WAEC 1996