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WAEC 2021 Chemistry Practical Questions and Answers for 14th September 2021

WAEC 2021 Chemistry Practical Questions and Complete Answers for Tuesday 14th September
2021

WAEC 2021 Chemistry Practical Questions: WAEC Chemistry Practical examination which is known to be very tough has been simplified here. This is so since we have provided on this article WAEC expo questions for Chemistry Practical and past random repeated questions for free. Stay focused on this page to see them below.

WAEC 2021 Chemistry Practical Tuesday 14th September, 2021

Chemistry 3 (Practical) (Alternative A) (1st set) – 9:30am – 11:30pm (2hrs)
Chemistry 3 (practical)(Alternative A) (2nd set) – 12:00pm – 2:00pm

2021 WAEC CHEMISTRY PRACTICAL ANSWERS

The West African Examinations Council (WAEC) is an examination board that conducts the West African Senior School Certificate Examination (WASSCE), for University and Jamb entry examination in West Africa countries. In a year, over three million candidates registered for the exams coordinated by WAEC.

WAEC 2021 Chemistry Practical Questions and Answers  Expo for 14th September 2021

1. A is 0.100 mol dm-3 solution of an acid. B is a solution KOH containing 2.8 g per 500 cm3.
(a) Put A into the burette and titrate it against 25.0 cm3 portions B using methyl orange as indicator. Repeat the titration to obtain consistent titres.  Tabulate your readings and calculate the average volume of A used.

(b) From your results and the information provided above, calculate the:
(i) number of moles of acid in the average titre;
(ii) number of moles of KOH in the volume of B pipetted;
(iii) mole ratio of acid to base in the reaction
[H = 1.00, O = 16.0, K = 39.0]

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ANS: (a) titration soon.

(b) (i) number of moles of acid = 0.100 x VA
1000
=   X mole(s) [3sig. Fig to score]

1000cm3 contains 0.100 mole(s)
VA will contain 0.100 x VA
1000
=   X moles [3 Sig. Fig. to score]

(ii) Number of moles of KOH in B
500cm3 of B contains 2.8g of KOH
1000cm3 of B will contain 2.8 x 1000 = 5.6 KOH
500
Molar mass of KOH = 39 + 16 + 1 or 56 gmol-1

Conc of B = 5.6  = 0.100 mol dm-3
56

WAEC 2021 Chemistry Practical Questions and Answers for 14th September 2021

(iii) Mole ratio of acid to base = X: Y to nearest whole number ratio.

2. C is a mixture of two salts. Carry out the following exercises on C. Record your observations and identify any gas(es) evolved. State the conclusion drawn from the result of each test.

(a) Put all of C into a boiling tube and add about 5cm3 of distilled water.  Stir thoroughly and filter. Keep both the residue and the filtrate.

(b) To about 2 cm3 of the filtrate, add few drops of Pb(NO3)2(aq)‑Boil the mixture and then allow to cool.

(c) (i) Put the residue in a test tube and add dilute HNO3. Shake the mixture and divide the solution into two portions.
(ii) To the first portion from (c)(i), add NaOH(aq) in drops and then in excess.
(iii) To the second portion from (c)(i), add aqueous ammonia in drops and thein in excess.

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ANS:

TEST OBSERVATION INFERENCE
a)  C+water, mixture stirred
and filtered
Partly dissoves/ soluble Colourless filtrate
White residue (do not accept ppt /solid)
C contains soluble and insoluble salts
b) Filtrate + Pb (NO3)2(aq). Boiled then cooled White precipitate formed
Precipitate dissolves
Precipitate re-appeares
Cl-, SO42- or CO32.
Cl- present
Cl- confirmed
c) (i) Residue + dil HNO3 Effervescence /bubles /gas evolved colourless, odourless gas. Gas turns lime water milky. CO2 evolved from CO32-
(ii)  Solution from (c)(i) + NaOH(aq) in drops then in excess White gelatinous ppt formed. Precipitate dissolves Zn2+ or A13+Zn2+ or A13+
(iii) Solution from (c)(i) + HN3(aq) in drops then in excess White gelatinous. Precipitate forms. Precipitate dissolves Zn2+ or A13+Zn2+ confirmed

3. (a) Explain briefly the observations in each of the following processes:
(i) when carbon(IV) oxide is bubbled through lime water, it turns milky but the milkiness disappears when the gas is bubbled for a long time;
(ii) a precipitate of calcium hydroxide is insoluble in excess sodium hydroxide solution whereas that of lead (II) hydroxide is soluble.

(b) (i) What is a primary standard solution?
(ii) Calculate the mass of sodium trioxocarbonate(IV) required to prepare 250 cm3 of 0.15 moldm-3 solution.
[Na = 23.0; O = 16.0; C = 12.0]

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(c) Name one gas that can be collected by:
(i) upward displacement of air;
(ii) downward displacement of air.

WAEC 2021 Chemistry Practical Questions and Answers for 14th September 2021

ANS: (a) (i): Insoluble CaCO3 formation is responsible for the milkness produce when CO2 is bubbled through lime water while the disappearance of milkness is due to the formation of soluble Ca(HCO3)2.
Lime water turns milky with CO2 because  CaCO3/ CaCO3(s)  is formed. Milkiness disappear when excess CO2 reacts with CaCO3 in water medium forming the soluble Ca(HCO3)2/ Ca(HCO3)2 (aq).
(ii) Calcium hydroxide is not amphoteric. Does not react with an alkali NaOH whereas lead (II) hydroxide is amphoteric so reacts with excess NaOH.

(b) (i) Primary standard solution is one whose concentration is known and can be used to standardize another solution.
(ii)    M (Na2CO3)    =  106 gmol-1
m(Na2CO3)     =  C x M x V
=   0. 15 x 106 x 0. 25
=   3. 98 g

(c) (i) Carbon(IV) oxide, sulphur (IV) oxide, hydrogen chloride, oxygen, nitrogen (IV) oxide, chlorine, hydrogen sulphide.
(ii) Ammonia, oxygen, hydrogen, methane.

DISCLAIMER! These are not real WAEC Chemistry Practical questions but likely repeated questions over the years to help candidate understand the nature of their examinations. Ensure to take note of every questions provided on this page.


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