WAEC Chemistry Practical Past Questions And Answers PDF
by Kowsalya | Updated May 18, 2023
WAEC Chemistry Practical Past Questions and Answers
If you are among the many candidates who will be taking the WAEC Chemistry exam, there is a helpful resource available to guide you during your preparation.
The WAEC Chemistry Practical Past Questions is an excellent study material to aid in your exam readiness. Alongside other study materials, this past question solution can assist in tackling pending problems and increase your chances of scoring higher than your competitors.
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What are WAEC Chemistry Practical Past Questions?
To begin with, Waec Chemistry Practical Past Questions is a collection of previous questions that candidates have been asked to answer in order to qualify for a certified WAEC certificate or result, which is useful for both employment and admission processes.
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WAEC Chemistry Practical Past Questions and Answers
Given below are some WAEC Chemistry Practical Past Questions and answers, these are just practice questions.
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 an 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
ANS: 1 (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
(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) that 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 then in excess.
ANS: 2
TEST
OBSERVATION
INFERENCE
a) C+water, mixture stirred
and filtered
Partly dissolves/ soluble Colourless filtrate
The 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-appears
Cl-, SO42- or CO32.
Cl- present
Cl- confirmed
c) (i) Residue + dil HNO3
Effervescence /bubbles/gas evolved colorless, odorless 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]
(c) Name one gas that can be collected by:
(i) upward displacement of air;
(ii) downward displacement of air.
ANS: 3 (a) (i): Insoluble CaCO3 formation is responsible for the milkiness produced 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 disappears when excess CO2 reacts with CaCO3 in a 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 sulfide.
(ii) Ammonia, oxygen, hydrogen, methane.
4. Which of the following is used as an indicator in titrating a strong acid with a weak base?
- Methyl orange
- Methyl red
- Sodium hydroxide
- Phenolphthalein
Answer: (a), Methyl orange is used as an indicator in titrating a strong acid with a weak base.
5. Which of the following is used as an indicator in titrating a weak acid with a strong base?
- Methyl orange
- Methyl red
- Sodium hydroxide
- Phenolphthalein
Answer: (d), Phenolphthalein is used as an indicator in titrating a weak acid with a strong base.
6. What is the role of an indicator in a reaction?
- To detect the end point of the titration
- Assist reactants to react quickly
- To provide a surface for the reaction
- To increase the rate of a reaction
Answer: (a), The role of an indicator in a reaction is to detect the end point of the titration.
7. What is the primary objective of titration?
- To find the concentration of an unknown acid or base
- To find the volume of an unknown acid or base
- To find the pH of an unknown acid or base
- To find the pressure of an unknown acid or base
Answer: (a), The primary objective of titration is to find the concentration of an unknown acid or base.
WAEC Chemistry Practical Past Questions And Answers - FAQs
WASSCE - conducted in May - June is called the SSCE.
WASSCE - conducted from November - December is called the WAEC or GCE.