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Chemistry
WAEC / WASSCE 2017
Electrolysis & Electrochemical Cells
Solution
(a)(i) Describe briefly how trioxonitrate (V) ions could be tested for in the laboratory.
(ii) State two uses of each of the following compounds: I. sodium chloride; II. sodium trioxocarbonate (IV).
(b) Write balanced equations for the reactions involved in the extraction of iron in the blast furnace.
(ii) State Faraday's first law of electrolysis.
(iii) State two applications of electrolysis.
(c) Concentrated tetraoxosulphate (VI) acid is added to sugar crystals in a beaker. State what would be observed. Explain briefly your answer.
(d) Write an equation for the reaction of zinc powder with:
(i) dilute tetraoxosulphate (VI) acid;
(ii) concentrated tetraoxosulphate (VI) acid.
(e) What property of concentrated tetraoxosulphate (VI) acid is shown in (d)(ii)
medium Difficulty
Verified Correct Answer: Option
Chemical Principles & Mechanism
(a)(i)
Test
Observation
i.
Sample of concentrated H\(_2\)SO\(_4\) + heat
Brown fumes of NO\(_2\) evolved
ii.
Sample + Copper + cone H\(_2\)SO\(_4\) and warm
Reddish brown fume of NO\(_2\)
iii.
Cold Sample solution + freshly prepared FeSO\(_4\) solution and followed by conc H\(_2\)SO\(_4\) (few drops) to the sample solution + freshly prepared FeSO\(_4\) in slant form
A brown ring observed between the junction of the acid and sample solution.
(ii) Two uses of each of the following compounds:
(1) Sodium Chloride - food seasoning, food preservative, glazing pottery/earthen ware. soap production, crude oil refilling, water softener, production of chlorine/hydrogen/ sodium metal, NaOH/NaClO\(_3\)/NaOCl/Na\(_2\)CO\(_3\) lowering melting point of ice preparation of freezing mixture. Used in tannery industry/tanning.
(2) Uses of sodium trioxocarbonate (IV) - Manufacture of glass/borax in detergents/ soaps, manufacture of paper softening hardwater, manufacture of NaOH treating (concentrated) acid splash, standardization of acids/analytical reagent.
(b)(i) Balanced equations for the reactions involved in the extraction of iron in the blast furnace.
C\(_{(g)}\) + O\(_{2(g)}\) ----> CO\(_{2(g)}\)
CO\(_{2(g)}\) + C\(_{(g)}\) --> 2CO\(_{(g)}\)
F\(e_2\)\(O_3\) + 3CO\(_{(g)}\) \(\to\) 2Fe + 3CO\(_{2(g)}\)
CaO + Si\(O_2\) -> CaSi\(O_3\)
CaC\(O_3\) -> CaO + C\(O_2\)
(ii) Faraday's first law of electrolysis states that the mass of an element discharged at the electrode is directly proportional to the quantity of electricity passed through the electrolyte.
(iii) Two applications of electrolysis are: Electroplating of metals, Extraction of metals, Purification of metals, Preparation of compounds/elements, Production of gases \(H_2\), \(O_2\), C\(l_2\) (any 2)
(c) Sugar crystals + concentrated \(H_2\)S\(O_4\) in a beaker. Observations are as follows:
(1) Concentrated acid dehydrates the sugar.
(2) A mass of carbon/black soot/ sugar charcoal is formed.
(3) Reaction is exothermic (heat evolved or released).
(d) Equations for the reaction of Zinc powder with dilute tetraoxosulphate (VI) acid:
(i) Zn\(_{(g)}\) + \(H_2\)SO\(_{4(aq)}\) -> ZnSO\(_{4(aq)}\) + H\(_{2(g)}\)
(ii) Reaction with dilute concentrated H\(_2\)SO\(_4\)
(iii) Zn\(_{(g)}\) + 2H\(_2\)SO\(_{4(aq)}\) -> ZnSO\(_{4(aq)}\) + SO\(_{2(g)}\) + 2H\(_2\)O\(_{(l)}\)
(e) Property of concentrated tetraoxosulphate (VI) acid shown in (d)(1) is oxidizing property.
Source: Myschool Past Questions Archive (Record #50826)
Chemistry
WAEC / WASSCE 2017
Stoichiometry, Mole Concept & Volumetric Analysis
Solution
All your burette readings (initials 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 booklet.
State what would be observed if the following reactions are carried out in the laboratory:
(i) methyl orange is dropped into a solution of lime juice:
(ii) hydrogen sulphide gas is bubbled through Iron (III) chloride solution:
(iii) sulphur (IV) oxide gas is bubbled into acidified solution of KMnO\(_4\):
(iv) ethanoic acid is added to a solution of Ka\(_2\)CO\(_3\)
medium Difficulty
Verified Correct Answer: Option
Chemical Principles & Mechanism
(a)(i) Solution of lime juice turns to pink or red,
(ii) The FeCl\(_3\) solution changes colour from brown to green and a yellow deposit.
(iii) The purple colour of KmnO\(_4\) solution turns colourless or decolourised.
(iv) The solution of K\(_2\)CO\(_3\) reacts with the addition of ethanoic acid to evolve a colourless, odourless gas with bubbling or effervescence
Source: Myschool Past Questions Archive (Record #59979)
Chemistry
WAEC / WASSCE 2017
Nature of Matter & Separation Techniques
Solution
All your burette readings (initials 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 booklet.
F is 2 mixture of two inorganic salts. Carry out the following exercises on F. Record your observations and identify any gas(es) evolved. State the conclusions you draw from the result of each test.
(a) Put all of F in a beaker and add about 10 cm\(^3\) of distilled water. Stir well and filter. Keep the filtrate and the residue.
(b)(i) To about 2cm\(^3\) of the filtrate. add NaOH\(_{(aq)}\) in drops and then in excess.
(ii) To another 2cm\(^3\) portion of the solution, add a few drops of NH3\(_{(aq)}\) in drops and then in excess.
(c) To about 2cm\(^3\) of the solution, add a few drops of HNO\(_{3(aq)}\) followed by few drops of the drops of AgNO\(_{3(aq)}\)
(d)(i) Put all the residue into a clean test-tube and add HNO\(_{3(aq)}\)
(ii) To a portion of the solution from (d)(i)) add NaOH\(_{(aq)}\) in drops and then in excess.
medium Difficulty
Verified Correct Answer: Option
Chemical Principles & Mechanism
TEST
OBSERVATION
INTERFERENCE
(a)
F + distil water + stir + filter
Effervescence (bubbling) occurs. Colourless and odourless gas evolved after filtration pale blue/colourless filtrate and green residue
(b)(i)
Filtrate + NaOH\(_{(aq)}\) in drops
Then in excess
White precipitate formed
Precipitate insoluble in excess NaOH\(_{(aq)}\)
Ca\(^{2+}\)/pb\(^{2+}\)
Ca\(^{2+}\) present
(b)(ii)
Filtrate + NH\(_3\) \(_{(aq)}\) in drops
Then in excess
No visible reaction
No visible reaction
Ca\(^{2+}\) present
Ca\(^{2+}\) confirmed
(b)(i)
Filtrate + NaOH\(_{(aq)}\) in drops
Then in excess
Blue gelatinous precipitate formed
Precipitate insoluble in excess
Cu\(^{2+}\) is present
(b)(ii)
Filtrate + NH\(_3\) \(_{(aq)}\) in drops
Then in excess
Pale (light) blue gelatinous precipitate formed
Precipitate dissolves to form a deep blue solution
Cu\(^{2+}\)
Cu\(^{2+}\) confirmed
(c)
Filtrate + NHO\(_3\) \(_{(aq)}\) + AgNO\(_3\)\(_{(aq)}\)
No visible reaction
No gas involved
White precipitate formed
Cl\(^{-}\) present
(d)(i)
Residue + HNO\(_{3(aq)}\)
Effervescence occurs, colourless and odourless gas evolves that turn blue litmus paper to red and turns lime water milky
CO\(_{3(g)}\)
CO\(_{3^{2-}}\) present
(d)(ii)
Solution from (d)(i) + NaOH\(_{(aq)}\) in drops
Then in excess
Blue precipitate formed
present Precipitate insoluble in excess NaOH\(_{(aq)}\)
Cu\(^{2+}\)
Cu\(^{2+}\) present
Source: Myschool Past Questions Archive (Record #59980)
Chemistry
WAEC / WASSCE 2017
Stoichiometry, Mole Concept & Volumetric Analysis
Solution
All your burette readings (initials 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 booklet.
A is 0.200 moldm\(^3\) of HCl. C is a solution containing 14.3g of Na2C\(O_3\).xH\(_2\)O in 500 cm\(^3\) of solution.
a) Put A into the burette and titrate it against 20.0 cm\(^3\) or 25.0cm\(^3\) portions of C using methyl orange as indicator. Repeat the titration to obtain Consistent titre values. Tabulate vour results and calculate the average volume of A used. The equation for the reaction is;
Na\(_2\)CO\(_3\) . xH\(_2\)O + 2HCl\(_{(aq)}\) \(\to\) 2NaCl\(_{(aq)}\) + CO\(_{2(g)}\) + (x + 1)\(_3\)H\(_2\)O\(_{(l)}\)
(b) From your results and the information provided. calculate the:
(i) concentration of C in moldm\(^{-3}\)
(ii) concentration of C in gdm\(^{-3}\)
(iii) molar mass of Na\(_2\)CO\(_3\) . xH\(_2\)O
(iv) the value of x in Na\(_2\)CO\(_3\) . xH\(_2\)O. [H =1.0; C = 12.0; O = 16.0; Na = 23.0]
Credit will be given for strict adherence to the instruction, for observations precisely recorded and for accurale references. All tests. obsenations and influences must be cleary entered in the booklet in ink at the same time they are made.
medium Difficulty
Verified Correct Answer: Option
Chemical Principles & Mechanism
Indicator = Methyl Orange
Volume of the base used = 25.00cm\(^3\)
Titration
Rough Titre
1st Titre
2nd Titre
3rd Titre
Final burette readings cm\(^3\)
24.70
24.80
24.70
24.90
Initial burette reading cm\(^3\)
0.00
0.00
0.00
0.00
Volume of acid used cm\(^3\)
24.70
24.80
24.70
24.90
Average Titre = \(\frac{1st + 2nd + 3rd}{3}\)
= \(\frac{24.80 + 24.70 + 24.90}{3}\)
= 24.80cm\(^3\)
Alternatively 2 concordant titres can be used to calculate average titre
Equation of thereaction; Na\(_2\)CO\(_3\).XH\(_2\)O + 2HCl\(_{(aq)}\) \(\to\) 2Nacl\(_{(aq)}\) \(\to\) 2Nacl\(_{(aq)}\) + CO\(_{2(aq)}\) + (X + 1)H\(_2\)O\(_{(l)}\)
\(\frac{C_AV_A}{C_BV_B} = \frac{n_A}{n_B}\)
C\(_A\) = Molar concentration of HCl\(_{(aq)}\) in moldm\(^{3}\)
V\(_A\) = Volume of acid used in cm\(^3\) = 24.80cm\(^3\)
C\(_B\) = Molar concentration of Na\(_2\)Cu\(_3\) . xH\(_2\)O in molddm\(^3\)
n\(_A\) = 2
n\(_B\) = 1
(b)(i) Concentration of C in moldm\(^{-3}\) = ?
From the equation reaction;
\(\frac{C_AV_A}{C_BV_B} = \frac{n_A}{n_B}\)
C\(_A\) = 0.200 molddm\(^{-3}\)
C\(_B\) = ?
V\(_A\) = 24.80 cm
V\(_B\) = 25.00 cm\(^3\)
Substitution of known values
\(\frac{0.200 \times 24.80}{C_B \times 25.00} = \frac{2}{1}\)
C\(_B\) = \(\frac{1 \times 0.200 \times 24.80}{2 \times 25.00}\)
C\(_B\) = 0.0992 moldm\(^{-3}\)
(ii) Concentration of C in gdm\(^3\) = ?
500 cm\(^2\) \(\to\) 14.3 g
1000cm\(^3\) \(\to\) \(\frac{14.3}{500}\) x 1000g
= 28.6 dm\(^{-3}\)
(iii) Molar mass of Na\(_2\)CO\(_3\) . XH\(_2\)O
Molar conc in moldm\(^{-3}\) = \(\frac{\text{conc. in gdm}^{-3}} {\text{molar mass} }\)
Molar mass gmol\(^{-1}\) = \(\frac{\text{conc in g dm}^{-3}}{\text{molar conc.in moldm}^{-3}}\)
\(\frac{28.6 gdm^{-3}}{0.0992 moldm^{-3}}\)
= 288.3065
= 288 gmol\(^{-1}\)
(iv) Value of x in Na\(_2\)CO\(_3\) . xH\(_2\)O?
[H = 1.0, C = 12.0, O = 16.0, Na = 23.0]
N\(_2\)CO\(_3\) . xH\(_2\)O = 288
2(23) + 12 + 3 (16) + x(2(1) + 16) = 288
46 + 12 +48 +18x = 288
106 + 18x = 288
18x = 288 - 106
18x = 182
x = \(\frac{182}{18}\)
x = 10.11
x = 10
Source: Myschool Past Questions Archive (Record #59981)
Chemistry
WAEC / WASSCE 2017
Stoichiometry, Mole Concept & Volumetric Analysis
Solution
All your burette readings (initials 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 booklet.
A is 0.200 moldm\(^3\) of HCl. C is a solution containing 14.3g of Na2C\(O_3\).xH\(_2\)O in 500 cm\(^3\) of solution.
a) Put A into the burette and titrate it against 20.0 cm\(^3\) or 25.0cm\(^3\) portions of C using methyl orange as indicator. Repeat the titration to obtain Consistent titre values. Tabulate vour results and calculate the average volume of A used. The equation for the reaction is;
Na\(_2\)CO\(_3\) . xH\(_2\)O + 2HCl\(_{(aq)}\) \(\to\) 2NaCl\(_{(aq)}\) + CO\(_{2(g)}\) + (x + 1)\(_3\)H\(_2\)O\(_{(l)}\)
(b) From your results and the information provided. calculate the:
(i) concentration of C in moldm\(^{-3}\)
(ii) concentration of C in gdm\(^{-3}\)
(iii) molar mass of Na\(_2\)CO\(_3\) . xH\(_2\)O
(iv) the value of x in Na\(_2\)CO\(_3\) . xH\(_2\)O. [H =1.0; C = 12.0; O = 16.0; Na = 23.0]
Credit will be given for strict adherence to the instruction, for observations precisely recorded and for accurale references. All tests. obsenations and influences must be cleary entered in the booklet in ink at the same time they are made.
A
is formed naturally
B
is cheap
C
can be recycled after use
D
cannot be regenerated once used up
medium Difficulty
Verified Correct Answer: Option D
Chemical Principles & Mechanism
Indicator = Methyl Orange
Volume of the base used = 25.00cm\(^3\)
Titration
Rough Titre
1st Titre
2nd Titre
3rd Titre
Final burette readings cm\(^3\)
24.70
24.80
24.70
24.90
Initial burette reading cm\(^3\)
0.00
0.00
0.00
0.00
Volume of acid used cm\(^3\)
24.70
24.80
24.70
24.90
Average Titre = \(\frac{1st + 2nd + 3rd}{3}\)
= \(\frac{24.80 + 24.70 + 24.90}{3}\)
= 24.80cm\(^3\)
Alternatively 2 concordant titres can be used to calculate average titre
Equation of thereaction; Na\(_2\)CO\(_3\).XH\(_2\)O + 2HCl\(_{(aq)}\) \(\to\) 2Nacl\(_{(aq)}\) \(\to\) 2Nacl\(_{(aq)}\) + CO\(_{2(aq)}\) + (X + 1)H\(_2\)O\(_{(l)}\)
\(\frac{C_AV_A}{C_BV_B} = \frac{n_A}{n_B}\)
C\(_A\) = Molar concentration of HCl\(_{(aq)}\) in moldm\(^{3}\)
V\(_A\) = Volume of acid used in cm\(^3\) = 24.80cm\(^3\)
C\(_B\) = Molar concentration of Na\(_2\)Cu\(_3\) . xH\(_2\)O in molddm\(^3\)
n\(_A\) = 2
n\(_B\) = 1
(b)(i) Concentration of C in moldm\(^{-3}\) = ?
From the equation reaction;
\(\frac{C_AV_A}{C_BV_B} = \frac{n_A}{n_B}\)
C\(_A\) = 0.200 molddm\(^{-3}\)
C\(_B\) = ?
V\(_A\) = 24.80 cm
V\(_B\) = 25.00 cm\(^3\)
Substitution of known values
\(\frac{0.200 \times 24.80}{C_B \times 25.00} = \frac{2}{1}\)
C\(_B\) = \(\frac{1 \times 0.200 \times 24.80}{2 \times 25.00}\)
C\(_B\) = 0.0992 moldm\(^{-3}\)
(ii) Concentration of C in gdm\(^3\) = ?
500 cm\(^2\) \(\to\) 14.3 g
1000cm\(^3\) \(\to\) \(\frac{14.3}{500}\) x 1000g
= 28.6 dm\(^{-3}\)
(iii) Molar mass of Na\(_2\)CO\(_3\) . XH\(_2\)O
Molar conc in moldm\(^{-3}\) = \(\frac{\text{conc. in gdm}^{-3}} {\text{molar mass} }\)
Molar mass gmol\(^{-1}\) = \(\frac{\text{conc in g dm}^{-3}}{\text{molar conc.in moldm}^{-3}}\)
\(\frac{28.6 gdm^{-3}}{0.0992 moldm^{-3}}\)
= 288.3065
= 288 gmol\(^{-1}\)
(iv) Value of x in Na\(_2\)CO\(_3\) . xH\(_2\)O?
[H = 1.0, C = 12.0, O = 16.0, Na = 23.0]
N\(_2\)CO\(_3\) . xH\(_2\)O = 288
2(23) + 12 + 3 (16) + x(2(1) + 16) = 288
46 + 12 +48 +18x = 288
106 + 18x = 288
18x = 288 - 106
18x = 182
x = \(\frac{182}{18}\)
x = 10.11
x = 10
Source: Official Exam / Past Question Archive
English Language
WAEC / WASSCE 2017
Antonyms (Opposite in Meaning)
In the following sentence, there is one underlined word and one gap. From the list of words lettered A to D, choose the one that is most nearly opposite in meaning to the underlined word and that will, at the same time, correctly fill the gap in the sentence.
Michael is stingy but his brother is _______
A
generous
B
kind
C
humane
D
hospitable
medium Difficulty
Verified Correct Answer: Option A
Grammar & Contextual Explanation
No expanded working has been attached for this question yet. The verified answer is Option A.
Source: Myschool Past Questions Archive (Record #48743)
English Language
WAEC / WASSCE 2017
Antonyms (Opposite in Meaning)
In the following sentence, there is one underlined word and one gap. From the list of words lettered A to D, choose the one that is most nearly opposite in meaning to the underlined word and that will, at the same time, correctly fill the gap in the sentence.
Success is the reward of _________, not indolence.
A
prudence
B
attentiveness
C
diligence
D
sharpness
medium Difficulty
Verified Correct Answer: Option C
Grammar & Contextual Explanation
No expanded working has been attached for this question yet. The verified answer is Option C.
Source: Myschool Past Questions Archive (Record #48747)
English Language
WAEC / WASSCE 2017
Antonyms (Opposite in Meaning)
In the following sentence, there is one underlined word and one gap. From the list of words lettered A to D, choose the one that is most nearly opposite in meaning to the underlined word and that will, at the same time, correctly fill the gap in the sentence.
I don't know how Yusuf became so proud; his parents have always been ______
A
gentle
B
noble
C
humble
D
simple
medium Difficulty
Verified Correct Answer: Option C
Grammar & Contextual Explanation
No expanded working has been attached for this question yet. The verified answer is Option C.
Source: Myschool Past Questions Archive (Record #48749)
English Language
WAEC / WASSCE 2017
Antonyms (Opposite in Meaning)
In the following sentence, there is one underlined word and one gap. From the list of words lettered A to D, choose the one that is most nearly opposite in meaning to the underlined word and that will, at the same time, correctly fill the gap in the sentence.
The once unknown musician became _____ in a very short time.
A
popular
B
accepted
C
respected
D
admirable
medium Difficulty
Verified Correct Answer: Option A
Grammar & Contextual Explanation
No expanded working has been attached for this question yet. The verified answer is Option A.
Source: Myschool Past Questions Archive (Record #48751)
English Language
WAEC / WASSCE 2017
Antonyms (Opposite in Meaning)
In the following sentence, there is one underlined word and one gap. From the list of words lettered A to D, choose the one that is most nearly opposite in meaning to the underlined word and that will, at the same time, correctly fill the gap in the sentence.
Issa is very much interested in education while his sister in ________
A
dull
B
indifferent
C
uncertain
D
serious
medium Difficulty
Verified Correct Answer: Option B
Grammar & Contextual Explanation
No expanded working has been attached for this question yet. The verified answer is Option B.
Source: Myschool Past Questions Archive (Record #48753)
English Language
WAEC / WASSCE 2017
Antonyms (Opposite in Meaning)
In the following sentence, there is one underlined word and one gap. From the list of words lettered A to D, choose the one that is most nearly opposite in meaning to the underlined word and that will, at the same time, correctly fill the gap in the sentence.
The comment I made at the conference was general; being ______ would have hurt some people.
A
ordinary
B
specific
C
tactful
D
candid
medium Difficulty
Verified Correct Answer: Option B
Grammar & Contextual Explanation
No expanded working has been attached for this question yet. The verified answer is Option B.
Source: Myschool Past Questions Archive (Record #48754)
English Language
WAEC / WASSCE 2017
Antonyms (Opposite in Meaning)
In the following sentence, there is one underlined word and one gap. From the list of words lettered A to D, choose the one that is most nearly opposite in meaning to the underlined word and that will, at the same time, correctly fill the gap in the sentence.
Buba was purposeful in his serch for a job but Bala was rather _____ about his.
A
patient
B
slow
C
lazy
D
casual
medium Difficulty
Verified Correct Answer: Option D
Grammar & Contextual Explanation
No expanded working has been attached for this question yet. The verified answer is Option D.
Source: Myschool Past Questions Archive (Record #48755)
English Language
WAEC / WASSCE 2017
Antonyms (Opposite in Meaning)
In the following sentence, there is one underlined word and one gap. From the list of words lettered A to D, choose the one that is most nearly opposite in meaning to the underlined word and that will, at the same time, correctly fill the gap in the sentence.
In recent tournaments i have seen amateurs play better than so-called _____
A
experts
B
veterans
C
specialists
D
professionals
medium Difficulty
Verified Correct Answer: Option D
Grammar & Contextual Explanation
No expanded working has been attached for this question yet. The verified answer is Option D.
Source: Myschool Past Questions Archive (Record #48757)
English Language
WAEC / WASSCE 2017
Antonyms (Opposite in Meaning)
In the following sentence, there is one underlined word and one gap. From the list of words lettered A to D, choose the one that is most nearly opposite in meaning to the underlined word and that will, at the same time, correctly fill the gap in the sentence.
Giraffes are attractive animals but snakes are _____
A
repulsive
B
ugly
C
poisonous
D
offensive
medium Difficulty
Verified Correct Answer: Option A
Grammar & Contextual Explanation
No expanded working has been attached for this question yet. The verified answer is Option A.
Source: Myschool Past Questions Archive (Record #48758)
English Language
WAEC / WASSCE 2017
Concord (Subject-Verb Agreement)
From the words lettered A to D, choose the word that best completes each of the following sentences.
Mr Uche was trying to _____ a list of his debtors
A
compare
B
compose
C
compound
D
compile
medium Difficulty
Verified Correct Answer: Option D
Grammar & Contextual Explanation
No expanded working has been attached for this question yet. The verified answer is Option D.
Source: Myschool Past Questions Archive (Record #48761)