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Chemistry
WAEC / WASSCE 1995
Metals, Transition Elements & Extraction
The function of limestone in the extraction of iron in the blast furnace is
A
removal of the earthly impurities
B
decomposition of the iron ore
C
conversion of iron (lll) to iron (ll) compounds
D
generation of heat for the process
E
conversion of coke to carbon(ll)oxide
medium Difficulty
Verified Correct Answer: Option A
Chemical Principles & Mechanism
No expanded working has been attached for this question yet. The verified answer is Option A.
Source: Myschool Past Questions Archive (Record #36423)
Chemistry
WAEC / WASSCE 1995
Stoichiometry, Mole Concept & Volumetric Analysis
Metals which react with steam only when they are red-hot include
A
copper
B
sodium
C
calcium
D
gold
E
iron
medium Difficulty
Verified Correct Answer: Option E
Chemical Principles & Mechanism
No expanded working has been attached for this question yet. The verified answer is Option E.
Source: Myschool Past Questions Archive (Record #36426)
Chemistry
WAEC / WASSCE 1995
Stoichiometry, Mole Concept & Volumetric Analysis
Copper (ll) tetraoxosulphate (VI) is often added to swimming pools because it
A
prevents the growth of algae
B
coagulates suspended particles
C
neutralizes dissolved gases in water
D
reacts with any excess chlorine present
E
increases the amount of dissolved oxygen
medium Difficulty
Verified Correct Answer: Option A
Chemical Principles & Mechanism
No expanded working has been attached for this question yet. The verified answer is Option A.
Source: Myschool Past Questions Archive (Record #36431)
Chemistry
WAEC / WASSCE 1995
Stoichiometry, Mole Concept & Volumetric Analysis
The following salts dissolve readily in cold water except
A
CaCI2
B
PbSO4
C
(NH4)2SO4
D
Na2CO3
E
Na2SO3
medium Difficulty
Verified Correct Answer: Option B
Chemical Principles & Mechanism
No expanded working has been attached for this question yet. The verified answer is Option B.
Source: Myschool Past Questions Archive (Record #36432)
Chemistry
WAEC / WASSCE 1995
Stoichiometry, Mole Concept & Volumetric Analysis
What is the amount (in mole) of hydrogen gas that would be produced if 0.6 mole of hydrochloric acid reacted with excess zinc according to the following equation? Zn(s) + 2HCI(aq) → ZnCI2(aq) + H2(g)
A
0.1 mole
B
0.2mole
C
0.3 mole
D
1.0 mole
E
2.9 moles
medium Difficulty
Verified Correct Answer: Option C
Chemical Principles & Mechanism
No expanded working has been attached for this question yet. The verified answer is Option C.
Source: Myschool Past Questions Archive (Record #36438)
Chemistry
WAEC / WASSCE 1995
Stoichiometry, Mole Concept & Volumetric Analysis
Solution
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 6.3g dm\(^{-3}\) of impure ethanoic acid. B is 0.10mol. dm\(^{-3}\) sodium hydroxide sodium hydroxide solution.
(a) Put A into the burette and titrate with 20.0cm\(^3\) or 25.0cm\(^3\) portions of B using phenolphthalein as indicator. Record the volume of your pipette Record the volume of your pipette. Tabulate your burette readings and calculate the volume of A used.
(b) From your result and the information provided, calculate the
(i) concentration of solution A in mol.dm\(^{-3}\)
(ii) Concentration of solution A in dm\(^{-3}\) and hence the percentage purity of the ethanoic acid,
(iii) Volume of solution A that would neutralize a solution containing 0.005 mole of sodium hydroxide. The equation for the reaction is;
H\(_2\)C\(_2\)O\(_{4(aq)}\) + 2NaOH\(_{(aq)}\) \(\to\) Na\(_2\)C\(_2\)O\(_{(aq)}\) + 2H\(_2\)O\(_{(l)}\) [H = 1; C = 12. O = 16]
(c)(i) What would be the colour of methylorange indicator in solution B?
(ii) Give the reason why methylorange is not a suitable indicator for titration.
A
0.1 mole
B
0.2mole
C
0.3 mole
D
1.0 mole
E
2.9 moles
medium Difficulty
Verified Correct Answer: Option C
Chemical Principles & Mechanism
Volume of pipette/base used = 25cm\(^3\)
Indicator - phenolphthalein
Burette readings
Rough
1st
2nd
3rd
Final burette readings
20.80
41.45
20.70
25.60
Initial burette readings
0.00
20.80
0.00.
5.00
volume of acid used
20.80
20.65
20.70
20.60
Average litre value = \(\frac{20.65 + 20.70 + 20.60}{3}\) = 20.65 cm\(^{3}\)
(b)(i) Equation for the reaction; H\(_2\)C\(_2\)O\(_{4(aq)}\) + 2NaOH\(_{(aq)}\) + 2NaOH\(_{(aq)}\) \(\to\) Na\(_2\)C\(_2\)O\(_{(aq)}\) + 2H\(_2\)O
From the equation, mole ratio of acid to base is 1 : 2
Amount of NaOH in 25cm\(^3\) of B = \(\frac{25 \times 0.10}{1000}\) = 0.0025 mol.dm\(^{-3}\)
Amount of acid in 20.65 cm\(^3\) of A = \(\frac{25 \times 0.10}{2 \times 20.65}\)
= 0.60 mol.dm\(^{-3}\)
(ii) Molar concentration in gm/dm\(^{-3}\) of H\(_2\)C\(_2\)O\(_4\) = (2 x 1) + (2 x 1) + (2 x 12) + (4 x 16) + 90g
mass of H\(_2\) C\(_2\)O\(_4\) = (2 x 1) + (2 x 12) + (4 x 16) + 90g
mass of H\(_2\) C\(_2\)O\(_4\) in 1dm\(^3\) of A = \(\frac{90 \times 25 \times 0.1}{2 \times 20.65}\)
= \(\frac{225}{41.3} = 5.45g\)
mass of H\(_2\) C\(_2\)O\(_4\) in 1dm\(^3\) of A = 6.3g
% purity of H\(_2\) C\(_2\)O\(_4\) = \(\frac{5.45}{6.3} \times \frac{100}{1}\)
= 86.51%
(iii) 25dm\(^3\) of 0.10 mol. dn\(^3\) NaOH contains = \(\frac{25 \times 010}{1000}\) = 0.0025
20.65 cm\(^3\) of a neutralised 0.0025 mole NaOH
0.005 mole NaOH will be neutralised by \(\frac{20.65 \times 0.005}{0.0025}\) = 41.3cm\(^3\)
(c)(i) Methyl orange turns yellow
(ii) Ethanoic acid is a weak acid while sodium hydroxide is a strong base, Methyl orange is not suitable for the titration of a weak acid with strong bases because the endpoint will not coincide with the pH at which the indicator exhibits its colour change.
Source: Official Exam / Past Question Archive
Chemistry
WAEC / WASSCE 1995
Nature of Matter & Separation Techniques
Solution
(a) State three reasons why air is classified as a mixture.
(b) List two methods that can be used to separate a mixture of iodine crystals and iron filings.
medium Difficulty
Verified Correct Answer: Option
Chemical Principles & Mechanism
(a) Three reasons why air is classified as a mixture include:
(i) The composition of air variables
(ii) The components can be easily obtained/separated by physical means
(iii) The constituents of air still retain their individual properties.
(b) The two methods include (i) Sublimation (ii) Magnetization
Source: Myschool Past Questions Archive (Record #54363)
Chemistry
WAEC / WASSCE 1995
Nature of Matter & Separation Techniques
Solution
What name is given to each of the following? The
(a) irregular random movement of smoke particles in air.
(b) existence of an element in various forms in the same physical-state
(c) disintegration of atomic nuclei, accompanied with radiation emission.
(d) conversion of a solid difitrunto vapour without melting.
medium Difficulty
Verified Correct Answer: Option
Chemical Principles & Mechanism
(a) Brownian motion
(b) Allotropy
(c) Radioactivity
(d) Sublimation.
Source: Myschool Past Questions Archive (Record #54364)
Chemistry
WAEC / WASSCE 1995
Acids, Bases, pH & Salts
Solution
(a)(i) Explain the term pH
(ii) If sodium hydroxide solution were added to a solution of a strong acid, what would happen to the pH of the solution?
(b) Give one example of each of the following:
(i) acidic oxide
(ii) acid salt.
medium Difficulty
Verified Correct Answer: Option
Chemical Principles & Mechanism
(a)(i) pH is a measure of the acidity or alkalinity of a solution.
(ii) The pH of the acids solution would increase
(b)(i) Example of acidic oxide is sulphur (IV) oxide (SO\(_2\))
(ii) Example of acid salt is sodium hydrogen tetraoxosulphate(VI)
Source: Myschool Past Questions Archive (Record #54365)
Chemistry
WAEC / WASSCE 1995
Kinetic Theory of Matter & Gas Laws
Solution
(a)(i) Sketch a graph to illustrate Charles' law.
(ii) A gas occupies 500 cm\(^{ 3}\) at 2TC. calculate its volume at 40^\circC constant pressure.
(b) List two gases that are used as refrigerant
medium Difficulty
Verified Correct Answer: Option
Chemical Principles & Mechanism
(a)(i)
(ii) \(\frac{v}{T} = \frac{v}{T}\)
\(\frac{500}{300} = \frac{v}{313}\)
\(v_2 = \frac{500 \times 313}{300}\)
\(v_2 = \frac{500 \times 313}{300}\)
\(v_2 = 522cm^3\)
(b) Two gases that are used as refriger are;
(i) Ammonia (NH\(_3\)) and
(ii) Carbon dioxide (CO\(_2\))
Source: Myschool Past Questions Archive (Record #54366)
Chemistry
WAEC / WASSCE 1995
Organic Chemistry I: Hydrocarbons & Crude Oil
Solution
(a) State the type of reaction involved in the conversion of:
(i) proteins.to amino acids:
(ii) ethanol to ethene;
(iii) benzene to bromobenzene
(b) Write an equation to show that ethene reasts with hydrogen in the presence of finely divided nickel.
medium Difficulty
Verified Correct Answer: Option
Chemical Principles & Mechanism
(a)(i) Hydrolysis
(ii) Dehydration
(iii) Bromination or substitution reactions.
(b) C\(_2\)H\(_4\) + H\(_2\) —› C\(_2\)H\(_6\)
Source: Myschool Past Questions Archive (Record #54367)
Chemistry
WAEC / WASSCE 1995
Electrolysis & Electrochemical Cells
Solution
(a) Name the device used for producing an electric current from a chemical
(b) Copy and complete the table below.
Electrolyte
Product at the anode (carbon)
Product at the cathode (carbon)
Dilute NaCl\(_{(aq)}\)
Concentrated NaCI\(_{(aq)}\)
medium Difficulty
Verified Correct Answer: Option
Chemical Principles & Mechanism
(a) The device is electro chemical cell or voltaic cell
(b)
Electrolyte
Product at the anode (carbon)
Product at the cathode (carbon)
Dilute NaCl\(_{(aq)}\)
Concentrated NaCI\(_{(aq)}\)
Oxygen (O\(_2\))
Chloride (Cl\(_2\))
Hydrogen (H\(_2\))
Hydrogen (H\(_2\))
Source: Myschool Past Questions Archive (Record #54368)
Chemistry
WAEC / WASSCE 1995
Air & Environmental Chemistry
Solution
(a) Mention the chemical substance manufactured starting from each of the foirownc sets of materials:
(i) sugar and yeast;
(ii) ammonia, air and water;
(iii) vegetable oil and caustic alkali.
(b) State one air pollutant generated during the manufacture of fertilizers.
medium Difficulty
Verified Correct Answer: Option
Chemical Principles & Mechanism
(a)(i) The chemical substance is ethanol (C\(_2\)H\(_5\)OH)
(ii) The chemical substance is Trioxonitrate(V) acid
(iii) The chemical substance is soap
(b) One air pollutant is sulphur(IV) oxide (SO\(_2\)) or nitrogen(IV) oxide (NO\(_2\))
Source: Myschool Past Questions Archive (Record #54369)
Chemistry
WAEC / WASSCE 1995
Oxidation, Reduction & Redox Reactions
Solution
(a) What is the change in oxidation state of chromium in the reaction represented by the following equation?
3SO\(_2\) + Cr\(_2\)O\(^2_{-7}\) + 2H\(^+\) -> 3SO\(_4^{2-}\) + 2Cr\(^{3+}\) + H\(_2\)O
(b) Use the half equations given below to deduce the equation for the reaction between iron(II) ions and heptaoxodichromate (VI) ions in acidic solution.
Fe\(^{2+}\) --> Fe\(^{3+}\) + e\(^-\)
Cr\(_2\)O\(^{2-}_7\) + 14H\(^+\) + 6e\(^-\) ----> 2Cr\(^{3+}\) + 7H\(_2\)O.
medium Difficulty
Verified Correct Answer: Option
Chemical Principles & Mechanism
(a) From +6 to +3
(b) The reaction involves the transfer of 6 electrons from 6Fe 2+ to Cr\(_2\)O\(_7\)
SO, 6Fe\(^{2+}\) \(\rightleftharpoons\) 6Fe\(^{3+}\) + 6e\(^-\)
The addition of the 2 half cell equations gives Cr\(_2\)O\(_7^{2-}\) + 14H\(^+\) — 6Fe\(^{2+}\) \(\to\) 2Cr\(^{3+}\) + 6Fe\(^{3+}\) + 6Fe\(^{3+}\) + 7H\(_2\)O.
Source: Myschool Past Questions Archive (Record #54371)
Chemistry
WAEC / WASSCE 1995
Stoichiometry, Mole Concept & Volumetric Analysis
Solution
(a) Mention one process apart from respiration, which increases the amount of carbon (IV) oxide in the atmosphere.
(b)(i) State one use of sodium hydrogentrioxocarbonate (IV).
(ii) Write an equation to show the action of heat on sodium hydrogentrioxocarbonate(IV).
medium Difficulty
Verified Correct Answer: Option
Chemical Principles & Mechanism
(a) One process is combustion of carbon and carbon compounds
(b)(i) It is used for making baking powder
(ii) 2NaHCO\(_3\) ----> Na\(_2\)CO\(_3\) + H\(_2\)O + CO\(_2\).
Source: Myschool Past Questions Archive (Record #54373)