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Chemistry
WAEC / WASSCE 2012
Matter & Separation Techniques
Solution
Consider the reaction represented by the following equation: CuO\(_{(s)}\) + H\(_2\)SO\(_{4(aq)}\) → CuSO\(_{4(aq)}\) + H\(_2\)O\(_{(l)}\). Which of the following factors will not affect the rate of the reaction?
A
Particle size of CuO(s)
B
Concentration of H2SO4(aq)
C
Temperature of the reacting mixture
D
Pressure of reaction system
medium Difficulty
Verified Correct Answer: Option D
Chemical Principles & Mechanism
The reaction rate between a solid and liquid will not be affected by pressure. Pressure majorly affects the reaction rate for gases.
Source: Myschool Past Questions Archive (Record #37797)
Chemistry
WAEC / WASSCE 2012
Electrochemistry and Redox
Which of the following devices function on redox reaction? l. Dry cell ll. Car battery III. Electric generator
A
l and lll only
B
ll and lll only
C
l and ll only
D
l, ll and lll
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 #37798)
Chemistry
WAEC / WASSCE 2012
Electrochemistry and Redox
Solution
The oxidation number of Fe in [Fe(CN)\(_6\)]\(^{3-}\) is
A
+3
B
+2
C
-2
D
-3
medium Difficulty
Verified Correct Answer: Option A
Chemical Principles & Mechanism
Let the oxidation number of Fe in the compound [Fe(CN)\(_6\)]\(^{3-}\) be x.
x + 6(-1) = -3
x - 6 = -3;
x = -3 + 6
x = +3
Source: Myschool Past Questions Archive (Record #37804)
Chemistry
WAEC / WASSCE 2012
Organic Chemistry
Solution
Consider the following reaction equation: C\(_{16}\)H\(_{34}\) → C\(_5\)H\(_{12}\) + C\(_{11}\)H\(_{22}\). The process represented by the equation is
A
cracking
B
fermentation
C
polymerization
D
reforming
medium Difficulty
Verified Correct Answer: Option A
Chemical Principles & Mechanism
In the reaction, a complex hydrocarbon is broken down into two simpler hydrocarbons. This is cracking.
Source: Myschool Past Questions Archive (Record #37807)
Chemistry
WAEC / WASSCE 2012
Matter & Separation Techniques
Solution
Which of the following substances would not produce ethanol when fermented?
A
Cane sugar
B
Glucose
C
Starch
D
Vinegar
medium Difficulty
Verified Correct Answer: Option D
Chemical Principles & Mechanism
Vinegar is a product from fermentation. It can be gotten from the fermentation of ethanol.
Source: Myschool Past Questions Archive (Record #37812)
Chemistry
WAEC / WASSCE 2012
Acids, Bases, and Salts
Solution
An alkanol can be prepared by the reaction of an alkene with
A
concentrated tetraoxosulphate (VI) acid
B
bromine tetrachloroethane
C
aqueous potassium tetraoxomanganate (VII)
D
sodium hydroxide solution
medium Difficulty
Verified Correct Answer: Option A
Chemical Principles & Mechanism
An alkene reacts with conc. H\(_2\)SO\(_4\) to yield an alkyl hydrogen tetraoxosulphate (VI). The compound formed undergoes hydrolysis when boiled with water to yield an alcohol.
Source: Myschool Past Questions Archive (Record #37813)
Chemistry
WAEC / WASSCE 2012
Stoichiometry & Mole Concept
A tertiary alkanol has a molecular formula C\(_4\)H\(_{10}\)O. What is the structural formula of the compound?
A
(CH 3)2CHCH2OH
B
CH3CH2CH(OH)CH3
C
(CH3)3COH
D
CH3CH2CH2CH2OH
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 #37814)
Chemistry
WAEC / WASSCE 2012
Matter & Separation Techniques
Solution
Which of the following industrial processes depends on the action of enzymes?
A
Liquefaction of air
B
Manufacture of soap
C
Brewing of beer
D
Catalytic cracking
medium Difficulty
Verified Correct Answer: Option C
Chemical Principles & Mechanism
The brewing of beer has to do with fermentation.
Source: Myschool Past Questions Archive (Record #37815)
Chemistry
WAEC / WASSCE 2012
Matter & Separation Techniques
Which of the following pollutants is not usually recycled?
A
Aluminium cans
B
Glass bottles
C
Nuclear wastes
D
Paper wastes
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 #37816)
Chemistry
WAEC / WASSCE 2012
Matter & Separation Techniques
A metal that is widely used in the manufacture of paints and overhead electric cables is
A
aluminium
B
copper
C
iron
D
lead
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 #37817)
Chemistry
WAEC / WASSCE 2012
Matter & Separation Techniques
Solution
Brass is a mixture of
A
Cu and Sn
B
Cu and Zn
C
Cu and Mg
D
Cu and Pb
medium Difficulty
Verified Correct Answer: Option B
Chemical Principles & Mechanism
Brass is an alloy made from copper and zinc. Unlike pure metals, most alloys do not have a single melting point, but a melting range in which the material is a mixture of solid and liquid phases.
Source: Myschool Past Questions Archive (Record #37818)
Chemistry
WAEC / WASSCE 2012
Acids, Bases, and Salts
Solution
Which of the following substances is mainly responsible for the depletion of the ozone layer?
A
Oxgyen
B
Chlorofluorocarbon
C
Carbon (ll) oxide
D
Nitrogen (ll) oxide
medium Difficulty
Verified Correct Answer: Option B
Chemical Principles & Mechanism
Ozone depletion occurs when chlorofluorocarbons (CFCs) and halons—gases formerly found in aerosol spray cans and refrigerants—are released into the atmosphere
Source: Myschool Past Questions Archive (Record #37819)
Chemistry
WAEC / WASSCE 2012
Matter & Separation Techniques
Solution
Burette readings (initial and final) must be given to two decimal places. Volume of pipette used must also be recorded but no account of experimental procedure is required. All calculations must be done in your answer book.
A solution containing 6.22 g of an acid H\(_2\)Y per dm\(^3\)
B contains 3.90 g of NaOH per dm\(^3\) of solution.
(a) Put A into the burette and titrate it against 20.0 cm\(^3\) or 25.0 cm\(^3\) portions of B using methyl orange as indicator. Repeat the titration to obtain consistent titres. Tabulate your burette readings and calculate the average volume of acid A used. The equation for the reaction involved in the titration is:
H\(_2\)\(_{(aq)}\) + 2NaOH\(_({aq})\) \(\to\) NaY\(_{(aq)}\) + 2H\(_2\)O\(_{(l)}\)
[H = 1.00; O = 16.0; Na = 23.0]
(b) From your results and the information provided above, calculate the:
(i) The concentration of B in moldm\(^{-3}\)
(ii) concentration of A in moldm\(^3\)
(ii) molar mass of H\(_2\)Y.
(c) State whether the pH of each of the following solutions is lower than 7, greater than 7 or equal to 7. The
(I) solution A before titration
(ii) solution B before titration
A
Oxgyen
B
Chlorofluorocarbon
C
Carbon (ll) oxide
D
Nitrogen (ll) oxide
medium Difficulty
Verified Correct Answer: Option B
Chemical Principles & Mechanism
ROUGH (cm\(^3\))
1st Titration (cm\(^3\))
2nd Titration (cm\(^3\)
Initial Burette Reading
27.00
49.50
36.00
Initial Burette Reading
01.00
26.00
12.40
Vol. of Acid Used(cm\(^3\))
26.00
23.50
23.60
Average Titre = \(\frac{23.50 + 23.60}{2}\) = 23.55cm\(^{3}\)
(b)(i) Concentration of B in moldm\(^{-3}\)
Molar mass of NaOH = 23 + 16 + 1 = 40g mol\(^{-1})
concentration of B = \(\frac{3.90}{40}\)
= 0.0975 mol dm\(^{-1}\)
(ii) concentration of BAin mol dm\(^{-3}\)
\(\frac{C_AV_A}{C_BV_B}\) = \(\frac{1}{2}\)
C\(_A = \frac{C_BV_B}{2V_A}\)
C\(_A\) = \(\frac{0.975 \times 25}{2 \times 23.55}\)
= 0.0518 mol dm\(^{-3}\)
(ii) Molar mass of H\(_2\)Y
Molar mas of H\(_2\)Y = \(\frac{6.22}{0.0518}\)
= 120 gmol\(^{-1}\)
(c)(i) Less than 7
(ii) Greater than 7
[C = (NH\(_4\))\(_2\)SO\(_{4(aq)}\); D = FeCl\(_{3(aq)}\)
Source: Official Exam / Past Question Archive
Chemistry
WAEC / WASSCE 2012
Matter & Separation Techniques
Solution
(a) (i) What is diffusion?
(ii) State Charles' law:
(iii) Sketch a graph to illustrate Charles' law.
(iv) A given mass of a gas occupied 150 cm3 at 27 ^\circC and a pressure of 1.013 x 105 Nm\(^{-2}\). Calculate the temperature at which its volume will be doubled at the same pressure.
(v) Arrange the three states of matter in order of increasing: (i) kinetic energy; (ii) forces of cohesion.
(b) (i) State Le Chatelier's principle. (ii) A metal M forms two oxides containing 11.1% and 20.0% of oxygen. Show that these figures agree with the law of multiple proportion.
(c) The table below shows the physical properties of substances A, B and C.
Substance
Melting point/^\circC
Boiling point/^\circC
Solubility in water at 25^\circC
A
30
117
Insolube
B
31
160
Insoluble
C
1200
1200
Insoluble
(i) If A and B are miscible when melted and B and C react when heated, describe how a mixture of A, B, and C could be separated.
(ii) When 25.25g of the mixture A, B and C was separated, 7.52 g of A and 8.48 g of B were recovered. Assuming i there was no loss of components during separation, calculate the percentage by mass of C in the mixture
medium Difficulty
Verified Correct Answer: Option
Chemical Principles & Mechanism
(a)(i) Diffusion is the movement of particles from the region of higher concentration to the region of lower concentration
(ii) Charles' Law states that the volume of a given mass of gas is directly proportional to its absolute temperature at a constant pressure.
(iii)
OR
(iv) \(\frac{V_1}{T_1} = \frac{V_2}{T_2}\) \(T_2 = \frac{T_1V_2}{V_1}\)
\(T_2 = \frac{300 \times 300}{150} = 600k\)
(v)(i) Solid < liquid < gas / solid, liquid, gas
(ii) Gas < liquid < Solid / gas, liquid, solid
b)(i) In a reversible reaction at equilibrium, if any will of the factors affecting the equilibrium is altered, the position of equilibrium will change so as to annul the effect of the change
(ii) Oxide I
% of O\(_2\) = 11.1 %
% by mass of metal = 88.9%
11.1 of O\(_2\) combined with 88.9 of metal
100 of O\(_2\) = \(\frac{100}{88.9}\) = 800.9g
Oxide II
% of O\(_2\) = 20%
% by mass of metal = 80%
20 of O\(_2\) combined with 80 of metal
100 of O\(_2\) = \(\frac{100}{ 80}\) = 400g
Ratio of metal in both oxides = 800. 9 : 400
2 : 1
(c)(i) Add water to mixture A, B and C and stir.
— C dissolves
— Filter to obtain C as filtrate and A and B as residue
— Heat residue until melted.
— Separate by simple distillation
— Evaporate filtrate to dryness to obtain solid C
— Pure A is collected at 117^\circC and pure B at 160^\circC
(ii) Mass of mixture = 25.25g
Mass A + B = 7.52g + 8.48g
= 16.00g
Mass of C = 25.25 - 16.00g
= 9.25g
% of C in mixture = \(\frac{9.25}{25.25}\) x 100
= 36.6%
Source: Myschool Past Questions Archive (Record #51711)
Chemistry
WAEC / WASSCE 2012
Matter & Separation Techniques
Solution
(a) (i) Define nuclear fission.
(ii) A certain natural decay series starts with \(^{238}_{92}U\) and ends with\(^{230}_{90}Th\). Each step involves the loss of an alpha or a beta particle. Using the given information, deduce how many alpha beta particpes were emitted.
(b) Consider the equilibrium reaction represented by the following equation:
A\(_{2(9)}\) + 3B\(_{2(9)}\) \(\rightleftharpoons\) 2AB\(_{3(g)}\); \(\Delta\)H = + xkJmol\(^{-1}\)
Explain briefly the effect of each of the following changes on the equilibrium composition: (i) increase in concentrat of B; (ii) decrease in pressure of the system; (iii) addition of catalyst.
(c) The lattice energies of three sodium halides are as follows:
Compound
NaF
NaBr
Nal
Lattice energy/kJmol\(^{-1}\)
890
719
670
Explain briefly the trend.
(d) State the property exhibited by nitrogen (IV) oxide in each of the following reactions:
(i) 4Cu + 2NO\(_2\) \(\to\) 4CuO + N\(_2\);
(ii) H\(_2\)O + 2NO\(_2\) \(\to\) HNO\(_3\) + HNO\(_2\).
(e) Iron is manufacturcd in a blast furnace using iron ore (Fe\(_2\)O\(_3\)), coke and limestone. Write the equation for the reaction(s) at the: (i) top of the furnace; (ii) middle of the furnace; (iii) bottom of the furnace.
(f) (i) Name two products of destructive distillation of coal. (ii) Give one use of each product in (f)(i).
medium Difficulty
Verified Correct Answer: Option
Chemical Principles & Mechanism
(a)(i) It is the splitting of a heavy nucleus into smaller nuclei accompanied by the release of large amount of energy.
(ii)\(^{238}_{92}U\) and ends with\(^{230}_{90}Th\) + \(2^{4}_{2}He\) + \(2^{o}_{-1e}Th\)
\(\alpha\) [articles = 2
\(\beta\) particles = 2
(b)(i) Equilibrium positicn shifts to the right and more of AB\(_3\) is formed or decrease in concentration of A\(_2\)
(ii) Equilibrium shifts to the left and more of A\(_2\) and; B\(_2\) formed / decrease in concentration of AB\(_3\)
(iii) No effect. Catalyst affects both forward and backward reactions equally.
(c) For a constant cation Na\(^+\) lattice energy decreases with ircreases in size of the anion / decrease in electronegativity of the anion.
F\(^-\), Br\(^-\), I\(^-\) increasing order of size. Hence the decreasing crder ofilattice energy.
(d)(i) NO\(_2\) is an oxidizing agent
(ii) NO\(_2\) is acting as an oxidizing as well as reducing agents OR acid anhydride.
(e)(i) Fe\(_2\) O\(_3\) + 3CO --> 2Fe + 3CO\(_2\)
(ii) CaCO\(_3\) —› CaO + CO\(_2\), CaO + SiO\(_2\) \(\to\) CaSiO3
(iii) C + O\(_2\) —> CO\(_2\), CO\(_2\) + C \(\to\) 2CO
(f) Coke I Coal Tar / Coal Gas /Ammonical Liquor
(ii) Coke — Solid fuels I production of water gas, extraction of ME Coal Tar — Synthesis of chemicals — perfumes, dyes, paints, drugs, plastic and explosives, etc. Coal Gas — as fuels in homes and industries
Ammonical liquor — production of (NH\(_4\))\(_2\) SO\(_4\) for fertilizer
Source: Myschool Past Questions Archive (Record #51723)