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Chemistry
NECO SSCE 2008
Atomic Structure, Orbitals & Nuclear Chemistry
If two elements X and Z with electronic configurations 2,8.3 and2,8,6 respectively combine, the compound formed will have the formula
A
XZ
B
XZ2
C
X2Z
D
X2Z3
E
X3Z2
medium Difficulty
Verified Correct Answer: Option D
Chemical Principles & Mechanism
No expanded working has been attached for this question yet. The verified answer is Option D.
Source: Myschool Past Questions Archive (Record #43569)
Chemistry
NECO SSCE 2008
Particulate Nature of Matter, Laws & Formulae
The following gases are diatomic EXCEPT
A
Fluorine
B
Helium
C
Hydrogen
D
Nitrogen
E
Oxygen
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 #43571)
Chemistry
NECO SSCE 2008
Acids, Bases, pH & Salts
Which of these is NOT a physical property f water?
A
Can be used to dissolve organic substances
B
Has a boiling point of 100 ° C
C
Has a density of 19cm3 at 40 °C
D
Has a freezing point of 0 ° C
E
is neutral to litmus
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 #43573)
Chemistry
NECO SSCE 2008
Electrolysis & Electrochemical Cells
During the electrolysis of sodium Chloride solution, hydrogen is discharged at the carbon cathode because
A
hydrogen ions are in greater concentration than sodium ions.
B
hydrogen is higher than sodium in the electrochemical series.
C
hydrogen is lower than sodium in the electrochemical series.
D
of the nature of the electrodes.
E
the concentration of sodium ions is greater than that of the hydrogen ion in the electrolyte.
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 #43575)
Chemistry
NECO SSCE 2008
Nature of Matter & Separation Techniques
Chromatography is used to separate components of mixtures which differ in their rates of
A
diffusion
B
migration
C
reaction
D
sedimentation
E
sublimation.
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 #43576)
Chemistry
NECO SSCE 2008
Electrolysis & Electrochemical Cells
Solution
The electrode potential in volts of 2H\(^+\)(aq) / H\(_2\)(q) system is
A
-2.87
B
-2.71
C
0.8
D
1.68
E
\( 0 \)
medium Difficulty
Verified Correct Answer: Option E
Chemical Principles & Mechanism
The electrode potential of 2H\(^+\)(aq) / H\(_2\)(q) system is defined as 0 volt. This is because the standard hydrogen electrode(SHE) is defined as the reference point of measuring electrode potentials, and it is assigned a value of 0 volts. The SHE consists of a platinum electrode immersed in a solution with a hydrogen ion concentration of 1 M, and bubbled with hydrogen gas at a pressure of 1 atm.
Source: Myschool Past Questions Archive (Record #43577)
Chemistry
NECO SSCE 2008
Water, Solutions & Solubility
A substance is said to be hygroscopic when it
A
absorbs atmospheric moisture and then goes into solution
B
absorbs atmospheric moisture but does not go into solution
C
changes colour
D
is not affected by atmospheric moisture
E
losses its water of crystallization
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 #43579)
Chemistry
NECO SSCE 2008
Chemical Energetics & Thermochemistry
Solution
A measure of the degree of disorderliness in a chemical system is known as the
A
activation energy
B
enthalpy
C
entropy
D
equilibrium
E
free energy.
medium Difficulty
Verified Correct Answer: Option C
Chemical Principles & Mechanism
Entropy is a measure of the randomness or disorder of a system. The value of entropy depends on the mass of a system. It is denoted by the letter S and has units of joules per kelvin.
Source: Myschool Past Questions Archive (Record #43581)
Chemistry
NECO SSCE 2008
Atomic Structure, Orbitals & Nuclear Chemistry
What is the maximum number of electrons that an f-orbital can accommodate?
A
2
B
6
C
7
D
10
E
14
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 #43582)
Chemistry
NECO SSCE 2008
Stoichiometry, Mole Concept & Volumetric Analysis
In which of these groups will all the substances be insoluble in water?
A
Na2CO3, KNO3,(NH4)2C03
B
NaHCO3, PbSO4, CaSO4
C
K2C03, CaSO4, AgNO3
D
PbCl2, NaCl, ZnCl2
E
ZnCO3, BaSO4,AgCl
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 #43585)
Chemistry
NECO SSCE 2008
Reaction Rates & Chemical Equilibrium
Solution
In which of the following equations can Le-chartelier’s principle be applied?
A
H2(g)+S(g) → H2(g)
B
2H2S(g) + O2 (g) → 2H2O(l) + 2SO2(g)
C
N2(g) +3H2(g)
⇌ 2NH3(g)
D
NaOH(aq) +CO2(g) → Na2CO3(aq) + H2O(l)
E
S(s) + 02(g) → SO2(g)
medium Difficulty
Verified Correct Answer: Option C
Chemical Principles & Mechanism
According to Le Chatelier's Principle, this will be favored if you lower the temperature. The system will respond by moving the position of equilibrium to counteract this - in other words by producing more heat. To get as much ammonia as possible in the equilibrium mixture, you need as low a temperature as possible
Source: Myschool Past Questions Archive (Record #43586)
Chemistry
WAEC / WASSCE 2008
Stoichiometry, Mole Concept & Volumetric Analysis
Solution
Burette readings(initial and final) must be given to two decimal places. Volume of pipette user must also be recorded but on account of experimental procedure is required. All calculations must be done in your answer book. A is O.050 mol dm\(^{-3}\) of acid HX. Bis a solution of NaOH containing 0.025 moles per 250 solutions.
(a) Put A into the burette and titrate it against 20.00 cm\(^3\) or 25.00 cm\(^3\) portions B using phenolphthalein as indicator. Tabulate your readings and calculate the average volume or A used.
(b) your results and the information provided above, calculate the;
(i) amount of acid in the average
(ii) amount of base in 20.00 cm\(^3\) or 25.00 cm\(^3\);
(iii) mole ratio of acid to base
(c) Write a balanced chemical equation for the reaction between the acid H\(_y\)X and the base NaOH
(d) State the basicity of the acid H\(_y\)X.
A
Brass
B
Bronze
C
Duralumin
D
Steel
medium Difficulty
Verified Correct Answer: Option B
Chemical Principles & Mechanism
Table of Result
Indicator used: Phenolphthalein
Volume of pipette = 25 cm\(^3\)
Burette Reading
Rough
1st
2nd
3rd
Final (cm\(^3\))
22.60
22.40
22.30
22.30
Initial (cm\(^3\))
0.00
0.00
0.00
0.00
Volume of acid used (cm\(^3\))
22.00
22.40
22.30
22.30
Average volume of acid used, V\(_A\) = \(\frac{22.40 + 22.30 + 22.30}{3}\)
= \(\frac{67.00}{3}\)
Average titre value = 22.30 cm\(^3\), V\(_A\)
(b)(i) Amount of acid in the average titre, V\(_A\)
1000 cm\(^3\) contains 0.05 moles
V\(_A\) will contain = \(\frac{0.05 \times 22.30}{1000}\)
= 0.0011 moles
(ii) Concentration of NaOH in B
\(\frac{0.025}{0.25}\) = 0.199 mol dm\(^{-3}\)
To calculate the amount of base in 25 cm\(^3\)
\(\frac{25 cm^3}{1000}\) x 0.100 mol dm\(^{-3}\) = 0.0025 moles
(iii) Mole ratio of acid (H\(_y\)X) to base (NaOH)
\(\frac{0.0011}{0.0025}\) = \(\frac{1}{2}\)
(c) Equation for the reaction
2NaOH + H\(_y\)X \(\to\) Na\(_2\)X + H\(_2\)O
(d) Basicity of acid H\(_y\)X = 2, (two)
Source: Official Exam / Past Question Archive
Chemistry
WAEC / WASSCE 2008
Atomic Structure, Orbitals & Nuclear Chemistry
Solution
(a) State (i) Pauli's Excusion principle;
(ii) Hund's rule of maximum multiplicity.
(b)(i) Write the electronic configuration of each of the following ions of copper: I. Cu\(_+\) II. Cu\(_{(2+)}\) [\(_{29}Cu\)]
(ii) Give the number of unpaired-electrons in each of the ions in (b)(i) above.
(iii) State the type of reaction represented by the following equation:
2Cu\(^+_{(aq)}\) \(\to\) Cu\(^{2+}_{(aq)}\) + Cu\(_{(s)}\)
(iv) Write the formula of one compound of Cu+.
(c)(i) Name the type of radiation that will I. penetrate lead block; II. be stopped by thin paper
(ii) Give the charge on each of the radiations mentioned in I(c)(i) above.
(iii) What term is used to describe each of the following nuclear processes?
I. Combination of two lighter nuclei to form a heavy nucleus II. Splitting of a heavy nucleus into two or more lighter nuclei
III. Time required for one-half of the atoms of a radioactive substance to decay.
(d) Arrange the following ions in order of increasing size. Give a reason for your answer in each case. I. Li\(^{+}\), K\(^{+}\), Na\(^{+}\); II. O\(^{2-}\), F\(^{-}\), N\(^{3-}\)
(e) Determine the percentage composition of phosphorus and oxygen in phosphorus (V) oxide [ P = 31, O = 16 ]
medium Difficulty
Verified Correct Answer: Option
Chemical Principles & Mechanism
(a)(i) State Pauli's exclusion principle: Pauli's exclusion principle states that two electrons in the same orbita of an atom cannot have same values for all four quantum numbers/no two electrons can have the same four quantum numbers/no two electrons in the same orbital if an atom can have the same spin.
(ii) Hund's rule of maximum multiplicity. Hund's rule states that electrons occupy each orbital supply first before pairinc takes place in degenerate orbital/most stable arrangement of electrons in sunshells is the one with the greatest number of parallel spins.
(b)(i) (a) Cu\(^+\) — 1s\(^2\)2s\(^2\)2P\(^6\)3P\(^6\)3d\(^{10}\)
(b) Cu\(^{2+}\) --- 1s\(^2\)2s\(^2\)2P\(^6\)3s\(^2\)3P\(^6\)3d\(^9\)
(ii) i. Cu\(^+\) — no unpaired electron
ii. Cu\(^{2+}\) — one unpaired electron
iii. Redox/disproportional
iv. Cu\(_2\)O / CuCI / Cu\(_2\)Cl\(_2\)
(c)(i) (a) gamma rays (b) alpha particles
(ii) (a) gamma (y) - No charge/electrically neutral. (b) alpha \(\alpha\)- positively charge.
(iii) (i) Nuclear fusion (2) Nuclear fusion (3) half-life.
(d) (i) Li\(^+\), Na\(^+\), K\(^+\), size increase down a group as more shells are being added.
(ii) F, O\(^{2-}\), N\(^{2-}\), size increase as nuclear charge decrease in the same period/isoelectronic.
(e) Phosphorus (V) oxide = \(P_4\)O\(_{10}\)/\(P_2\)\(Q_5\)
= (31 x 4) + (16 x 10) or (31 x 2) + (16 x 5) = 124 + 160 or 62 + 80 = 284 or 142.
Therefore % by mass of phosphorus = \(\frac{4P}{P_4Q_{10}}\) x 100% or
\(\frac{2P}{P_2Q_{5}}\) x 100%
\(\frac{124}{284}\) x 100% or \(\frac{62}{142}\) x 100%
= 43.7%
or 100 - 43.7 = 56.3% oxygen.
Source: Myschool Past Questions Archive (Record #52172)
Chemistry
WAEC / WASSCE 2008
Oxidation, Reduction & Redox Reactions
Solution
(a)(i) Define in terms of electron transfer I. oxidizing agent; II. reducing agent.
(ii) Write a balanced equation to show that carbon in a reducing agent.
(iii) State the change in oxidation number of the specie that reacted with carbon in (a)((ii).
(b) A gas X has a vapour density of 32. It reacts with sodium hydroxide solution to form salt and water only. It decolourizes acidified potassium tetraoxomanganate (VII) solution and reacts with H\(_2\)S to form sulphur. Using the information provided:
(i) identify gas X; (ii) state two properties exhibited by X;
(iii) give two uses of X.
(c) Consider the following substances: sodium; lead (II) iodide; hydrogen; magnesium; oxygen. Which of the substances
(i) conducts electricity?
(ii) is produced at the cathode during electrolysis of H\(_2\)SO\(_{4(aq)}\)?
(iii) corresponds to the molecular formula A\(_2\)?
(iv) is an alkaline earth metal?
d)(i) Define the term salt.
(ii) Mention two types of salt
(iii) Give an example of each of the salts mentioned in (d)(ii) above.
(e) In a neutralization reaction, dilute tetraoxosulphate (VI) acid completely reacted with sodium hydroxide solution.
(i) Write a balanced equation for the reaction
(ii) How many moles of sodium hydroxide would be required for the complete neutralization of 0.50 moles of tetraoxosulphate (VI) acid?
medium Difficulty
Verified Correct Answer: Option
Chemical Principles & Mechanism
(a)(i) (1) Oxidation agent is a substance which accepts electrons or is an electron acceptor.
(2) Reducing agent is a substance which donates electrons or is an electron donor.
(ii) 2CuO\(_{(s)}\) +C\(_{(s)}\) \(\to\) 2Cu\(_{(s)}\) + CO\(_{2(g)}\)
\(H_2\)O\(_{(g)}\) + C\(_{(s)}\) ----> CO\(_{(g)}\) + H\(_{2(g)}\)
CO\(_{2(g)}\) --> 2CO\(_{(g)}\)
(ii) Cu in CuO from +2 to 0
H in H\(_2\)O from +1 to 0
C in CO\(_2\) from +4 to + 2.
(b)(i) X is sulphur (IV) oxide or sulphur dioxide.
(ii)(a) It is heavier than air. (b) It is acidic
(c) Reducing or oxidizing agent.
(d) Colourless (poisonous) gas with irritating smell.
(iii) (1) Used for bleaching
(2) For the manufacture of H\(_2\)SO\(_4\)
(3) as germicide and fumigant.
(4) for preservation.
(5) as refrigerant.
(c) (i) sodium magnesium (ii) Hydrogen (iii) Lead(II) iodide (iv) Magnesium.
(d) (i) A salt is a compound formed when all or part of hydrogen of an acid is replaced by metal or ammonium ion.
(ii) (a) Normal salt (b) Acid salt (c) Basic salt (d) Double salt (e) Complex salt.
(iii) NaCl/ZnSO\(_4\)/NaH\(_2\)PO\(_4\)/Zn(OH)Cl/Mg(OH)NO\(_3\)/NH\(_4\).Fe(SO\(_4\))\(_2\).6H\(_2\)O).
(e) (I) H\(_2\)SO\(_{4(aq)}\) + 2NaOH\(_{(aq)}\) \(\to\) Na\(_2\)SO\(_4\)\(_{(aq)}\) + 2H\(_2\)O\(_{(l)}\)
(ii) From the reaction 1 mole of H\(_2\)SO\(_4\) = 2 moles of NaOH\(_{(l)}\).
Therefore 0.50 mole of H\(_2\)SO\(_4\) = \(\frac{2 \times 0.5}{1}\) of NaOH
= 1 mole of NaOH.
Source: Myschool Past Questions Archive (Record #52177)
Chemistry
WAEC / WASSCE 2008
Organic Chemistry II: Functional Groups, Polymers & Biomolecules
Solution
(a) Consider the following reaction sequence.
(i) What process leads/tathe formation of K?
(ii) Write the formula of K.
(iii) Write the structural formula of L and name L.
(iv) Name A\(_n\)
(v) Write the structure of M and name M.
(b)(i) What are carbohydrates?
(ii) Give one example each of a I. monosaccharide; II. disaccharide; III. polysaccharide.
(c) Consider the following structure of a simple sugar :
(i) Which functional group makes the compound a reducing agent?
(ii) State what would C = O be observed when I. the compound is mixed with Fehling's solution and boiled;
I. few drops of concentrated H\(_2\)SO\(_4\) is added to the sample of the compound. H—C—OH
(iii) Write an equation for the reaction in (c)(ii)(II).
(d) A hydrocarbon Z with molecular mass 78 on combustion gave 3.385 g of CO\(_2\) and and 0.692 g of H\(_2\)O. Determine the molecular formula of Z. [ H = 1, C = 12, O = 16]
medium Difficulty
Verified Correct Answer: Option
Chemical Principles & Mechanism
(a)(i) Dehydration
(ii) C\(_2H_4\)
(iii)
(iv) Polythene/Polythene
(b)(i) Carbohydrates are (naturally occurring) organic compounds containing carbon, hydrogen and oxygen with the hydrogen and oxygen present in the ratio of 2:1 (as in water).
(ii)1. Monosaccharide : glucose/fructose 2. Disaccharide: sucrose/lactose/maltose. 3. Polysaccharide : starch/glycogen/cellulose.
(c)(i)
(I) (a) brick red precipitate (b) black/charred mass (of carbon is observed).
(iii) C\(_6\)H\(_{12}\)O\(_6\) \(\to\) 6C + 6H\(_2\)O
(d) Mass of hydrogen in Z = \(\frac{12}{8 \times 0.692}\) = 0.077g
Mass of carbon in Z = \(\frac{12}{44}\) x 3.385 = 0.923g.
C H
0.923 0.077
12 1
0.077 0.077
0.077 0.077
0.077 0.077
Empirical formula of Z = CH
(CH)\(_n\) = 78
13\(_n\) = 78
n = \(\frac{78}{13}\)
= 6
molecular formula of Z = C\(_6\)H\(_{16}\)
Source: Myschool Past Questions Archive (Record #52178)