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Chemistry
WAEC / WASSCE 2012
Matter & Separation Techniques
Solution
(a) (i) What is a structural isomer?
(ii) Write all the structural isomeric alkanols with the molecular formula C\(_4\)H\(_{10}\)O.
(iii) Which of the isomers from (a)(ii) above does not react easily on heating with acidified K\(_2\)Cr\(_2\)O\(_7\)?
(b) Chlorine reacted with excessentane in the presence of light. Chloropentane and a gas which fumes on cont with air were produced.
(i) Write an equation for the reaction.
(ii) Draw the structure of the major product.
(iii) What is the role of light in the reaction?
(iv) If a mixture of pentane and the major product is heated, which compounc would distil off first? Give a reason for your answer.
(v) Write the formula of the main product that would have be formed if but -1-ene has been used instead of pentane.
(c) Give the name and structural formula of the product which would be formed by hydration of each of the followinc compounds:
(i) CH\(_3\)CH(CH\(_3\))CH=CH\(_2\); (ii) CH\(_2\)=CHCOOH.
(d) (i) Write the structure of the amino acid, CH\(_3\)CH(NH\(_2\))COOH in: I. acidic medium; II. alkaline medium.
(ii) On analysis, an ammonium salt cf an alkanoic acid gave 60.5% carbon and 6.5% hydrogen. If 0.309 g of the salt yielded 0.0313 g of nitrogen, determine the empirical formula cf the salt. [H = 1.00; C =12.0; N =14.0; O = 16.0]
medium Difficulty
Verified Correct Answer: Option
Chemical Principles & Mechanism
(a)(i) Structural isomers are compounds with the same molecular formula but different arrangement of constituent at / or different structures
(ii) CH\(_3\) CH\(_2\) CH\(_2\) CH\(_2\) OH
(b)(i) C\(_5\)H\(_{12}\) + C\(_2\) \(to\) C\(_5\) H\(_{11}\)CI + HCI
(ii)
(iii) Light act as catalyst
(iv) Pentane C\(_2\)H\(_{12}\) would come out first Pentane has a lower molar mass (72) as compared to chloropentane (C\(_5\)H\(_{12}\)CI) (86.5) Hence weaker inter- molecular forces — van der waals' forces
(V) C\(_4\)\(H_8\)CI\(_{12}\)
(c)(i)
(ii)
(d)(i)
(ii) %N = \(\frac{0.0313}{ 0.309}\) x 100
= 10.1%
%0 = 100 — (60.5 + 6.5 + 10.1)
= 22.9
C; \(\frac{60.5}{12}\) H; \(\frac{6.5}{1}\) N; \(\frac{10.1}{14}\) O; \(\frac{22.9}{16}\)
C; \(\frac{5.04}{0.72}\) H; \(\frac{6.5}{0.72}\) N; \(\frac{0.72}{0.72}\) O; \(\frac{1.43}{0.72}\)
Empirical formula — C\(_7\)H\(_9\)NO\(_2\)
Source: Myschool Past Questions Archive (Record #51726)
Chemistry
WAEC / WASSCE 2012
Atomic Structure and Periodic Table
Solution
(a) (i) Define standard electrode potential.
(ii) State two factors that affect the value of standard electrode potential.
(iii) Give two uses of the values of standard electrode potential.
(iv) Draw and label a diagram for an electrochemic cell made up of Cu\(^{2+}\)/Cu; E^\circ = +0.34 V Zn\(^{2+}\)/Zn; E^\circ = -0.76 V
(v) Calculate the e.m.f. of the cell in (a)(iv) above.
(b) (i) In terms of electron transfer, define: I. oxidation; II. oxidizing agent.
(ii) Balance the following redox reaction: MnO\(^{-4}\) + l\(^{-}\) \(\to\) \(l_2\) + Mn\(^{2+}\)
(c) Classiify each of the following oxides as basic, amphoteric, acidic or neutral: (i) Carbon (II) oxide; (ii) Sulphu (IV) oxide; (iii) Aluminium oxide; (iv) Lithium oxide.
(d) What is hydrogen bonding?
medium Difficulty
Verified Correct Answer: Option
Chemical Principles & Mechanism
a)(i) It is a measure of the tendency of an element to form ions in solution relative to the tendency of hydrogen atoms to form ions in solution at standard conditions (at 298K and 1 atom and 1 molar concentration)
(ii) Concentration, Temperature, Pressure.
— To predict the direction/feasibility of a chemical reaction
— To calculate the e.m.f of a cell
— To predict the standard potential of unknown elements.
(v) = Emf = E^\circ(Right) — E^\circ(Left)
= + 0.34 — (— 0.76) V
= +1.10V
(b)(i) I Oxidation — a process of electron loss
II. Oxidizing agent—an electron acceptor
(ii) Separate into half reactions
(c) (i) Neutral (ii) Acidic (iii) Amphoteric (iv) Basic
(d) Hydrogen bonding is an intermolecular force between molecules in which hydrogen is attached to a very electronegative atom which has a small size, e.g. N, O, F.
Source: Myschool Past Questions Archive (Record #51727)
Chemistry
WAEC / WASSCE 2012
Matter & Separation Techniques
Solution
(a) Define each of the following terms: I. biotechnology; II. biogas.
(ii) State two applications of biotechnology
(b) (i) Describe briefly the production of ethanol from sugar cane juice.
(ii) State the by-product of the process in (b)(i)
(iii) Mention two uses of the by-product.
(iv) Ethanol can be produced from both cane sugar and petroleum. Explain briefly why the ethanol from cane sugar is renewable but that from petroleum is non-renewable.
(c) Distinguish between heavy chemicals and fine chemicals. Give one example of each chemical.
(d) Arrange the following gases in increasing order of deviation from ideal gas behaviour: HCl; O\(_2\); Cl\(_2\). Give reason(s) for your answer.
medium Difficulty
Verified Correct Answer: Option
Chemical Principles & Mechanism
(a)(i) I Biotechnology is the use of biological processes / living organisms to make products for human use.
II. Biogas is a fuel obtained from organic waste through the process of anaerobic decomposition
(ii) Production of drugs (medical), fertilizer, waste management, production of kenkey, fufu, gars, burukutu / any food or beverage produced from fermentation (domestic), industrial application, etc
(b)(i) — Add yeast to cane sugar and leave to stand (at room temperature)
— Enzyme sucrose hydrolyse / converts
— Enzyme zymase ferments / converts glucose to ethanol and CO\(_2\)
— Mixture is distilled to obtain ethanol.
ii) Carbon IV oxide
(iii) — In aerated drinks
— as fire extinguisher
— coolant / refrigerant
— solvay process
— synthesis of Na\(_2\)CO\(_3\)
iv) Ethanol from cane sugar is renewable because It is from plants which can be cultivated continuously Ethanol from petroleum is non-renewable because it is from a sou;-c,o, which can get exhausted. Heavy chemicals are chemicals used extensively in industries and are produced in very large quantities. Fine chemicals are chemicals produced in small quantities for specific purposes and to a very higil degree of purity. Heavy chemicals — H\(_2\)SO\(_4\), NaOH, NH\(_3\), CaCO\(_3\), HNO\(_3\), HCI, NaCO\(_3\) bleaching powder, metals (iron, tin, aluminium, Copper, Zinc).
Fine chemicals — laboratory / analytical reagents, drugs, dyes, perfumes, photographic reagents, additives, cosmetics.
d) O\(_2\), C\(_{12}\)HCI increasing order to deviation The extent of deviation depends on intermolecular forces. HCI is a polar and will have a greater intermolecular attraction than Oxygen and Chlorine. The molar mass of chlorine is greater than that of oxygen hence stronger van der waals forces than oxygen
Source: Myschool Past Questions Archive (Record #51728)
Chemistry
WAEC / WASSCE 2012
Atomic Structure and Periodic Table
Solution
(a) (i) What is the structure of the atom as proposed by Rutherford?
(ii) Distinguish between the atomic number and the mass number of an element.
(iii) Explain briefly why the relative atomic mass of chlorine is not a whole number.
(b) (i) What is meant by first ionization energy?
(ii) List three properties of electrovalent compounds.
(iii) Consider the following pairs of elements: I. \(_9\)F and \(_{17}\)Cl; \(_{12}\)Mg and \(_{20}\)Ca. Explain briefly why the elements in each pair have similar chemical properties.
(c) Explain briefly the following terms using an appropriate example in each case.
(i) homologous series; (ii) heterolytic fission.
(d) State the indicator(s) which could be used to determine the end-point of the following titrations:
(i) dilute hydrochloric acid against sodium hydroxide solution;
(ii) dilute hydrochloric acid against ammonium hydroxide solution;
(iii) ethanoic acid against sodium hydroxide solution.
(e) A solid chloride E which sublimed on heating reacted with an alkali F to give a choking gas G. G turned moist red litmus paper blue. identify E, F and G.
medium Difficulty
Verified Correct Answer: Option
Chemical Principles & Mechanism
(a)(i)The atom has small / tiny positively charged centre / nucleus with electrons surrounding the space around the centre nucleus.
(ii) Atomic number of an element is the number of protons / electrons in an atom of the element while mass number is the sum of the protons and neutrons in the atom of the element.
(iii) Chlorine atom is made up of a mixtire of isotopes and the relative atomic 'mass of chlorine is the average of the isotopic masses.
(b)(i) Is the minimum energy required to remove one mole of an electron from c mole of gaseous atom to form one mete gaseous ion. Nucleus with
— High melting / boiling point Protons Ability to conduct electricity in the molten state or in solution
— Solid at room temperature
— Soluble in water or polar solvents / insoluble in non-polar solvents.
(iii) — Atoms of the elements in each pair have the same number of electrons
(c)(i) It is a family of organic compounds their outermost shell therefore similar chemical properties. where successive members ditter by
— CH\(_2\) molar mass of 14
— with similar chemical properties
— which conform to the same general formula
— which show gradation of physical properties whict, have the same general method of preparation, e.g, alkanes, alkenes, alkanols.
(ii) It is a process in which a covalent bond is broken in such a way that the electron pair is completely transfered to one of the atoms resulting in the formation of ions e.g. H — CI —> H\(^+\) + Cl\(^-\) / HCI --> H\(^+\) + Cl\(^-\)
(d)(i) — Methyl orange / methyl red / phenolphthalein
(ii) — Methyl orange orange / methyl red
(iii) — Phenolphthalein.
(e) E — NH\(_4\)Cl
F — NaOH, KOH or Ca(OH)\(_2\), LiOH, CsOH, Ba(OH)\(_2\), Mg(OH)\(_2\)
G — NH\(_3\)
Source: Myschool Past Questions Archive (Record #51708)
Chemistry
WAEC / WASSCE 2012
Stoichiometry & Mole Concept
Solution
(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 (V) required to prepare 250 cm\(^3\) of 0.15gmoldm\(^3\) solution hydroxide is soluble. [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
medium Difficulty
Verified Correct Answer: Option
Chemical Principles & Mechanism
(a)(i) Lime water turns milky with CO\(_2\) because insoluble CaCO\(_3\) / CacO\(_{3(s)}\) is formed.
Milkiness disappears when excess CO\(_2\) reacts with CaCO\(_3\) in water medium forming the soluble Ca(HCO\(_3\)\(_2\))/Ca(HCO\(_3\))\(_2\)
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 OR Primary standard solution is a solution of known concentration prepared from pure / non - deliquescent / non hygroscopic substances.
(ii) Molar mass Na\(_2\)CO\(_3\) = 106gmol\(^{-1}\)
Molar mass Na\(_2\)CO\(_3\) = C x M x V
= 0.15 x 106 x 0.25
= 0.15 x 106 x 0.25
= 3.98g
Source: Myschool Past Questions Archive (Record #60012)
Chemistry
WAEC / WASSCE 2012
Matter & Separation Techniques
Solution
Credit will be given for strict adherence to the instructions, for observations precisely recorded, and for accurate inferences. All tests, observations, and inferences must be clearly entered in your answer book, in ink, at the time they are made.
C and D are two aqueous solutions. Carry out the following exercises on C and D. Record your observations and identify any gas(es) evolved. State the conclusion you draw from the result of each test.
(a)(i) To about 2 cm\(^3\) portion of C, add NaOH\(_{(aq)}\) In drops until in excess. Warm the mixture
(ii) To another 2 cm\(^3\) portion of C, add HCl\(_{(aq)}\) followed by BaCl\(_{2(aq)}\)
(b)(i) (ii) To another 2 cm\(^3\) portion of D, add add NH\(_{3(aq)}\) drops and then in excess.
(ii) To about 2 cm\(^3\) portion of D, add AgNO\(_{3(aq)}\) followed by HNO\(_{3(aq)}\)
medium Difficulty
Verified Correct Answer: Option
Chemical Principles & Mechanism
TEST
OBSERVATION
INFERENCE
(a)(i) C + NaOH\(_{(aq)}\) + warm
(ii) C + HCl\(_{(aq)}\) + BaCl\(_{2(aq)}\)
(b)(i) D + NH\(_{3(aq)}\)
(ii) D + AgNO\(_{3(aq)}\) + HNO\(^{3(aq)}\)
No visible reaction/no pot
A colourless gas with pungent/choking/irritating smell evolved.
Gas turned damp red litmus blue/formed white fumes with conc HCl vapour
No visible reaction while ppt formed
Reddish - brown/brown ppt
ppt insoluble
White ppt
ppt insoluble
Gas is NH\(_3\) from NH\(_4^+\)
SO\(_4^{2-}\) present
Fe\(^{3+}\) present
Cl\(^-\) or CO\(_3^{2-}\)
Cl\(^-\) present
Source: Myschool Past Questions Archive (Record #60013)
Chemistry
WAEC / WASSCE 2012
Stoichiometry & Mole Concept
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
medium Difficulty
Verified Correct Answer: Option
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: Myschool Past Questions Archive (Record #60014)
Chemistry
WAEC / WASSCE 2011
Basic Chemistry
Solution
The colour of phenolphthalein indicator in alkaline solution at the end-point of an acid-base titration is?
A
colourless
B
orange
C
pink
D
yellow
medium Difficulty
Verified Correct Answer: Option C
Chemical Principles & Mechanism
Phenolphthalein is one of the most commonly-used indicators in neutralisation titration.
Phenolphthalein is naturally colorless but turns pink in alkaline solutions.
Source: WAEC / JAMB / NECO Classroom Archive (Record #37613)
Chemistry
UTME / JAMB 2011
Acids, Bases, and Salts
Solution
Which of the following is a deliquescent compound?
A
NaNO3
B
CaCl2
C
CuO
D
Na2CO3.10H2O
medium Difficulty
Verified Correct Answer: Option B
Chemical Principles & Mechanism
Deliquescent substances are referred to known as those substances which absorbs moisture from the surrounding and dissolves themselves with the moisture or water to form a solution.
Examples are sodium hydroxide(NaOH), calcium chloride(CaCl2), potassium hydroxide(KOH), ammonium chloride(NH4Cl) , etc
Source: WAEC / JAMB / NECO Classroom Archive (Record #4779)
Chemistry
WAEC / WASSCE 2011
Periodic Table & Periodicity
Solution
Which of the following ions has the electron configuration 2,8,8?
A
Na+
B
Mg2+
C
F-
D
CI-
medium Difficulty
Verified Correct Answer: Option D
Chemical Principles & Mechanism
Chlorine(Cl) has configuration 2,8,7 but Chlorine ion (Cl-) has 18 electrons and configuration 2,8,8.
Here is the reason:
Chlorine has 17 electrons, and these are distributed in shells (or energy levels) as follows: 2 in the first shell, 8 in the second, and 7 in the third.This is represented as 2,8 7. Chlorine can gain one electron to achieve a stable electron configuration, resembling that of the noble gas Argon.
When chlorine gains an electron, its electron configuration becomes 2, 8, 8, making it a chloride ion (Cl⁻). The 2,8,8 configuration means the outermost shell is full with 8 electrons, which is the octet rule, making the ion stable.
Source: WAEC / JAMB / NECO Classroom Archive (Record #37554)
Chemistry
UTME / JAMB 2011
Matter & Separation Techniques
What is the concentration of a solution containing 2g of NaOH in 100cm3 of solution?
[Na = 23, O = 16, H = 1]
A
0.40 mol dm-3
B
0.50 mol dm-3
C
0.05 mol dm-3
D
0.30 mol dm-3
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 #4692)
Chemistry
UTME / JAMB 2011
Matter & Separation Techniques
Which of the following properties is NOT peculiar to matter?
A
kinetic energy of particles increase from solid to gas
B
Random motion of particles increases from liquid to gas
C
Orderliness of particles increases from gas to liquid
D
Random motion of particles increases from gas to solid
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 #4694)
Chemistry
UTME / JAMB 2011
Matter & Separation Techniques
Diagram
From the diagram above, an ideal can be represented by
Attached Figure / Diagram
A
M
B
N
C
K
D
L
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 #4696)
Chemistry
UTME / JAMB 2011
Atomic Structure and Periodic Table
Which of the following questions is correct about the periodic table?
A
The non-metallic properties of the elements tend to decrease across each period
B
The valence electrons of the elements increase progressively across the period
C
Elements in the same group have the same numbeer of electron shells
D
Elements in the same period have the number of valence electrons
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 #4697)
Chemistry
UTME / JAMB 2011
Stoichiometry & Mole Concept
Solution
The relative atomic mass of a naturally occurring lithium consisting of 90% \(^7 _3\)Li and \(^6 _3\)10% Li is
A
6.9
B
7.1
C
6.2
D
6.8
medium Difficulty
Verified Correct Answer: Option A
Chemical Principles & Mechanism
R.A.M = m\(_1 \alpha_1\) + m\(_2 \alpha_2\)
= 7(90/100) + 6(10/100)
= 6.3 + 0.6
= 6.9
Source: Myschool Past Questions Archive (Record #4698)