All 50 questions from the Joint Admissions and Matriculation Board (JAMB) Chemistry 2007 Objective paper, with the correct answer and a full explanation for each. Free, no signup needed.
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A mixture of petrol and water can be separated through
Petrol and water are immiscible liquids, so they can be separated using a separating funnel.
MnO2(s) + xHCl(aq) -> MnCl2(aq) + yH2O(l) + zCl2(g). In the equation above, what are the values of x, y and z respectively?
The balanced equation is MnO2 + 4HCl -> MnCl2 + 2H2O + Cl2, so x=4, y=2, z=1.
What is the volume of oxygen required to burn completely 45cm3 of methane at s.t.p?
CH4 + 2O2 -> CO2 + 2H2O. Volume ratio CH4:O2 = 1:2, so O2 required = 2 x 45cm3 = 90.0cm3.
Which of the following decreases when a given mass of gas is compressed to half its initial volume?
Compressing a gas forces its molecules closer together, so the average distance between molecules decreases.
Calculate the mass of chlorine gas which occupies a volume of 1.12dm3 at s.t.p. [Cl=35.5, Molar volume of a gas at s.t.p = 22.4dm3]
Moles of Cl2 = 1.12/22.4 = 0.05mol. Molar mass Cl2 = 71g/mol. Mass = 0.05 x 71 = 3.55g.
A metal X forms two bromides with the formulae XBr2 and XBr3. What type of bonding exists between X and bromine in the bromides?
X shows variable oxidation states (+2 and +3), indicating it is a transition metal. Bonding between a metal (X) and a non-metal (bromine) is ionic.
How many electrons are in the L shell of P?
Phosphorus (Z=15) has electron structure 2,8,5 (K,L,M). The L shell (second shell) contains 8 electrons.
Which experiment led to the measurement of the charge on an electron?
R. A. Millikan's oil-drop experiment measured the charge on an electron as -1.6 x 10^-19 C.
If the electron configuration of an element is 1s2 2s2 2p5, how many unpaired electrons are there?
In the 2p5 sub-shell, five of six available p-orbital slots are filled; drawing the orbital box diagram shows only one unpaired electron.
The elements that belong to the third period of the periodic table are
Na, Mg, S and Ar all have three electron shells, placing them in period 3.
The presence of nitrogen in air is to
Nitrogen is an inert diluent in air; it retards (slows down) both combustion and corrosion.
When temporary hard water is boiled for some time in a kettle, the inner surface of the kettle becomes coated with a deposit of
Boiling decomposes calcium hydrogencarbonate, Ca(HCO3)2 -> CaCO3 + H2O + CO2, depositing insoluble calcium trioxocarbonate(IV) (limescale).
A good drying agent should be
Hygroscopic substances absorb moisture without dissolving in it, making them preferred as drying agents (unlike deliquescent substances, which dissolve).
What weight of NaCl is needed to make 2.0 dm3 of a 1.5M solution? [Na=23, Cl=35.5]
Moles = concentration x volume = 1.5 x 2.0 = 3.0mol. Molar mass NaCl = 58.5g/mol. Mass = 3.0 x 58.5 = 175.5g (~175g).
A supersaturated solution is said to contain
A supersaturated solution holds more dissolved solute than its normal solubility limit at that temperature, typically in the presence of undissolved excess solute.
Smog usually occurs over cities which
Smog is closely associated with air pollution from burning large quantities of fossil fuels.
Tartaric acid is used industrially to
Tartaric acid is used industrially in the manufacture of baking powder.
Calculate the number of moles of HCl present in 20cm3 of a 0.75M solution of acid.
Moles = concentration x volume(dm3) = 0.75 x 0.020 = 0.015 mole.
The salt formed from a strong acid and a strong base is
A salt formed by complete neutralization of a strong acid with a strong base is neutral (pH 7).
The reaction that takes place in a Daniell cell is
A Daniell cell operates via a redox (oxidation-reduction) reaction between zinc and copper.
The oxidation state of oxygen in tetraoxosulphate (VI) acid is
In H2SO4: (1x2)+6+4x=0 => 8+4x=0 => x=-2, the standard oxidation state of oxygen.
How long would it take to deposit 0.08g of copper from CuCl2 solution by passing a current of 0.5A? [Cu=64, F=96500 C/mol]
Cu2+ + 2e- -> Cu: 64g needs 2x96500C, so 0.08g needs (2x96500x0.08)/64 = 241.25C. t=Q/I=241.25/0.5=482.5s = about 8 minutes.
What happens when a zinc rod is immersed in copper (II) tetraoxosulphate(VI) solution?
Zinc, being higher in the electrochemical series, displaces copper: Zn + Cu2+ -> Zn2+ + Cu, so the blue Cu2+ colour fades as copper is deposited.
Dissolving some pellets of NaOH in water would result in
As NaOH dissolves, its ions disperse randomly through the water, increasing the disorder (entropy) of the system.
C2H4(g) + H2(g) -> C2H6(g), delta H = -137kJ/mol. The reaction represented above is
A negative delta H indicates heat is released, characteristic of an exothermic reaction.
Use the diagram (potential energy vs reaction coordinate, catalyzed and uncatalyzed curves) below to answer questions 26. In the diagram, the respective activation energies for the catalyzed and uncatalyzed reactions in kJ are
Reading the peaks of the two curves on the diagram, the uncatalyzed reaction has a higher activation energy (50kJ) than the catalyzed reaction (45kJ).
Na2S2O3(aq) + 2HCl(aq) -> 2NaCl(aq) + H2O(l) + SO2 + S(s). Which of the following would increase the rate of the chemical reaction above?
Both raising temperature and raising reactant concentration independently speed up reactions; together they synergistically increase the rate.
H3PO4(aq) + H2O(l) <=> H2PO4- + H3O+, delta H = -13kJ at 298K. In the reaction above, an increase in temperature would favour
Since the forward reaction is exothermic (delta H negative), raising temperature (Le Chatelier's principle) favours the endothermic reverse reaction.
Cu2+(aq) + 4NH3(aq) <=> [Cu(NH3)4]2+(aq). In the reaction above, what is the effect of removing/precipitating Cu2+ from the equilibrium?
Removing Cu2+ shifts the equilibrium backward (left) to replace it, releasing (generating) more free NH3.
A solution which on treatment with hydrochloric acid produces a colourless, odourless gas which turns lime water milky is most likely to be a
A carbonate reacting with HCl releases CO2 gas, which is colourless, odourless and turns limewater milky, e.g. CaCO3 + 2HCl -> CaCl2 + H2O + CO2.
Sulphur is used industrially in the production of
Sulphur is a key raw material used in the manufacture of matches (and matchboxes).
Use the diagram below (producer gas apparatus with coke, air inlet, and gas outlets L and M) to answer questions 32 and 33. The fuel gas labeled L is
In the producer-gas process, when steam (instead of air alone) is passed over hot coke, the fuel gas produced is water gas (a mixture of CO and H2).
The alternative raw material labeled M (used instead of air) is
Steam is used as the alternative raw material (instead of air) to produce water gas from hot coke.
Tincture of iodine means iodine dissolved in
Tincture of iodine is a solution of iodine dissolved in ethanol (alcohol).
If chlorine is bubbled into water and the resulting yellowish-green solution is exposed to bright sunlight for a while, the solution will decompose giving out
Chlorine water contains hypochlorous acid (HOCl), which decomposes in sunlight to release oxygen, leaving aqueous hydrochloric acid behind.
The reddish-brown rust on iron roofing sheets consists of
Rust is hydrated iron(III) oxide, with the formula Fe2O3.xH2O (commonly written Fe2O3.3H2O).
When calcium oxide is heated with carbon, the oxide will
Heating calcium oxide with carbon converts it to calcium carbide (CaC2).
Copper and silver metals are commonly used as coins because they are
Copper and silver are low in reactivity, so they resist oxidation and tarnishing, making them suitable for coins.
Which of the following sets of metals dissolves in dilute HCl?
Mg, Sn and Fe are all more reactive than hydrogen and dissolve in dilute HCl, whereas copper (below hydrogen in the reactivity series) does not.
The softer solder used for welding and plumbing is an alloy of
Soft solder used in welding/plumbing is traditionally an alloy of lead and tin.
The conversion of open chain alkanes into cycloalkanes and aromatic compounds is called
The IUPAC nomenclature of the compound C2H5CH2COOCH2CH3 is
The acid portion (C2H5CH2COOH) is butanoic acid and the alcohol portion (CH3CH2-) is ethyl, giving the ester name ethyl butanoate.
Which of the following compounds is a tertiary alkanol?
A tertiary alkanol has the carbon bearing the -OH group attached to three other alkyl groups; 2-methylbutan-2-ol fits this description.
CH3CH2Cl + KCN -> CH3CH2CN + KCl. In the reaction above, the cyanide ion is
The negatively charged cyanide ion (CN-) is attracted to the electron-deficient carbon and donates an electron pair, making it a nucleophile.
How many structural isomers of chlorobutane are possible?
Chlorobutane has four structural isomers: 1-chlorobutane, 2-chlorobutane, 1-chloro-2-methylpropane, and 2-chloro-2-methylpropane.
Certain useful waxes are composed mainly of
Natural waxes are largely composed of esters (alkanoates) of long-chain alcohols and fatty acids.
Which of the following compounds is the best possible anti-knock agent for petrol?
The more highly branched a hydrocarbon chain, the better its anti-knock (octane) rating; among the options, the most branched structure is the best anti-knock agent.
Which of the following represents an aromatic compound?
C6H5OH (phenol) contains a benzene ring and is a classic aromatic compound; the other formulas are not aromatic as written.
The hydrocarbon used in the production of styrene is
Styrene is manufactured from ethene (via ethylbenzene, reacted with benzene, then dehydrogenated).
Which of the following alkanes has the highest boiling point?
Boiling point increases with molecular mass/chain length in the alkane homologous series; pentane (C5H12) has the highest boiling point of those listed.
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