All 50 questions from the Joint Admissions and Matriculation Board (JAMB) Chemistry 2009 Objective paper, with the correct answer and a full explanation for each. Free, no signup needed.
A mixture of sugar and sulphur can be separated by
A. dissolution in water, evaporation and filtration
B. filtration, evaporation and dissolution in water
C. dissolution in water, filtration and evaporationCorrect
D. evaporation, dissolution in water and filtration
Explanation
Water should be added to the mixture. Since sugar is soluble in water while sulphur is not, the sugar remains in solution while sulphur is filtered off. The sugar is recovered from the solution by evaporation.
Freezing ice-cream is a physical change while dissolution of calcium in water, burning of kerosene and exposure of white phosphorous to air are chemical changes.
0.0075 mole of calcium trioxocarbonate (IV) is added to 0.015 mole of a solution of hydrochloric acid. The volume of gas evolved at s.t.p. is
A. 224cm3
B. 168cm3
C. 112cm3Correct
D. 100cm3
Explanation
CaCO3(s)+2HCl(aq)->CaCl2(aq)+H2O(l)+CO2(g). 1 mole of CaCO3 requires 2 moles of HCl. Thus, 0.0075mol of CaCO3 will take 0.0075x2=0.015mol of HCl. Since there is no limiting reagent, we can therefore use either of the two reagents to determine the volume of CO2 produced. 1 mole of CaCO3 produces 1 mole of CO2. Thus, mole of CO2 = 0.0075mol. Volume of CO2 = mole x G.M.V = (0.0075 x 22.4)dm3 = 0.168dm3 = 168cm3.
A. the molecules of a gas collide with the walls of the containerCorrect
B. some of the molecules are moving faster than others
C. of the collisions of the molecules with each other
D. of the mass of the molecules of the gas
Explanation
A gas exerts pressure on its container because the molecules of the gas collide with the walls of the container as the molecules are moving faster than others and of the collisions of the molecules with each other.
The basic assumption in the kinetic theory of gases that the collisions of the gaseous molecules are perfectly elastic implies that
A. the forces of attraction and repulsion are in equilibrium
B. gaseous molecules can occupy any available space
C. gaseous molecules will continue their motion indefinitelyCorrect
D. gases can be compressed
Explanation
During an elastic collision, both the momentum and kinetic energy are conserved. Since the kinetic energy is not decreasing, it implies that the motion will continue indefinitely.
If an atom is represented as X, which of the following deductions is correct?
A. It contains 12 protons
B. It forms a covalent chloride
C. Its atomic number is 23
D. It is an alkali metalCorrect
Explanation
X has (i) an atomic number of 11 (ii) a mass number of 23 (iii) 11 protons (iv) 11 electrons (v) 23-11=12 neutrons. Since it has 11 electrons, the structure is 2,8,1. Thus, it is a group 1 metal. Group 1 metals are also called alkali metals.
The azimuthal quantum number divides shells into orbitals. The quantum number is also known as
A. angular, secondary, subsidiary or sommerfield's quantum numberCorrect
B. principal quantum number
C. magnetic quantum number
D. spin quantum number
Explanation
The azimuthal quantum number divides shells into orbitals. The quantum number is also known as angular, secondary, subsidiary or sommerfield's quantum number.
The bond holding the components of a complex ion together is
A. coordinate bondCorrect
B. ionic bond
C. metallic bond
D. hydrogen bond
Explanation
The bond holding the components of a complex ion together is coordinate bond. [Cu(NH3)4]2+ is a complex ion. Coordinate bond is also known as dative bon(d).
The process by which a compound loses its water of crystallization to the atmosphere is known as
A. deliquescence
B. efflorescenceCorrect
C. hygroscopy
D. effervescence
Explanation
The process by which a compound loses its water of crystallization to the atmosphere is known as efflorescence. Examples of efflorescent compounds are Na2CO3.10H2O, CaCl2.2H2O, MgSO4.7H2O etc.
Which of the following statements is correct regarding the products of combustion, neutralization and electrolysis of water-related reactions?
A. The products of combustion of hydrocarbon are CO2 and H2O; the products of neutralization of an acid by a base are salt and water; the products of electrolysis of brine are hydrogen at the cathode and chlorine at the anode; the only product obtained during the combustion of hydrogen is waterCorrect
B. —
C. —
D. —
Explanation
The products of combustion of hydrocarbon are CO2 and H2O. The products of the neutralization of an acid by a base are salt and water. The products of the electrolysis of brine are hydrogen (at the cathode) and chlorine (at the anode). The only product obtained during the combustion of hydrogen is water: 2H2+O2->2H2O.
If 10.5g of lead (II)trioxonitrate (V) is dissolved in 20cm3 of distilled water at 18C, the solution of the solute in mol dm-3 is
A. 1.60Correct
B. 5.25
C. 16.00
D. 525.00
Explanation
Mass of Pb(NO3)2 = 10.5g. Molar mass of Pb(NO3)2 = 331g/mol-1. Mole of Pb(NO3)2 = 10.5g/331g/mol = 0.03172mol. Volume of distilled water = 20cm3 = (20/1000)dm3 = 1.586moldm-3 = 1.6moldm-3 [Pb=207, N=14, O=16].
Copper is commercially purified by electrolysis. The impure copper is made the
A. anode while pure copper is made the cathodeCorrect
B. cathode while pure copper is made the anode
C. anode and pure copper is also the anode
D. cathode and pure copper is also the cathode
Explanation
Copper is commercially purified by electrolysis. The impure copper is made the anode while pure copper is made the cathode. The anode progressively dissolves and the copper content is deposited on the copper cathode.
C(s)+H2O(g) -> H2(g)+CO(g), delta G for the reaction above at 1300K is -43kJ. At this temperature, the reaction is
A. not feasible
B. feasibleCorrect
C. —
D. —
Explanation
Since delta G is negative, the reaction is feasible (spontaneous). A positive delta G means that reaction is not feasible. If delta G equals 0, the reaction is at equilibrium.
Two equal bulbs, one containing ammonia and the other nitrogen, are opened mouth-to-mouth to each other at room temperature. The entropy in the mixture of gases is likely to
A. remain unchanged
B. increaseCorrect
C. decrease
D. change
Explanation
When gases are mixed (and the gases do not react), it is certain that the likelihood of finding a particular gas molecules in its original position will decrease i.e. the entropy (disorder) will increase.
The forward reaction of an endothermic reaction can be favoured by an increase in temperature. Thus, the reverse direction will require a decrease in temperature
A. TrueCorrect
B. False
C. —
D. —
Explanation
The forward reaction of an endothermic reaction can be favoured by an increase in temperature. Thus, the reverse direction will require a decrease in temperature. Also, since the forward reaction is associated with an increase in volume, it will be favoured by a decrease in pressure. Thus, the reverse direction will be favoured by an increase in pressure.
Ammonia reacts with excess air, in the presence of heated platinum as a catalyst, to produce nitrogen (ii) oxide and water
A. TrueCorrect
B. False
C. —
D. —
Explanation
4NH3(g) + 5O2(g) -> 6H2O(l) + 4NO(g). Ammonia reacts with excess air, in the presence of heated platinum as a catalyst, to produce nitrogen (ii) oxide and water.
Copper dissolves in Conc. HNO3 to liberate NO2 gas. It must be noted that NO is produced if the acid is dilute
A. TrueCorrect
B. False
C. —
D. —
Explanation
Cu+4HNO3->Cu(NO3)2+2H2O+2NO2 (Conc. Acid). 3Cu+8HNO3->3Cu(NO3)2+4H2O+2NO (dilute acid). Copper dissolves in Conc. HNO3 to liberate NO2 gas; NO is produced if the acid is dilute.
