Chemistry 2010 Jamb Examination
Chemistry 2010 Jamb Examination
Question 21
Which of the following is used in rocket fuels?
Correct: A.
Concentrated nitric acid (HNO3) is commonly used as an oxidizer in some rocket propellants and in the manufacture of other energetic materials used in rocketry.
Concentrated nitric acid (HNO3) is commonly used as an oxidizer in some rocket propellants and in the manufacture of other energetic materials used in rocketry.
Not clear enough?
Question 22
A constituent common to bronze and solder is
Correct: D.
Bronze is primarily an alloy of copper and tin, while many traditional soft solders contain tin (often with lead or other metals). Tin is therefore a constituent common to both bronze and many solder formulations.
Bronze is primarily an alloy of copper and tin, while many traditional soft solders contain tin (often with lead or other metals). Tin is therefore a constituent common to both bronze and many solder formulations.
Not clear enough?
Question 23
Iron can be protected from corrosion by coating the surface with
Correct: D.
Galvanizing (coating iron or steel with zinc) protects iron from corrosion because zinc is more reactive and corrodes preferentially (sacrificial protection), and it also provides a protective barrier.
Galvanizing (coating iron or steel with zinc) protects iron from corrosion because zinc is more reactive and corrodes preferentially (sacrificial protection), and it also provides a protective barrier.
Not clear enough?
Question 24
What quantity of aluminium is deposited when a current of 10A is passed through a solution of an aluminium salt for 1930 s?
[Al = 27, F = 96500 C mol-1]
[Al = 27, F = 96500 C mol-1]
Correct: B.
Total charge passed: Q = I Ă— t = 10 A Ă— 1930 s = 19300 C.
Moles of electrons = Q / F = 19300 / 96500 = 0.200 mol e-.
Aluminium is deposited by the reaction Al3+ + 3e- → Al, so moles of Al = moles e- / 3 = 0.200 / 3 = 0.066666... mol.
Mass of Al = moles Ă— atomic mass = 0.066666... Ă— 27 = 1.8 g.
Total charge passed: Q = I Ă— t = 10 A Ă— 1930 s = 19300 C.
Moles of electrons = Q / F = 19300 / 96500 = 0.200 mol e-.
Aluminium is deposited by the reaction Al3+ + 3e- → Al, so moles of Al = moles e- / 3 = 0.200 / 3 = 0.066666... mol.
Mass of Al = moles Ă— atomic mass = 0.066666... Ă— 27 = 1.8 g.
Not clear enough?
Question 25
In which of the following is the entropy change positive?
Correct: A.
Thermal dissociation of ammonium chloride (solid → gaseous NH3 + HCl) increases the number of gaseous particles and disorder, so ΔS > 0.
Thermal dissociation of ammonium chloride (solid → gaseous NH3 + HCl) increases the number of gaseous particles and disorder, so ΔS > 0.
Not clear enough?
Question 26
If a reaction is exothermic and there is a great disorder, it means that
Correct: D.
Gibbs free energy ΔG = ΔH - TΔS. For an exothermic reaction ΔH is negative; if ΔS is large and positive (great disorder), then -TΔS is negative and large, so ΔG becomes much more negative — a large decrease in free energy.
Gibbs free energy ΔG = ΔH - TΔS. For an exothermic reaction ΔH is negative; if ΔS is large and positive (great disorder), then -TΔS is negative and large, so ΔG becomes much more negative — a large decrease in free energy.
Not clear enough?
Question 27
In the preparation of oxygen by heating KClO3 in the presence of MnO2, only moderate heat is needed because the catalyst acts by
Correct: D.
A catalyst provides an alternative reaction pathway with a lower activation energy (lowers the energy barrier), so less heat is required to achieve a useful rate of reaction.
A catalyst provides an alternative reaction pathway with a lower activation energy (lowers the energy barrier), so less heat is required to achieve a useful rate of reaction.
Not clear enough?
Question 28
Calculate the volume of 0.5 mol dm-3 H2SO4 that is neutralized by 25 cm3 of 0.1 mol dm-3 NaOH
Moles NaOH = concentration Ă— volume
= 0.1 mol·dm-3 × 25 cm3 × (1 dm3/1000 cm3)
= 0.1 Ă— 0.025 = 0.0025 mol.
Reaction: H2SO4 + 2 NaOH → Na2SO4 + 2 H2O, so moles H2SO4 required
= 0.0025 / 2 = 0.00125 mol.
Volume of 0.5 mol·dm-3 acid = moles / concentration
= 0.00125 / 0.5 = 0.0025 dm3 = 2.5 cm3.
= 0.1 mol·dm-3 × 25 cm3 × (1 dm3/1000 cm3)
= 0.1 Ă— 0.025 = 0.0025 mol.
Reaction: H2SO4 + 2 NaOH → Na2SO4 + 2 H2O, so moles H2SO4 required
= 0.0025 / 2 = 0.00125 mol.
Volume of 0.5 mol·dm-3 acid = moles / concentration
= 0.00125 / 0.5 = 0.0025 dm3 = 2.5 cm3.
Not clear enough?
Question 29
The colour of methyl orange in alkaline medium is
Methyl orange is yellow in alkaline (basic) solution and red in acidic solution; its transition range gives orange in between.
Not clear enough?
Question 30
Which of the following salts is slightly soluble in water?
Calcium sulfate (CaSO4) is only slightly soluble in water. Silver chloride (AgCl) and lead(II) chloride (PbCl2) are sparingly soluble, but in the context of 'slightly soluble' CaSO4 is commonly listed; sodium carbonate is soluble.
Not clear enough?
You might like
Choose from the letters labelled A – D the one that is related to the fifth word in the same way as the words of the first two pairs are related.
Midrib, bird; trolley, yell; cinema, _____
A siren having a ring of 200 hole makes 132 rev/min. A jet of air is directed on the set of holes. Calculate the frequency and wavelength in air of the note produced (take v = 350m/s)