Chemistry 2005 Jamb Examination
Question 21
The solubility curve shows the variation of solute concentration with
Smelting is a process of applying heat and a chemical reducing agents to an ore to extract a desired product.
The reducing agent is commonly a fossil-fuel source of carbon, such as carbon monoxide from incomplete combustion of coke. The oxygen in the ore binds to carbon at high temperatures, as the chemical potential energy of the bonds in carbon dioxide (CO2) is lower than that of the bonds in the ore. The main industrial uses include fossil fuel processing and ammonia production. Emerging uses for hydrogen include the use of fuel cells to generate electricity
Sulphide ores such as those commonly used to obtain copper, zinc or lead, are roasted before smelting in order to convert the sulphides to oxides, which are more readily reduced to the metal. Roasting heats the ore in the presence of oxygen from air, oxidizing the ore and liberating the sulphur as SO2 gas.
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Question 22
Kerosene is commonly used to remove the red colour stain of palm oil from cloths because if
C. Makes the oil evaporate easily by dissolving it
Kerosene is a non-polar solvent that dissolves the palm oil allowing it to be lifted from the fabric, making subsequent cleaning effective.
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Question 23
The gas that is the most dangerous pollutant to human is
D. Hydrogen sulphide (H2S)
H2S is highly toxic even at low concentrations and can rapidly cause respiratory paralysis; it is therefore especially dangerous compared with the other listed gases.
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Question 24
Natural water collected from rivers and ponds contain oxygen, carbon (IV) oxide and
A. Nitrogen
Natural water dissolves gases from the atmosphere — dissolved oxygen and CO2 are common, and nitrogen (N2) is also present in solution.
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Question 25
How many moles of limestone will be required to produce 5.6g of CaO?
[Ca = 40, C = 12, O= 16]
B. 0.10 mol
Molar mass of CaO = 40 + 16 = 56 g·mol−1. Moles of CaO formed:
\[ n=\dfrac{5.6\ \text{g}}{56\ \text{g·mol}^{-1}}=0.10\ \text{mol} \]
Since CaCO3 → CaO + CO2 is 1:1, 0.10 mol of CaCO3 is required.
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Question 26
D. Tetrahedral
CH4 (methane) has four bonding pairs arranged tetrahedrally around carbon (VSEPR) giving bond angles ≈109.5°.
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Question 27
A. Strong intermolecular attraction
Solids have particles held in fixed positions by strong intermolecular (or interatomic) forces, which gives them a definite shape.
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Question 28
B. Crystallization
Sugar is separated and purified by crystallization — the sugar crystallizes out leaving soluble impurities in the mother liquor.
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Question 29
D. Electron
Electrons have very small mass compared with protons and neutrons, so they contribute least to the mass of an atom.
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Question 30
An element will readily form an electrovalent compound if its electron configuration is
A. 2, 8, 1
An element with configuration 2,8,1 (one valence electron) readily loses that electron to form a cation and thus forms electrovalent compounds easily.
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