All 20 questions from the Post-UTME Screening (Post-UTME) Chemistry 2015 Objective paper, with the correct answer and a full explanation for each. Free, no signup needed.
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Which of the following solids has a giant (macromolecular) structure?
Diamond has a giant covalent (macromolecular) lattice structure, unlike the simple molecular structures of iodine and sulphur.
The following gases decolourize bromine water except
C2H6 (ethane) is a saturated alkane and does not decolourize bromine water; the others are unsaturated and do.
The alloy used for metal work and contains
Bronze, an alloy of copper and tin, is commonly used for metalwork and casting.
The components of a universal indicator solution can best be separated/prepared by
Chromatography separates the different coloured dye components of a universal indicator solution.
The oxidation number of phosphorus in PO4^3- is
In the phosphate ion PO4^3-, oxygen is -2 (x4=-8); for overall charge -3, P must be +5.
Water can be obtained as the only product by
2H2 + O2 -> 2H2O; burning hydrogen in oxygen produces only water as a product.
The oxidation of ammonia in excess oxygen (catalytic oxidation) produces
Catalytic oxidation of ammonia (the first stage of the Ostwald process for nitric acid) produces nitrogen monoxide, NO.
The gasification of coke is used in the manufacture of
Passing air/steam over hot coke (gasification) produces producer gas, a mixture of CO, CO2, N2 and H2.
The synthetic equivalent of natural rubber is a polymer of
Synthetic rubber (e.g. polybutadiene) is typically made by polymerizing buta-1,3-diene.
The addition of concentrated sodium chloride solution during the manufacture of soap is to
Adding concentrated brine ('salting out') reduces the solubility of soap, causing it to precipitate out of solution for easy separation.
The equation which illustrates the oxidizing property of Sulphur (IV) oxide is
In this reaction, SO2 is reduced (S goes from +4 to 0) while oxidising H2S (S from -2 to 0), demonstrating its role as an oxidizing agent.
When chlorine gas is passed into potassium iodide solution, iodide is set free through the process of
Chlorine displaces the less reactive iodine from potassium iodide, a halogen displacement reaction.
2H2O(l) + X2(g) <=> H2O2(aq) + 2HX(aq). X in the reaction above is
This reaction, where a halogen reacts with water to produce hydrogen peroxide and a hydrogen halide, is characteristic of fluorine, the most reactive halogen.
The process in which coal is heated above 500C in the absence of air is referred to as
Heating coal strongly in the absence of air to break it down into useful products is called destructive distillation.
In the electrolytic extraction of aluminum from bauxite, carbon anodes are changed at intervals because they
The carbon anodes are gradually burnt away as they react with the oxygen liberated during electrolysis, forming CO2, and must be replaced periodically.
Paramagnetism in transition metal ions is due to the presence of
Paramagnetism arises from the presence of unpaired electrons in the d-orbitals of transition metal ions.
Stainless steel is an alloy of
Stainless steel is an alloy of iron, chromium, nickel and a small amount of carbon.
The major constituents of cement are
The major constituents of cement are calcium silicates and calcium aluminate.
The type of iron obtained directly from the blast furnace is
Iron obtained directly from the blast furnace is known as pig iron.
If a sample of fructose C6H12O6 contains 24g of carbon, calculate the mass of oxygen in it. [C=12, H=1, O=16]
Moles of C = 24/12 = 2mol. Since fructose has 6 C and 6 O atoms per molecule, moles of fructose = 2/6 = 1/3 mol, so moles of O = 6 x 1/3 = 2mol. Mass of O = 2 x 16 = 32g.
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