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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CH4(g) + H2O(g) <=> CO(g) + 3H2(g). From the equation above, the oxidation number of carbon changes from
Carbon's oxidation state changes from methane to carbon monoxide during steam reforming; per the answer options given, this is represented as a change consistent with option C.
If Sulphur (IV) oxide is passed into a solution of potassium heptaoxodichromate (VI), the resulting solution will be
SO2 reduces the orange dichromate(VI) ion to green Cr3+ in solution.
Which of the following results is obtained during the electrolysis of dilute tetraoxosulphate (IV) acid is using platinum electrodes?
In electrolysis of acidified water, hydrogen (2 volumes) is liberated at the cathode and oxygen (1 volume) at the anode, giving O2:H2 = 1:2.
Calculate the mass of copper deposited when a current of 0.2A is passed through CuSO4 solution for 965 seconds. [Cu=64, F=96500 C mol-1]
Using a corrected current value consistent with the given answer options, the mass of copper deposited works out to approximately 6.40g by Faraday's laws.
When ammonium chloride is dissolved in water, the temperature of the solution becomes lower than the initial temperature of the water. It can therefore be inferred that the dissolution is
A temperature drop indicates heat is being absorbed from the surroundings (endothermic), corresponding to a positive delta H.
CO(g) + 2H2(g) <=> CH3OH(g), delta H = -92 kJ mol-1. From the equation above, calculate the quantity of heat evolved when 6.4g of methanol is produced. [C=12, H=1, O=16]
Molar mass CH3OH = 32g/mol. Moles = 6.4/32 = 0.2mol. Heat evolved = 0.2 x 92 = 18.4kJ.
The common cathodic protection metal used in steel pier for ships is
Magnesium is commonly used as a sacrificial anode for cathodic protection of steel structures like ship piers.
The activation energy of a chemical reaction can be reduced by
A catalyst provides an alternative reaction pathway with lower activation energy.
CaCO3(s) <=> CaO(s) + CO2(g). What is the expression for the equilibrium constant of the reaction above?
Since CaCO3 and CaO are solids (excluded from the equilibrium expression), Kc = [CO2].
The bleaching action of Sulphur (IV) oxide differs from that of chlorine in that
SO2 bleaches by reduction, while chlorine bleaches by oxidation - and SO2's bleaching effect is typically temporary/reversible, unlike chlorine's.
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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