All 22 questions from the Post-UTME Screening (Post-UTME) Chemistry 2013 Objective paper, with the correct answer and a full explanation for each. Free, no signup needed.
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The cell membranes consist of
Cell membranes are composed mainly of a phospholipid bilayer with embedded proteins (the fluid mosaic model).
The maintenance of a constant internal environment of an organism is known as
Homeostasis is the maintenance of a stable internal environment despite external changes.
The most sensitive part of the retina is called
The fovea centralis has the highest concentration of cone cells and is the point of sharpest vision.
Which of the following substances is not a homogenous mixture?
Flood water typically contains visible suspended particles/debris, making it a heterogeneous mixture, unlike the others listed.
There is a large temperature interval between the melting point and boiling point of a metal because
Melting only loosens the rigid lattice structure while the metallic bonding (delocalised electron sea) persists; boiling requires complete separation of atoms, breaking metallic bonds - requiring far more energy and a higher temperature.
How many moles of H+ are there in 1dm^3 of 0.5M solution of H2SO4?
H2SO4 is diprotic (2 H+ per molecule). Moles H+ = 2 x 0.5M x 1dm3 = 1.0 mole.
A given mass of gas occupies 2dm3 at 300K. At what temperature will its volume be doubled, keeping the pressure constant?
By Charles' law, V/T is constant: 2/300 = 4/T2 => T2 = 600K.
If 100cm3 of oxygen passes through a porous plug in 50 seconds, the time taken for the same volume of hydrogen to pass through the same porous plug is
By Graham's law, rate is inversely proportional to sqrt(molar mass). t(H2) = t(O2) x sqrt(M(H2)/M(O2)) = 50 x sqrt(2/32) = 50/4 = 12.5s.
Which of the following is a measure of the average kinetic energy of the molecules of a substance?
Temperature is directly related to the average kinetic energy of a substance's molecules.
Four elements P, Q, R and S have 1, 2, 3, and 7 electrons in their outermost shells respectively. The element which is likely to be a metal is
Elements with few outer-shell electrons (here, P with just 1) tend to lose them easily, a key metallic property.
Which of the following gases dissolves in water vapour to produce acid rain during rainfall?
Sulphur (IV) oxide (SO2) dissolves in atmospheric water to form sulphurous/sulphuric acid, a major cause of acid rain.
Water for town supply is chlorinated to make it free from
Chlorination is primarily used to disinfect water, killing harmful bacteria.
Which of the following physical processes cannot be explained by the molecular theory of matter?
Radiation of heat is energy transfer via electromagnetic waves, which does not require molecules/a medium, unlike the other processes listed.
A spring balance which is suspended from the roof of a lift carries a mass of 1kg at its free end. If the lift accelerates upward at 2.5ms^-1^2, determine the reading on the spring balance (g=10ms^-2)
Reading = m(g+a) = 1 x (10+2.5) = 12.5N.
An object of weight 10N immersed in a liquid displaces a quantity of the liquid. If the liquid displaced weighs 6N, determine the upthrust on the object.
By Archimedes' principle, upthrust equals the weight of fluid displaced = 6N.
Which of the following statements about pressure is NOT correct? Pressure
Pressure = Force/Area, so pressure decreases (not increases) as surface area increases; this statement is the incorrect one.
A block weighing 15N rests on a flat surface and a horizontal force of 3N is exerted on it. Determine the frictional force on the block.
If the block remains stationary, static friction balances the applied force exactly: friction = 3.0N.
The time rate of change of momentum is
Newton's second law: force = rate of change of momentum.
Electrical resistance is a property of an electrical conductor that causes electrical energy to be converted into
Resistance causes electrical energy to be dissipated as heat energy (Joule heating).
A simple machine with an efficiency of 75% lifts a load of 5000N when a force of 500N is applied to it. Calculate the velocity ratio of the machine.
Efficiency = Mechanical Advantage/Velocity Ratio. MA = Load/Effort = 5000/500 = 10. VR = MA/efficiency = 10/0.75 = 13.3.
The amount of heat given out or absorbed when a substance changes its state at a constant temperature is known as
This describes latent heat - the heat absorbed/released during a phase change without a temperature change.
Which of the following physical quantities affect the saturated vapour pressure of a liquid?
Saturated vapour pressure of a liquid depends on temperature.
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