All 16 questions from the Post-UTME Screening (Post-UTME) Chemistry 2008 Objective paper, with the correct answer and a full explanation for each. Free, no signup needed.
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The difference in mass number (A) of isotopes of the same element is due to a difference in
Isotopes have the same proton number but differ in neutron number.
Which of the following pairs of particles each have the same number of electrons? [Ar=18]
Na+ has 10 electrons; F- has 10 electrons - matching.
A mixture of 0.20 mole of Ar, 0.20 mole of Ne and 0.30 mole of He exerts a total pressure of 2.1 atmosphere. What is the partial pressure of He in the mixture?
Mole fraction He = 0.30/0.70 = 0.4286. Partial pressure = 0.4286 x 2.1 = 0.90 atmosphere.
The pOH of a solution is 12.23; calculate the hydrogen ion concentration of the solution.
pH = 14-12.23 = 1.77. [H+] = 10^-1.77 = 1.7x10^-2 mol/dm^3.
Which of the following is an 'artificial' element?
Plutonium is primarily produced synthetically, the classic man-made element among these options.
One common fraction may be represented ionically by the equation Ba2+ + SO4 2- -> BaSO4. This occurs during
This precipitation reaction is a double decomposition (double displacement) reaction.
White phosphorus is stored under water because it
White phosphorus spontaneously ignites in air due to its very low ignition temperature; storing under water excludes air.
When aluminium tetraoxosulphate (VI) reacts with excess sodium hydroxide, the formula of one of the compounds formed is
With excess NaOH, amphoteric aluminium hydroxide dissolves to form soluble sodium aluminate, NaAl(OH)4.
An alloy of copper and tin used in electrical contracts is
Bronze is an alloy of copper and tin.
Kerosene and petrol (gasoline) are
Kerosene consists of longer-chain (bigger) hydrocarbon molecules than petrol.
The preparation of ethoxyethane (C2H5OC2H5) from ethanol can be considered as
Ether formation from an alcohol is an intermolecular dehydration reaction.
Which of the following gives the correct formula of the fatty acid present in palm oil?
Palmitic acid, the major fatty acid in palm oil, is CH3(CH2)14COOH.
Glycerol had the typical properties of
Glycerol is a trihydric alcohol.
A certain natural product contains the ester glycerol palmitate. Soap can be made from this by
Boiling a fat/oil with NaOH is saponification, producing soap and glycerol.
Which of the following is NOT a thermosetting plastic?
Terylene is a thermoplastic (polyester), unlike the other thermosetting resins listed.
Which of the following statements is/are correct? (i) One mole of sodium atoms contains 6.02x10^23 atoms and weighs 23g (ii) One mole of magnesium atoms contains 6.02x10^23 atoms and weighs 24g (iii) One mole of oxygen atoms contains 6.02x10^23 atoms and weighs 16g
All three statements correctly describe one mole of the respective atoms.
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