All 11 questions from the Post-UTME Screening (Post-UTME) Chemistry 2012 Objective paper, with the correct answer and a full explanation for each. Free, no signup needed.
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A brand of ink containing cobalt(II) and copper(II) ions can be separated into its various components by
Chromatography separates different coloured/dissolved components of a mixture like ink based on differing mobility.
Which of the following substances is a mixture?
Sea water is a mixture of water, dissolved salts and other substances, unlike the pure/single compounds listed.
If the quantity of oxygen occupying a 2.71dm3 container at a pressure of 0.825 atmospheres and 300K is reduced by one half, what is the pressure exerted by the remaining gas?
Halving the amount of gas at constant volume and temperature halves the pressure: 0.825/2 = 0.413atm.
Which of the following substances has the lowest vapour density? (O=16, Cl=35.5, H=1, C=12)
Vapour density = molar mass/2. Ethanol (molar mass 46) has the lowest molar mass among those listed, giving the lowest vapour density.
The atomic numbers of two elements X and Y are 12 and 9 respectively. The bond in the compound formed between the atoms of these two elements is
X (Z=12, Mg, a metal) and Y (Z=9, F, a non-metal) form an ionic bond through electron transfer.
The greater the difference in electronegativity between bonded atoms, the
A larger electronegativity difference between bonded atoms results in a more polar (ionic-character) bond.
In the purification of town water supply, alum is used principally to
Alum acts as a coagulant/flocculant, clumping together suspended fine particles so they can settle or be filtered out.
Oil spillage in ponds and creeks can be cleaned up by
Spraying with detergent/dispersant breaks up the oil slick, aiding its dispersal and biodegradation.
The solubility of Na3AsO4(H2O)12 is 38.9g per 100g H2O. What is the mass percentage of Na3AsO4 in the saturated solution? (As=75, Na=23, O=16, H=1)
Flagged: this multi-step hydrate mass-percentage calculation gave results that did not cleanly match the listed options when computed independently; the closest option is given with reduced confidence.
The basicity of tetraoxophosphate (VI) acid is
Tetraoxophosphate(VI) acid, H3PO4, has 3 replaceable (acidic) hydrogen atoms, giving a basicity of 3.
The scum formed when soap is mixed with hard water could be
This item's precise intended answer (soap scum is chemically calcium/magnesium salts of fatty acids) was not exactly matched by any listed option; option D is presented as the closest match given the hard-water magnesium ion context, flagged for uncertainty.
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