All 11 questions from the Post-UTME Screening (Post-UTME) Chemistry 2011 Objective paper, with the correct answer and a full explanation for each. Free, no signup needed.
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Which of the following pairs illustrate isotopy?
Isotopes are atoms of the same element with different numbers of neutrons; hydrogen and deuterium are isotopes of hydrogen.
A gas occupying an initial volume of 2dm^3 is heated and allowed to expand to 6dm^3 at constant pressure. The ratio of the initial absolute temperature to the final absolute temperature is
At constant pressure, V is proportional to T, so T1:T2 = V1:V2 = 2:6 = 1:3.
Which of the following reactions is accompanied by the second ionization energy of an element?
The second ionization energy corresponds to removing an electron from an already singly-charged cation (X+ to X2+).
How much heat will be liberated if 10g of hydrogen burns in excess oxygen according to the thermochemical equation H2(g)+1/2O2(g) -> H2O(l), delta-H=-286KJ
Moles H2 = 10/2 = 5mol. Heat released = 5 x 286 = 1430KJ (i.e. -1430KJ).
Which of the changes determines the spontaneity of a chemical reaction?
The Gibbs free energy change (delta-G) determines whether a reaction is spontaneous.
Which of the following statements is NOT correct of group (VII) elements? They
Group VII (halogens) actually have relatively HIGH ionization potentials, not low, making this the incorrect statement.
Calculate the minimum volume of oxygen required for the complete combustion of a mixture of 20cm^3 of CO and 20cm^3 of H2
2CO+O2->2CO2 needs 10cm3 O2 for 20cm3 CO. 2H2+O2->2H2O needs 10cm3 O2 for 20cm3 H2. Total O2 = 10+10=20cm^3.
Calculate the quantity of electricity required to deposit 64.0g of copper from copper (II) chloride solution [Cu=64, 1F=96500C]
Moles Cu = 64/64=1mol. Cu2+ +2e- -> Cu needs 2 moles electrons = 2F = 2x96500=193000C = 1.93x10^5C.
Which of the reactions of marble with dilute HCl is fastest?
Both higher temperature and smaller particle size (powder, greater surface area) increase reaction rate; powder at the higher temperature (50 degrees C) reacts fastest.
The number of neutrons contained in the nucleus of U-92-238 is
Neutrons = mass number - atomic number = 238 - 92 = 146.
A sample of orange juice is found to have a pH of 3.80. Which is the concentration of hydroxide ion in the juice?
pOH = 14-3.80 = 10.20. [OH-] = 10^-10.20 = 6.3 x 10^-11 mol/dm^3.
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