OAU Chemistry 2017/2018 Past Questions

Blackboard chalk is a mixture of limestone and gypsum. A piece of blackboard chalk weighing 5.42g was immersed in HCl. The CO₂ produced weighed 1.11g. What is the percentage of limestone in the calk?

In the Lassaine's test for the halogens, the sodium fusion extract is acidified and then treated with silver nitrate. A pale yellow precipitate soluble in ammonium hydroxide shows the presence of,

Given the half-cell reaction, 2Br → Br₂, how many moles of electron will be required to produce 0.56dm³ of bromine at s.t.p.? [molar volume of gas at s.t.p. = 22.4dm³].

One mole of an alkanol and one mole of an alkanal, each containing n moles of carbon atoms in its molecule, was separately combusted in excess oxygen. The volumes of steam produced by the compounds were in ratio 5:4. What are the respective formulae of the compounds?

The basic tenet of valence bond electron pair repulsion theory is that the pairs of electrons making the sigma bonds dictate the shape of molecules. The pi-bonds often encounter in some molecules serve to,

The equilibrium constant at constant pressure, Kp for the reaction,
2NO(g) + Cl₂(g) → 2NOCl(g) is 800. The partial pressures of the gas mixture at equilibrium are 0.02 atm each for NO and Cl₂. What is the partial pressure of NOCl in the mixture?

How many sigma (σ) bonds are there in the molecule below:

The enthalpy changes for the atomization of methane and ethane are 1648 and 2820kJmo1^-1 respectively. The C-C mean bond dissociation energy in kJmol^-1 is therefore,

What volume of 0.750moldm^-3 Na₂CO₃ solution could be diluted to 250cm³ to reduce the concentration to 0.025moldm^-3?

An organic compound with the molecular of C₄H₈O has the isomers
(i) butanal (ii) cyclobutanol (iii) cyclobutanone (iv) 2 - methylpropanal

0.125 mol of magnesium is dropped into 25cm³ of 4.0moldm^-3 HCl, how many moles of hydrogen gas are evolved? [Mg = 24]

Which of the followings is thermally stable?

An atom has a core and outside the core an electron occupies an orbital for which the principal quantum number, n = 4,l= 0, m = 0 and s = +1/2 or -1/2. The atom is likely to be

An element B, has two isotopes$↖{20}↙{10}B$ and $↖{22}↙{10}B$ present in ratio 2:3. The relative atomic mass of B is,

A chloroform solution of pure organic compound was spotted at a distance 0.80cm from the base of a 20cm long chromatoplate. If the compound has the Rf value of 0.50 and moves half way up the 20cm long plate, what is the distance of the solvent front from the top of the plate upon elution?

The equilibrium constant, Kc for the reaction, NO(g) + 1/2 O₂(g) → NO₂(g), is 35.2. What is the value of Kc for the reaction, NO₂(g) → NO(g) + 1/2 O₂(g)?

CH₃CH₂CI + NaOH → CH₃CH₂OH + NaCI
The above reaction is best described will proceed to form the products by a process known as

What quantity of current is required to deposit 2.4g of copper in a period of 750 seconds during an electrolytic deposition process? [Cu = 64, 1F = 96500 coulomb]

The standard reduction potentials for the following half-cell reactions are,
2H₂O_(l) = O_2(g) + 4H⁺ (aq) + 4e E⁰ = -1.23V
2H₂O₂(l) = 2O_2(g) + 4H⁺(aq) + 4e E⁰= -0.68V
What is the Ea for the reaction, 2H₂O_2(l) = 2H₂O_(l) + O_2(g) at 298K?