Post Utme Chemistry Past Questions and Answers

Question 1086:

Blackboard chalk is a mixture of limestone and gypsum. A piece of blackboard chalk weighing \(5.42 g\) was immersed in \(HCl\). The \(CO _{2}\) produced weighed \(1.11 g\). What is the percentage of limestone in the calk?

A. \(67.0 \%\)
B. \(53.3 \%\)
C. \(50.8 \%\)
D. \(46.5 \%\)

Question 1087:

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 ____________

A. Fluorine
B. Chlorine
C. Bromine
D. Iodine

Question 1088:

Given the half-cell reaction, \(2 Br \rightarrow Br _{2}\), how many moles of electron will be required to produce \(0.56 dm ^{3}\) of bromine at s.t.p.?
[molar volume of gas at s.t.p. \(=22.4 dm ^{3}\) ].

A. \(0.05\)
B. \(0.10\)
C. \(0.20\)
D. \(1.00\)

Question 1089:

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?

A. \(C _{4} H _{9} OH\) and \(C _{4} H _{7} CHO\)
B. \(C _{4} H _{9} OH\) and \(C _{3} H _{7} CHO\)
C. \(C _{3} H _{7} OH\) and \(C _{3} H _{7} CHO\)
D. \(C _{4} H _{9} OH\) and \(C _{4} H _{9} CHO\)

Question 1090:

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 ____________

A. Distort the shape of molecules
B. Alter the angle between the atoms in molecules
C. Shorten the sigma bonds in molecules
D. Explain the shape of molecules