(a) Define each of the following terms:
[ Avogadro’s constant = 6.02 x 1023 particles mol”] [12 marks]
(c) (i) Define the term natural radioactivity.
23592U + 10n →x92U →9236Kr + 14156Ba + y10n +Energy
In part (a)(i) and (ii), candidates correctly defined atomic number and isotopy thus:
– atomic number is the number of protons (in the nucleus) of an atom of an element/the number of electrons in a neutral atom.
– isotopy is a phenomenon whereby atoms of an element exhibit different mass numbers but have the same atomic number/the same number of protons but different number of neutrons.
In part bli], candidates correctly stated the sub atomic particles and the corresponding number present in the two isotopes as follows:
Proton Electron Neutron
3517R 17 17 18
3517R 17 17 20
In (b)(iiL I and II, candidates correctly calculated the relative atomic mass of the element but most of them could not infer that the element is diatomic and hence lost mark in II. The expected calculations from candidates were as follows:
(I) ReI. atomic mass of R = (75.5 x 35 + (24.5 x 37)
=35.49 or = 35.5
(II) Molar mass of R2 = 2 x 35.5
= 71 gmol-1
71g → 602 x 1023
No. of molecules of R2
= 6.02 X 1023 x 17.75
1.51 X 1023 molecules
In part (c)(i),(ii), (Hi) and (Iv), candidates correctly defined natural radioactivity, stated the differences between natural and artificial radioactivity, copied, and completed the given nuclear reaction and stated the type of reaction exhibited by the reaction thus:
(i) It is spontaneous disintegration/decay of a nucleus to produce radiations/particles (and energy)
New nuclei exist naturally
Most of the nuclei do not exist
It is a spontaneous process
23592U + 10n →23692U →9236Kr + 14156Ba + 310n +Energy
In part(d), only few candidates knew that ethanol is completely miscible with water because the two compounds contain hydroxyl group (OH)/both are polar which allows for (intermolecular) hydrogen bonding.