The question was attempted by most candidates and the performance was good.
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)
100
=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
71
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)
(ii)
Natural Radioactivity |
Artificial Radioactivity |
New nuclei exist naturally |
Most of the nuclei do not exist |
|
naturally |
It is a spontaneous process |
Non-spontaneous/induced |
23592U +
10n →
23692U →
9236Kr +
14156Ba +
310n +Energy
(iv) Fission
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.
