Majority of the candidates could not correctly explain what a transition element was and state the reason why they exhibit variable oxidation state.
Many candidates could write the correct electron configuration for iron and why it’s paramagnetic. However, some candidates failed to realize that the 4s orbital is lower in energy than the 3d orbital, hence they wrote the electron configuration of iron as 1s22s22p63s23p63d64s2 instead of 1s22s22p63s23p64s23d6
Candidates exhibited adequate understanding of processes involved in the extraction of iron. Knowledge of elements which constitutes some specific alloys was satisfactorily displayed by majority of the candidates.
Part (d) was poorly attempted by the responding candidates.
The calculation from the equation involving mass and volume was correctly carried out by most candidates.
The expected answers are:
1(a) A transition element is one which has partially/incompletely filled d-orbital (in the neutral state/any of its positive oxidation states).
(b) (i) 1s22s22p63s23p64s23d6
(ii) I. Atom of iron has four unpaired electrons/parallel spin of electrons in the d-orbital
- Iron can lose electrons from 4s and 3d orbital for bond formation thereby giving it more than one oxidation state. Or Iron can lose electrons from 4s and 3d in redox reactions
- Carbon (IV) oxide, carbon (II) oxide, and slag/CaSiO3
Accept carbon dioxide, carbon monoxide
- C(s) + O2(g)
CO2(g)
CO2(g) + C(s) 2CO(g)
CaO + SiO2(s) CaSiO3(s)
Equations must be balanced
(c) (i) Iron and carbon
(ii) Copper and tin
(iii) Copper and zinc
- Lead and tin
(d) - mix the two aqueous solutions
- filter the resulting mixture
- silver chloride is obtained as residue
- wash the residue with water
- dry the residue
C(s) + O2(g) CO2(g)
12g of carbon gives 22.4 dm3 CO2
2.4g carbon gives 2.4
12 x 22.4
= 4.48 dm3
OR
C(s) + O2(g) CO2(g) states optional.
1 mole of C atoms = 1 mole CO2(g)
No of mole of C = 2.4 = 0.2 moles
12
1 mol of CO2 occupies 22.4 dm3
0.2 mol of CO2 = 0.2 x 22.4
1.0
= 4.48 dm3
