Observation

This was a compulsory question. Majority of the candidates that responded to it performed fairly.

In part (a), majority of the candidates could not give a complete definition of the term compound.

In part (b), majority of the candidates stated temperature and pressure instead of high temperature and high pressure as conditions necessary for the cracking of petroleum fractions.

In part (c), majority of the candidates mistook compounds of transition elements used as catalyst for the transition elements that are used as catalysts.

In part (d), majority of the candidates could not write an equation for the reaction between zinc dust and silver trioxonitrate (V) solution..

In part (e), majority of the candidates could calculate the relative atomic mass of oxygen from the given isotopes and relative abundance.

In part (f), majority of the candidates listed two ores of iron correctly.

In part (g), majority of the candidates were not familiar with the term biotechnology.

In part (h), majority of the candidates listed forces that can exist between covalent molecules.

In part (i), majority of the candidates could not give the complete definition of the term element.
In part (j), majority of the candidates could not state two sources of methane in the atmosphere.

In part (f), majority of the candidates could not explain why the trend of the boiling points for group VII element is in the order I2 > Br2 > Cl2.

The expected answers include:

(a)  A compound is defined as a substance containing two or more elements / different atoms chemically combined (in a fixed proportion by mass)                         
(b) -  high temperature
-  catalyst
-  high pressure

                                                                                               
(c)-   Iron
-    Nickel
-    Palladium
-    Platinium
-    Rhodium

(d)(i)  Zn(s) + 2AgNO3(aq) → Zn(NO3)2(aq) + 2 Ag(s)                                      

(ii) I.  AgNO3 / Ag+is reduced                                 
II.   Zn is oxidized        

(f)        -           haematite (Fe2O3)/ Iron (III) oxide
            -           magnetite (Fe3O4)/Iron (II) Iron (III) oxide
            -           limonite Fe2O3.nH2O/Iron (III) oxide hydrate(accept FeO(OH).nH2O)
            -           iron pyrites FeS/Iron (II) Sulphide
            -           Siderite/spathic iron ore /FeCO3/Iron (II) trioxocarbonate (IV)
                                                                                               

(g)        (i)         It is the use of biological processes / organisms / system  to manufacture
useful products

(ii)        -           garri, fufu, kenkey, bread
-           bio-gas,
-           alcoholic beverages (beer, whisky, burukutu, gin, etc)
-           drugs (vaccines, hormonal, antibiotics)
-           enzymes
-           biodegradable plastics
-           pests control
-           organic fertilizers

(h)        An element is defined as a substance containing only one type of atom / substance which
cannot be broken down into a simpler one. 

(i)         -           land fill sites / compost
-           marshes/swampy area
-           rice (paddy) fields
-           bacteria
-           natural gas
-           biomass burning
-           crude oil/petroleum
-           decay of organic matter
-           raising of livestock
-           coal mine

(j)         The molecules are held together by van der Waal’s forces . The larger the atom, the greater the van der Waal’s forces/increase in molecular mass and hence the higher the boiling point.