Question 1A

 

 

(a)        Define the term hydrocarbon.                                                                        [2 marks]

(b)        State the conditions necessary for cracking long-chain hydrocarbons
to produce more gasoline.                                                                   [2 marks]
(c)        Define oxidation in terms of electron transfer.                                   [2 marks]
(d)       State two reasons for electroplating metallic objects.             [2 marks]
(e)        Give the names of the following compounds:
(i)         CH3CH=CHCH2CH3;
(ii)        CH3CH2CH2-C-OH.                                                               [2 marks]
O                                                                      
(f)        State Dalton’s law of partial pressures.                                              [2 marks]
(g)        (i)         Give two reasons for preferring alloys to their pure metals.   [2 marks]
(ii)        List the constituent elements in steel.                                     [5 marks]
(h)        State the type of bonding in the following substances:         
(i)         aluminum chloride;
(ii)        sodium metal;
(iii)       sodium chloride.                                                                     [3 marks]

1. (i)         What are isomers?

1. State why helium atom does not react with other elements

to form compounds.                                                                            [3 marks]
(j)         What are galvanic cells?                                                                     [2 marks]
This was a compulsory question.  Majority of the candidates that answered this
question performed fairly.

In part (a), majority of the candidates could not define hydrocarbons correctly.  Others
defined it as the combination of hydrogen and carbon.

In part (b), majority of the candidates were able to state two conditions necessary for cracking long-chain hydrocarbons to produce more gasoline.

 In part (c), majority of the candidates defined oxidation as a process of electron loss, while quite a number of them could not define it correctly. They wrote other definitions of oxidation.

 In part (d), majority of the candidates could only give one correct reason for electroplating metals instead of two.  However, a few gave two correct reasons.

In part (e), majority of the candidates could not name the organic compounds. Only few of the candidates named the two compounds correctly.

In part (f), majority of the candidates stated Dalton’s Law of partial pressure correctly.  Few did not show in their statements that the law holds for gases which do not react chemically, consequently, they lost the marks allocated to the question.

In part (g) (i), few of the candidates gave two correct reasons for preferring alloys to their pure metals. However, majority of the candidates gave only one reason.
In part (g) (ii), majority of the candidates could not list the constituent elements in steel.

In part (h) (i), majority of the candidates could not state the bond type in aluminum chloride.

In part (h) (ii), few of the candidates could not state the bond type in sodium metal.

In part (h) (iii), majority of the candidates could state the type of bonding in sodium chloride, while a few could not.

In part (I) (i), majority of the candidates defined isomers correctly.  Some of the candidates defined it as “elements with the same molecular formula but different structures”.

In part (I) (ii), majority of the candidates stated correctly, why helium atom does not react with other elements to form compounds, while some wrote that it is an inert gas. None inclusion of stable duplet structure made them to lose the marks allocated to the question.

In part (j), majority of the candidates were not familiar with electrochemical cells hence, could not explain galvanic cells.