Observation

Majority of the candidates responded to this question and their performance was average.

In part (a), majority of the candidates stated the reason why a piece of red litmus paper turn blue when dipped into a solution.

 

In part (b), majority of the candidates named the main product formed when methanol reacts with methanoic acid;

 

In part (c), majority of the candidates could not write an equation for the preparation of ethyne from calcium carbide but were able to state one use of ethyne.

 

In part (d), majority of the candidates could not list the deductions that can be made from the qualitative and quantitative analysis of an organic compound.

 

In part (e), majority of the candidates stated the differences between burning and rusting.

 

In part (f), majority of the candidates could not describe what would be observed when concentrated hydrochloric acid reacts with K2Cr2O7(aq).

 

In par (g), majority of the candidates were able to name the products formed when a compound of formula CnH2n+2 is completely oxidized with oxygen.

 

In part (h), majority of the candidates stated the laws of chemical combination.

 

In part (i), majority of the candidates defined neutralization reaction.

 

In part (j), majority of the candidates stated one way of increasing the rate of dissolution of a solid in a liquid.

 

The expected answers include:

1.       Because ammonia solution is basic/alkaline
2. (i)  Methylmethanoate 

(ii)       

– heat/warm  
– add few drops of Conc. H2SO4 /HCl         
                                                                                                                             

3. (i) CaC2(s) + 2H2O(l) → C2H2(g) + Ca(OH)2(s)

(ii)

• production of oxyacetylene flame
• polymer production
• artificial ripening of fruits
• fuel for miners Lamp
• production of other compounds e. g. ethanal
• as an illuminant    

 

4.   
   • types of bonds
   • types of elements
   • functional groups
   • number of atoms of different elements
   • percentage composition of the elements in the compound
   • spatial arrangements of atom in a molecule.
5.                                                          

Burning	Rusting
- large amount of heat is released in burning - burning is a rapid process - burning occurs at high temperature - is associated with diverse materials - requires oxygen only	-  low amount of heat is release in rusting -  rusting is a slow process -  occurs at low temperatures -  is associated with iron and iron-containing materials - requires oxygen and water/moisture

 

6. (i)it turns orange K2Cr2O7 green liberating yellowish green gas

(ii)   -     effervescence/production of a colourless gas

formation of green solution

                                                                                                           

7. (i)    -    carbon (IV) oxide

        -    water

(ii)        CnH2n+2 +  O2 → nCO2 + (n+1) H2O

 

• All pure chemical compounds contain the same elements combined in the same proportion by mass
• During the cause of a chemical reaction matter is neither created nor destroyed.
• When two elements A and B combine to form more than one different compounds, the different masses of A that combine separately with a fixed mass of B are in a simple ratio.
9. Heat produced when an acid reacts with a base to form salt and water.

Accept
Heat change when one mole of H+ from an acid reacts with one mole of OH- from an alkali to form one mole of water

 

10. -          
• Heating the mixture / increase the temperature
•      Stirring the mixture
•      Grinding the solid into powder/increasing surface area of the solid