Heep Woh College

Form 5 Chemistry Quiz 11

Chapter 28 : Detergents

Marking Scheme

 

1.    (a)        Refer to NOTE: C28/P6

Detergent has a long hydrocarbon tail / non-polar tail and

an ionic head / polar head.                                                                                1

        The hydrocarbon tail is hydrophobic / dissolves in oily dirt and the polar

                head is hydrophilic / dissolves in water. + Diagram                                            1

        Upon agitation, the oily dirt splits up into small droplets.

        Repulsion of the charged droplets helps to disperse the dirt.

+ Diagram                                                                                                                     1

 

        (b)        Solution contains Mg²⁺ / Ca²⁺                                                                                    1

 

        (c)  (i)        Detergent produced by animal fat or plant oil.                                         1

               or       (Sodium) salt of long chain alkanoic acid.                                                   (1)

               (ii)        Fat / oil + strong alkali / NaOH / KOH and heat                                            1,1

               (iii)        Soapless detergent because it does not form scum.                         1

 

        (d)  (i)        Can be decomposed / broken down by micro-organisms.                      1

                       NOT accept “degrade”.

               (ii)        Form thick foam on water and kills aquatic animals.                              1

               (iii)        Bacteria use up (dissolved oxygen) in water when they break down

                       detergents and aquatic animals die of lacking oxygen.                      1

 

2.    (a)  B:        HCOO^-K⁺                                                                                                                 1

               C:        HCOOH                                                                                                                   1

               D:        CH₃CH₂CH₂OH                                                                                                     1

 

        (b)        Reaction I:  Alkaline hydrolysis / saponification           (correct spelling)        1

                Reaction II: Acidic hydrolysis                                            (correct spelling)        1

 

 

The End