Wednesday 13 November 2013

Rusting of Iron Quiz (answered)

 

Name/# /ClASS      : MARKS:

DAY, DATE :

Answer the following questions briefly on your “kertas ulangan”, then fasten the question sheet and the answer sheet securely together. You are not allowed to use any correction tools. There are 40 marks possibly. 


  1. Define the meaning of :

    1.  “corrosion”  and  “rusting”, what are the differences the both terms.   [4 marks]

    2. Why  the rusting of iron is called a slow reaction [3 mark]








  1. Write chemical equiation for:

  1. the oxidation of iron atoms to iron(II) ions. [2 marks]

Fe(s) ­čí¬ Fe2+(aq)    +    2e-

  1. the reduction of oxygen in the presence of water to form hydroxide ions. [2 marks]

O2(g)   +   2H2O(l)   +   4e-      ­čí¬     4OH-(aq)


  1. Suggest why no corrosion has occurred in tube 2. [3 marks]

keyword: free moisture/dry air

  1. Suggest why no corrosion has occurred in tube 3. [3 marks]

Keyword: boiled water—free O2; preventing by oil layer


  1. Suggest why there is more corrosion in tube 4 than in tube 1. [3 marks] keyword: compare the oxygen content of the both tube.


  1. Suggest why corrosion of an iron object is reduced (or stopped) in each of the following situations.

  1. Outer space [2 marks] keyword: no oxygen

  2. At the bottom of the ocean. [2 marks] keyword: limited/lack of oxygen

  3. When the object is coated with oil. [2 marks] keyword: oil prevent O2 and H2O away from the metals


  1. Metal rubbish bins are often coated with zinc. Metal food containers are coated with tin.

  1. Why the zinc coating on rubbish bins protects the iron from corrosion. [3 marks] keyword: reactivity

  2. Why is a zinc coating not suitable for use on food containers? [3 marks] keyword: rust; healthy


  1. Complete this table showing whether there is rusting or not, and if it occurs, whether the corrosion is slow, fast or very fast. [4 marks]


Speed of corrosion

Water

Air

Salt

a.

x

x

b.

x

x

c.

x

d.

Keyword: rust : the present of O2 and water

  1. Why does iron corrode faster/very fast in previous questions (no. 8) [2 marks] keyword: catalyst


Why are pieces of household equipment packed in cartons with a sachet of silica gel? [2 marks] keyword: drying agent; good maintenan

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