Questions on REDOX ocr

Past paper questions and answers related to REDOX

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June 2009

Q)All of the methods shown in Table 1.1  involve the conversion of chloride ions to chlorine    molecules. Write a half-equation for this reaction.  

 a) 2Cl- --> Cl2 + 2e-    

Q) Chlorine can be used to produce bromine. The chlorine is passed through a solution, obtained from seawater, which contains Bromide ions. Cl2 + 2Br- ==> Br2 + 2Cl- Give the oxidation states of Cl2 and Cl-. Cl2: 0   Cl-:-1 Q) Give the name of the process in which Cl2 is converted in to Cl- giving an explanation of your choice.

a)Reduction, as Chlorine has gained electrons and the oxidation state has decreased.

Q)Explain why the reaction represented happens, by reference to the oxidising ability of Chlorine and Bromine. a) Chlorine displaces Bromine because it is more oxidising than Bromine.     

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June 2010

Q) Iodine can be extracted from some types of seaweed which have taken up iodide compounds from the sea water. Iodide is present in seawater as both iodide I- and iodate ions IO3-.

Give the oxidation state of iodine in I- and IO3-

a) I-: -1   IO3-: +7

Q) IO3- + 3SO2- ==> 6H+ + 3SO4 (2-) + I-

Which element has been oxidised in the reaction?

a) Sulfur

Q) This equation is the incomplete half equation for the conversion of iodate ions to iodide ions.

a) IO3- + 6H+ +6e-  ==> I- + 3H20

Q) Chlorine atoms are more readily reduced than iodide atoms. 

State what is mean't by reduction in terms of electrons.

a) Reduction is the gain of electrons.

Q) Suggest why Chlorine atoms are more readily reduced than iodide atoms.

Chlorine is a smaller atom with less sheilding than Iodine, and therefore it's nucleus can attract the electron it needs to be reduced more strongly than Iodine.

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June 2011

Q) Write the half equation for the conversion of iodide ions to iodide in this equation:

I2 + 2S2O3 (2-) ==>S4O6 (2-) +2I-

a) I2 +2e- ==> 2I-

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