CHAPTER 5. THE CHEMICAL INDUSTRY 5.3
+ –
anode cathode
NaCl
Cl 2 H 2
NaCl
NaOH
H 2 O
membrane
(a) What ions are present in the electrolyte in theleft hand compartment of the
cell?
(b) Give the equation for the reaction that takesplace at the anode.
(c) Give the equation for the reaction that takesplace at the cathode.
(d) What ion passes through the membrane while these reactions aretaking
place?
Chlorine is used to purify drinking water and swimming pool water. The
substance responsible for this process is the weak acid, hypochlorous acid
(HOCl).
(e) One way of puttingHOCl into a pool is tobubble chlorine gas through
the water. Give an equation showing how bubbling Cl 2 (g) through water
produces HOCl.
(f) A common way of treating pool water is by adding ’granular chlorine’.Gran-
ular chlorine consists of the salt calcium hypochlorite, Ca(OCl) 2. Give an
equation showing howthis salt dissolves in water. Indicate the phaseof
each substance in the equation.
(g) The OCl−ion undergoes hydrolysis , as shown by the following equation:
OCl−+ H 2 O� HOCl + OH−
Will the addition of granular chlorine to pure water make the water acidic,
basic or will it remain neutral? Briefly explain your answer.
(IEB Paper 2, 2003)
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