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CAIE A-Level Chemistry 11.4.2 Chlorine Water Purification Question Bank

Practise explaining how chlorine purifies water by forming HOCl or ClO-, then linking the active species to killing bacteria.

Syllabus
2028–2030
Course
Chemistry 9701
Level
AS

Exam points

  • write the equation for Cl2 reacting with water to form HCl and HOCl
  • identify HOCl or ClO- as the active species responsible for killing bacteria
  • state water purification or bleach use from chlorate(I) species when context is given

11.4.2—Explain question 1

[Maximum number: 2]

The halogens chlorine, bromine and iodine show trends in chemical and physical properties down the group.

Table 3.1 shows some properties of chlorine, bromine and iodine.

Table 3.1

Table 3.1

Explain, with the use of an equation, how chlorine, Cl2\mathrm{Cl}_{2}, is used in water purification. State the role of the active species produced.

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