IGCSE Chemistry: Specimen Questions with Answers 238 - 239 of 240

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Question 238

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Describe a test for iodide ions

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You can test to see if a solution contains iodide ions by using silver nitrate. If silver nitrate solution is added to a sample of water containing iodine ions the silver halide is precipitated. This is because the silver halides are all insoluble in water.

Iodide Ions

Question 239



Water has been contaminated with sea-water.

Which substances can be removed by chlorination and filtration?


Choice (4)


Bacteria, sand and sodium chloride


Bacteria and sand only


Bacteria and sodium chloride only


Sand and sodium chloride only




Correct option is A i.e.. bacteria, sand and sodium chloride because Water chlorination is the process of adding chlorine or hypochlorite to water. This method is used to kill certain bacteria and other microbes in tap water as chlorine is highly toxic. In particular, chlorination is used to prevent the spread of waterborne diseases such as cholera, dysentery, and typhoid. Filtration is any of various mechanical, physical or biological operations that separate solids from fluids (liquids or gases) by adding a medium through which only the fluid can pass. The fluid that passes through is called the filtrate.

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