Tests For Anions (aqeuous Solutions

Question 1

Test for chloride

Answer 1

• Prepare a solution of the unknown salt using distilled water and add a small amount of silver nitrate solution.
• If a white precipitate forms, the salt is either a chloride or a carbonate
• treat the precipitate with a small amount of concentrated nitric acid.
• If the precipitate remains unchanged, then the salt is a chloride.
• If carbon dioxide is formed and the precipitate disappears, the salt is a carbonate.

Question 2

Test for bromides and iodies

Answer 2

*like chlorides, bromides and iodide also form precipitates when they are reacted with silver nitrate

• silver chloride is a white precipitate
• silver bromide and silver iodide precipitates are pale yellow
• to determine whether the precipitate is a bromide or iodide, we use chlorine water and carbon tetrachloride
• chlorine water produces bromine gas from the bromide ions and colours the carbon tetrachloride reddish brown
• chlorine water produces iodine gas from iodide ions and colours the carbon tetrachloride purple

Question 3

Test for sulphate

Answer 3

• add a small amount of barium chloride solution to a solution of the test sal. If a white precipitate forms, the salt is either a sulphate or a carbonate
• if the precipitate is treated with nitric acid, it is possible to distinguish whether the salt is a sulphate or a carbonate (as in the test for chloride)

Question 4

Test for carbonate

Answer 4

• If a sample of the dry salt is treated with a small amount of acid, the production of carbon dioxide is a positive test for a carbonate
• if the gas is passed through limewater (an aqueous solution of calcium hydroxide) and the solution becomes milky, the gas is carbon dioxide
• it is the insoluble CaCO3 precipitate that makes the limewater go milky

Question 5

Redox reactions

Answer 5

• involve the transfer of electrons
• look at the charge of atoms
• if one has become more positive or negative then redox has occurred