Chemical Tests
5 marks · EasyThis question is about testing for gases and for halide ions.
Describe the chemical test for ammonia gas and state the positive result.
A student wants to identify whether a colourless solution contains chloride ions.
i. State how the student would carry out a test for chloride ions.
ii. Name the precipitate formed and give its colour if chloride ions are present.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
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(a) Hold damp red litmus or universal indicator paper at the mouth of the test tube; ammonia turns the paper blue. · must show use of damp red litmus or universal indicator paper, test paper turns blue with ammonia gas
(b(i)) Add a few drops of dilute nitric acid to the solution, then add a few drops of silver nitrate solution. · must show add dilute nitric acid before silver nitrate, add silver nitrate solution
(b(ii)) A white precipitate of silver chloride forms. · must show name: silver chloride, colour: white
Show mark scheme and worked solution
Marking points
B1 (a) · 1 mark · Correct procedure: use of damp red litmus or universal indicator paper at mouth of test tube with ammonia.
B1 (a) · 1 mark · Correct result: paper turns blue in the presence of ammonia gas.
M1 (b(i)) · 1 mark · Add dilute nitric acid to the solution before testing.
M1 (b(i)) · 1 mark · Then add silver nitrate solution to the mixture.
A1 (b(ii)) · 1 mark · White precipitate of silver chloride forms (name and colour).
Worked solution
a) The chemical test for ammonia gas is carried out by holding a piece of damp red litmus paper or universal indicator paper at the mouth of the test-tube. If ammonia gas is present, it turns the paper blue.
b) (i) To test for chloride ions, add a few drops of dilute nitric acid to the solution to remove any interfering ions, then add a few drops of silver nitrate solution.
(ii) If chloride ions are present, a white precipitate of silver chloride forms.