Flashcards
Tests for Ions
Cards in this deck (16)
- 1What is a false positive?A result that suggests that a particular ion is present when it actually isn't. This can happen if there are ions present that will interfere with the test you are carrying out
- 2How can you prevent false positives?You can sometimes add a substance to your sample to remove problematic ions
You should also do the three tests in the following order:
Carbonates --> Sulphates --> Halides - 3What is the test for carbonates?Add a dilute strong acid (e.g. dilute nitric acid or dilute hydrochloric acid). If carbonates are present, then carbon dioxide will be released
- 4Give the half equation for the test for carbonatesCO₃²⁻ + 2H⁺ --> CO₂ + H₂O
- 5What is the test for carbon dioxide?Bubble the gas through limewater - if there is CO₂ present, it'll turn the limewater cloudy
- 6TRUE OR FALSE All sulphates are soluble in waterFALSE
Most sulphates are soluble in water, however there are some which are insoluble. E.g. barium sulphate is insoluble - 7Describe the method for the sulphate testTo test for a sulphate ion, add a few drops of barium nitrate solution (Ba(NO₃)₂)
- 8If the sulphate test is positive, a white precipitate will be formed. What is this precipitate?Barium sulphate
- 9Give the half equation for the formation of barium sulphate in the sulphate testSO₄²⁻ + Ba²⁺ --> BaSO₄
- 10Complete the sentences: In the test for sulphates, a false positive may occur due to ____________ or ____________ ions. In the test for carbonates, you add a ________ strong acid which will react with any carbonates or sulphites present so that they won't interfere with the test.In the test for sulphates, a false positive may occur due to CARBONATE or SULPHITE ions. In the test for carbonates, you add a DILUTE strong acid which will react with any carbonates or sulphites present so that they won't interfere with the test.
- 11What is the test for halides?Add nitric acid and silver nitrate solution
To distinguish between different colours, the solubility is tested using ammonia (dilute and concentrated) - 12If the test for halides is positive, a precipitate is formed. The colour of the precipitate determines the halide present. What are the colours of silver chloride, silver bromide or silver iodide?SILVER CHLORIDE = white
SILVER BROMIDE = cream
SILVER IODIDE = yellow - 13TRUE OR FALSE: Ammonia gas is acidicFALSE
Ammonia gas is alkaline - 14What is the test for ammonia?Check it using a damp piece of red litmus paper. If ammonia is present, the paper will turn blue.
Ammonia also has a distinctive, pungent smell - 15Outline the method used to test whether a substance contains ammonium ions (NH₄⁺)1. Add a few drops of aqueous sodium hydroxide and warm the mixture
2. Hold a piece of damp litmus paper near the top of the test-tube
3. If the paper turns blue, ammonia is being given off and there are ammonium ions in the substance - 16Give the half equation for the reaction between ammonium ions and hydroxide ionsNH₄⁺ + OH⁻ --> NH₃ + H₂O
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- User has deleted their subject information Flashcards on Tests for Ions, created by Deleted user on 05/03/2018.
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- Deleted user · Mar 2018
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- Mar 5, 2018
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- Created by Yinka F · Mar 4, 2018
- Copied by Yinka F · Mar 5, 2018
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