Required Practical 4

• how do you test for group 2 ions using sodium hydroxide?

  1. Place 10 drops of 0.1 moldm-3 barium chloride in a clean test tube.

  2. Add 10 drops of 0.6 moldm-3 sodium hydroxide solution, mixing well and recording any observations. Must be clean to ensure a clear test result.

  3. Continue to add this sodium hydroxide solution, dropwise with gentle shaking, until in excess. Record any observations.

  4. Once completed, dispose of the contents by placing the test tube in a bowl of water. Repeat this test with the calcium bromide, magnesium chloride and strontium chloride
• describe what you would observe with dilute and excess NaOH

  dilute NaOH:

  - barium - colourless solution

  - calcium - slight white ppt

  - magnesium - slight white ppt

  - strontium - slight white ppt

  
  

  excess NaOH:

  - magnesium - white ppt

  - rest remain unchanged
• how do you test for group 2 ions using sulphuric acid?

  1. Place 10 drops of 0.1 moldm-3 barium chloride in a clean test tube. Add 10 drops of 1.0 moldm-3 sulfuric acid, mixing well and recording any observations.

  2. Continue to add this sulfuric acid, dropwise with gentle shaking, until in excess.

  3. Once completed, dispose of the contents by placing the test tube in a bowl of water. Repeat this test with the calcium bromide, magnesium chloride and strontium chloride.
• what would you observe with dilute and excess H2SO4?

  dilute H2SO4:

  - barium - white ppt

  - calcium - slight white ppt

  - magnesium - slight white ppt

  - strontium - white ppt

  
  

  excess H2SO4:

  - magnesium - colourless solution

  - rest remain unchanged
• how do you test for ammonium ions?

  1. Place 10 drops of ammonium chloride into a clean test tube. Add about 10 drops of sodium hydroxide solution. Shake the mixture.

  2. Warm the mixture in the test tube gently using a water bath. (necessary because ammonia gas is very soluble)

  3. Test the fumes released from the mixture by using forceps to hold a piece of damp red litmus paper in the mouth of the test tube.

  4. Dispose of the contents by placing in a test tube full of boiling water

  5. Record the observation of the damp red litmus paper (should turn blue).
• how do you test for hydroxide ions in aqueous solutions?

  1. Test a 1 cm depth of solution in a test tube with red litmus paper or universal indicator paper.

  2. Record your observations. Dispose of the test tube contents.

  3. Sodium hydroxide will turn damp red litmus paper blue.
• how do you test for hydroxide ions in ammonia?

  1. Take 5 drops of 1.0 moldm-3 ammonia solution and place on a filter paper and place inside a petri dish with lid.

  2. Dampen a piece of red litmus paper with deionised (distilled) water and place on the other side of the petri dish.

  3. Replace the lid and observe over a few minutes.

  4. Ammonia solution vapours will turn damp red litmus paper blue
• how do you test for carbonate ions?

  1. Add an equal, small volume of dilute hydrochloric acid to sodium carbonate solution in a test tube.

  2. Use a delivery tube to transfer the gas produced into a second test tube containing a small volume of calcium hydroxide solution (limewater).

  3. Put a stopper into the test tube containing the calcium hydroxide solution (limewater).

  4. The limewater will go cloudy if carbonate ions present.
• give equations to show the overall test for carbonate ions?


  Na2 CO3 + 2HCl → 2NaCl + H2 O + CO2

  Ca(OH)2 + CO2 → CaCO3 + H2 O
• how do you test for sulphate ions?

  1. Add an equal volume of dilute hydrochloric acid then an equal volume of barium chloride solution to the solution.

  2. Barium sulphate formed (white precipitate).

  3. Add a small volume of dilute HCl.

  4. As precipitate does not dissolve, sulphate or hydrogensulfate ions are present.
• give an equation to show the overall test for a sulphate ion?

  MgSO4 + BaCl2 → BaSO4 (s) + MgCl2 (aq)
• how do you test for halide ions?

  1. Add a small volume of dilute nitric acid to the solution of potassium chloride.

  2. Add 2 cm of silver nitrate to the solution. Record any observations.

  3. Swirl the tubes to ensure that the precipitates formed in each case are evenly distributed and then divide the contents of each tube in half.

  4. To one half of the contents, add an excess of dilute aqueous ammonia solution and observe what happens. Record your observations.

  5. To the other half, working in a fume cupboard, add an excess of concentrated ammonia solution and observe what happens. Record your observations.

  6. Repeat with solutions of potassium bromide and potassium iodide in new, separate test tubes
• what would you observe with silver nitrate and halide ions?

  Cl- : white ppt

  Br-: cream ppt

  I-: yellow ppt
• how would you further test the ppt produced with dilute and excess ammonia?

  dilute ammonia:

  Cl-: ppt dissolves so colourless solution

  Br-: cream ppt

  I-: yellow ppt

  
  

  excess ammonia:

  Cl-: ppt dissolves colourless solution

  Br-: ppt dissolves so colourless solution

  I-: yellow ppt
• what are some safety precautions for testing halides?

  ● Concentrated ammonia is corrosive so chemical splash-proof eye protection and nitrile gloves should be worn.

  ● Use a fume cupboard.

  ● Dilute nitric acid is an irritant.
• What is the order of testing ions? (Carbonate, halide and sulphate)

  Carbonate -> sulphate -> halide

  This prevents false positive results occurring i.e. unexpected insoluble precipitates
• how do you test for group 2 ions using sodium hydroxide?

  1. Place 10 drops of 0.1 moldm-3 barium chloride in a clean test tube.

  2. Add 10 drops of 0.6 moldm-3 sodium hydroxide solution, mixing well and recording any observations. Must be clean to ensure a clear test result.

  3. Continue to add this sodium hydroxide solution, dropwise with gentle shaking, until in excess. Record any observations.

  4. Once completed, dispose of the contents by placing the test tube in a bowl of water. Repeat this test with the calcium bromide, magnesium chloride and strontium chloride
• describe what you would observe with dilute and excess NaOH

  dilute NaOH:

  - barium - colourless solution

  - calcium - slight white ppt

  - magnesium - slight white ppt

  - strontium - slight white ppt

  
  

  excess NaOH:

  - magnesium - white ppt

  - rest remain unchanged
• how do you test for group 2 ions using sulphuric acid?

  1. Place 10 drops of 0.1 moldm-3 barium chloride in a clean test tube. Add 10 drops of 1.0 moldm-3 sulfuric acid, mixing well and recording any observations.

  2. Continue to add this sulfuric acid, dropwise with gentle shaking, until in excess.

  3. Once completed, dispose of the contents by placing the test tube in a bowl of water. Repeat this test with the calcium bromide, magnesium chloride and strontium chloride.
• what would you observe with dilute and excess H2SO4?

  dilute H2SO4:

  - barium - white ppt

  - calcium - slight white ppt

  - magnesium - slight white ppt

  - strontium - white ppt

  
  

  excess H2SO4:

  - magnesium - colourless solution

  - rest remain unchanged
• how do you test for ammonium ions?

  1. Place 10 drops of ammonium chloride into a clean test tube. Add about 10 drops of sodium hydroxide solution. Shake the mixture.

  2. Warm the mixture in the test tube gently using a water bath. (necessary because ammonia gas is very soluble)

  3. Test the fumes released from the mixture by using forceps to hold a piece of damp red litmus paper in the mouth of the test tube.

  4. Dispose of the contents by placing in a test tube full of boiling water

  5. Record the observation of the damp red litmus paper (should turn blue).
• how do you test for hydroxide ions in aqueous solutions?

  1. Test a 1 cm depth of solution in a test tube with red litmus paper or universal indicator paper.

  2. Record your observations. Dispose of the test tube contents.

  3. Sodium hydroxide will turn damp red litmus paper blue.
• how do you test for hydroxide ions in ammonia?

  1. Take 5 drops of 1.0 moldm-3 ammonia solution and place on a filter paper and place inside a petri dish with lid.

  2. Dampen a piece of red litmus paper with deionised (distilled) water and place on the other side of the petri dish.

  3. Replace the lid and observe over a few minutes.

  4. Ammonia solution vapours will turn damp red litmus paper blue
• how do you test for carbonate ions?

  1. Add an equal, small volume of dilute hydrochloric acid to sodium carbonate solution in a test tube.

  2. Use a delivery tube to transfer the gas produced into a second test tube containing a small volume of calcium hydroxide solution (limewater).

  3. Put a stopper into the test tube containing the calcium hydroxide solution (limewater).

  4. The limewater will go cloudy if carbonate ions present.
• give equations to show the overall test for carbonate ions?


  Na2 CO3 + 2HCl → 2NaCl + H2 O + CO2

  Ca(OH)2 + CO2 → CaCO3 + H2 O
• how do you test for sulphate ions?

  1. Add an equal volume of dilute hydrochloric acid then an equal volume of barium chloride solution to the solution.

  2. Barium sulphate formed (white precipitate).

  3. Add a small volume of dilute HCl.

  4. As precipitate does not dissolve, sulphate or hydrogensulfate ions are present.
• give an equation to show the overall test for a sulphate ion?

  MgSO4 + BaCl2 → BaSO4 (s) + MgCl2 (aq)
• how do you test for halide ions?

  1. Add a small volume of dilute nitric acid to the solution of potassium chloride.

  2. Add 2 cm of silver nitrate to the solution. Record any observations.

  3. Swirl the tubes to ensure that the precipitates formed in each case are evenly distributed and then divide the contents of each tube in half.

  4. To one half of the contents, add an excess of dilute aqueous ammonia solution and observe what happens. Record your observations.

  5. To the other half, working in a fume cupboard, add an excess of concentrated ammonia solution and observe what happens. Record your observations.

  6. Repeat with solutions of potassium bromide and potassium iodide in new, separate test tubes
• what would you observe with silver nitrate and halide ions?

  Cl- : white ppt

  Br-: cream ppt

  I-: yellow ppt
• how would you further test the ppt produced with dilute and excess ammonia?

  dilute ammonia:

  Cl-: ppt dissolves so colourless solution

  Br-: cream ppt

  I-: yellow ppt

  
  

  excess ammonia:

  Cl-: ppt dissolves colourless solution

  Br-: ppt dissolves so colourless solution

  I-: yellow ppt
• what are some safety precautions for testing halides?

  ● Concentrated ammonia is corrosive so chemical splash-proof eye protection and nitrile gloves should be worn.

  ● Use a fume cupboard.

  ● Dilute nitric acid is an irritant.
• What is the order of testing ions? (Carbonate, halide and sulphate)

  Carbonate -> sulphate -> halide

  This prevents false positive results occurring i.e. unexpected insoluble precipitates