![]() These reactions are effectively reversed in acid: Stand the phenolphthalein and copper sulfate flasks on white filter paper and the lead nitrate one on black paper for maximum impact. Scale the volumes up if the audience is some way away. ![]() In the final part of the demonstration the solution in the third flask may be very pale blue due to the copper ions, and there may be a few specks of undissolved lead hydroxide, but the audience is unlikely to notice this. Only the most sharp-eyed observers will notice even the pale blue colour of the copper sulfate in the third beaker before the demonstration begins. Pour the contents of the three beakers in turn into the nitric acid flask and the colours will disappear, leaving a clear, colourless solution in the flask.The levels of liquid in both flasks should by now be about the same. Now use some sleight of hand to switch the ammonia-containing flask with that containing the nitric acid.The phenolphthalein will turn red, the lead nitrate will form a milky white precipitate of lead(II) hydroxide and the copper sulfate will form the deep blue 2+ ion. Aim to leave the flask full to the mark at 125 cm 3. Pour about 40 cm 3 of ammonia solution in turn into each of the three beakers on the bench.Mark the ammonia flask at approximately the 125 cm 3 level.Place 250 cm 3 of ammonia solution in one 500 cm 3 flask and about 125 cm 3 of the nitric acid in the other.The volumes are not critical – a single ‘squirt’ from a teat pipette will be accurate enough. Place about 1 cm 3 of phenolphthalein solution in the first, about 1 cm 3 of saturated lead nitrate solution in the second and about 1 cm 3 of saturated copper sulfate solution in the third.Line up the three beakers on the bench.The following operations should be carried out of sight of the audience: Phenolphthalein solution (HIGHLY FLAMMABLE) – see CLEAPSS Hazcard HC032 and CLEAPSS Recipe Book RB000.Do not use tap water to make up the solution since it will turn cloudy if there are any chloride ions present. Add 14 g of lead nitrate to 10 cm 3 of deionised water and stir to make a saturated solution. Lead(II) nitrate solution, Pb(NO 3) 2(aq), (TOXIC, DANGEROUS FOR THE ENVIRONMENT) – see CLEAPSS Hazcard HC057a and CLEAPSS Recipe Book RB053.Copper(II) sulfate solution, CuSO 4(aq) – see CLEAPSS Hazcard HC027c and CLEAPSS Recipe Book RB031.Dilute nitric acid, HNO 3(aq), (CORROSIVE) – see CLEAPSS Hazcard HC067 and CLEAPSS Recipe Book RB061.Ammonia solution, NH 3(aq) – see CLEAPSS Hazcard HC006 and CLEAPSS Recipe Book RB006.All solutions must be made up in deionised or distilled water.Wear eye protection throughout and use protective gloves.Read our standard health and safety guidance.Phenolphthalein solution (HIGHLY FLAMMABLE).Lead(II) nitrate solution, saturated (TOXIC, DANGEROUS FOR THE ENVIRONMENT), 1 cm 3.Copper(II) sulfate solution, 0.5 M, 1 cm 3.Dilute nitric acid, 2 M (CORROSIVE), 250 cm 3.The demonstration lasts about three minutes, or longer if explaining the chemistry to a post-16 audience. It takes about 30–45 minutes to set up. Pouring the contents of the beakers into acid reverses the changes, to give a colourless solution. The beakers’ contents turn red, milky white and deep blue respectively. In this experiment, students observe what happens when a solution of ammonia is poured into each of three beakers, containing (unknown to the audience) small amounts of phenolphthalein, lead nitrate and copper(II) sulfate solution. RSC Yusuf Hamied Inspirational Science Programme.Introductory maths for higher education.The physics of restoration and conservation.
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