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:
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