What you will need:
• Grape Juice
• Vinegar
• Bicarbonate of soda
• Spoon
• Tray / Plate
• Glass cup

What to do:
Place the glass cup in the centre of a tray. Pour about a ¼ cup of grape juice into the glass with an equal amount of water. Add ½ a spoon of bicarbonate of soda. Stir well. Do you notice any change? Now add ½ cup of vinegar. Stir well.

What to look out for:
The grape juice, with the water added, has a reddish-pink colour (see glass 1 in photograph). When the bicarbonate of soda was added, which is a weak base, the grape juice change a dark, almost black colour (see glass 2 in photograph). When vinegar, which is a weak acid, the coloured reverted back to pink (see glass 3 in the photograph). The grape juice is acting as an indicator which is pink in an acidic solution and black in a basic solution.