In a large mixing cup, stir together the baking soda and water until the baking soda is dissolved.
Stir in the red food colouring.
Pour the mixture into the heart-shaped silicone mould and freeze overnight or until completely frozen.
Place the mould on a large shallow dish.
Carefully squeeze over vinegar a small amount at a time.You could also pour the vinegar into the shallow bowl, then carefully lower the frozen heart into the vinegar. If doing this method, I recommend having an adult lower the heart while wearing a pair of gloves.
Keep adding vinegar and watch what happens.
As the vinegar reactions with the baking soda, the heart will slowly melt away.
The more vinegar you add, the more the heart dissolves.
Additional Experiment Ideas
* Create frozen hearts using a solution made from vinegar and water. Dip the frozen hearts into a solution of baking soda and water.
* Experiment with different ratios of baking soda to water when freezing the hearts to see which brings a more exciting reaction.