• 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.