ChemixaLEARN CHEMISTRY

Baking soda and vinegar neutralization

Objective: observe an acid-base neutralization reaction between household baking soda and vinegar, and track how the acidity of the mixture changes as the reaction proceeds. You will measure, mix, and use a simple indicator to confirm the chemistry.

Safety:

Never seal the mixture in a closed bottle: the carbon dioxide pressure can burst the container. Wear eye protection or keep your face back from the fizzing cup. Adult supervision is required for minors. Do not drink the mixture.

Materials

  • Baking soda
  • White vinegar
  • Two clear cups
  • Measuring spoons
  • Red cabbage indicator or pH paper (optional)
  • Stirring stick

Procedure

1

Prepare the acid

Pour about half a cup of white vinegar into a clear cup and note its smell and appearance.

2

Test the starting pH

If you have indicator, add a few drops and record the color as your starting point.

3

Add the base

Add one tablespoon of baking soda to the vinegar and watch immediately.

4

Watch the reaction finish

Stir gently and observe the fizzing until it completely stops.

5

Test the final pH

Test the final mixture with indicator again and compare the color with your starting reading.

6

Compare before and after

Smell the mixture cautiously from a distance and note how it changed.

What to observe

  • Bubbles and foam erupt as soon as the two mix.

  • Fizzing slows and stops after a minute or two.

  • The vinegar's sharp smell fades in the mixture.

  • Indicator shows the mixture is far less acidic than the starting vinegar.

Why it happens

Baking soda is sodium bicarbonate, a base, and vinegar is a dilute solution of acetic acid. When they meet, the acid donates a proton to the bicarbonate ion, forming carbonic acid, which immediately breaks down into water and carbon dioxide gas: NaHCO3 + CH3COOH -> CH3COONa + H2O + CO2. The fizzing is carbon dioxide escaping. If you test the liquids with indicator before and after, you can watch the pH move: the vinegar starts acidic, and as the base neutralizes the acid, the mixture becomes much less acidic. When the fizzing stops, the reaction is complete because one reactant has run out.

Try variations

  • Change the amount of baking soda and see how long the fizzing lasts.

  • Try lemon juice instead of vinegar and compare the vigor.

  • Add the vinegar slowly in spoonfuls and test the pH after each addition.