Vinegar

• Vinegar is a common acid that is found in most kitchens. Its scientific name is acetic acid, and it's pH level is 3. To cause a chemical reaction between vinegar and baking soda, mix a few teaspoons of baking soda in a glass half-filled with water. Pour a spoonful of vinegar into the glass. The vinegar will react with the baking soda and a foam will form. This reaction will create water, salt and carbon dioxide gas.
  
  

Lemon Juice

• Lemon juice, a citric acid, has a pH level of 2. When combined with baking soda, it will react similarly to vinegar, forming a foam and producing water and carbon dioxide as well as a small amount of sodium citrate. For a visual demonstration of this reaction, first combine a teaspoon of baking soda with a teaspoon of dish soap in a small cup. Squeeze some lemon juice into the cup and gently stir. Soapy suds will begin to bubble up in the cup. This sudsy mixture can be used to clean a dirty surface or dish, just as you would use dish soap.
  
  

Hydrochloric Acid

• Hydrochloric acid has a pH level of 0, making it a highly corrosive acid. It is best to use hydrochloric acid in a diluted form, and then only in a laboratory setting with appropriate safety equipment. As an acidic substance, it will react when combined with baking soda. When combined, hydrochloric acid and baking soda form carbonic acid. This acid quickly bubbles away, producing water and carbon dioxide gas.
  
  

Rainwater or Tapwater

• Pure water has a pH of 7, making it a neutral substance, exactly between bases and acids. However the water that falls as rain, and in many cases the water that comes from your kitchen faucet, is slightly more acidic than pure water. Since the pH is not as low as stronger acids, the reaction with baking soda will not be quite as dramatic, but combining some rainwater with baking soda should cause some bubbling to occur. This reaction will neutralize the acidic water while releasing some carbon dioxide.