Vinegar and baking soda

Vinegar and baking soda are two commonly used ingredients in cooking. When combined, they form a useful cleaning product. These products, alone or together, have a low toxicity to humans and are derived through processes which are not unduly harmful to the environment.

The production of carbon dioxide by mixing baking soda and vinegar is of great utility when cleaning. Tiny bubbles allow you to "scrub" down inside of little imperfections of the surface you wish to clean. Hydrogen and acetate anions will act as a exchangers and surfactants, releasing bound materials.

Try this: coat a cutting board with baking soda, rub it into the cuts in the surface and pour a bit of vinegar on it. Often times, you will notice that material which is trapped within the knife marks in the board will be liberated by the fizzing. You can keep adding vinegar until all of the baking soda has been consumed, as the acidity of vinegar is neutralized by baking soda over time causing the CO2-producing reaction to proceed less vigorously as the pH increases.

Vinegar
Vinegar is a product of fermentation of organic materials. White vinegar is a distillation product (purified form) of vinegar. White vinegar is often standardized to be 5% by mass acetic acid. Acetic acid is a weak acid which means it does not completely dissociate in water.

That is the reaction: CH3COOH <-> CH3COO- + H+ does not proceed all the way to the right.

The pKa of acetic acid is about 4.76. With 5% acetic acid by mass this yields a pH of approximately 2.4 which is fairly acidic.

For comparison: Pure water has a neutral pH of 7. Natural water (in equilibrium with the atmosphere) has a pH of approximately 5.6, due to the presence of dissolved carbonate, sulfate and nitrate. The tap water (from the nearby pumping station) here at the farm has been corrected from its natural range (pH ~=5) to just above pH 7, using sodium hydroxide. This allows dissolved iron containing minerals to be removed from the line before being pumped towards campus, where if left unchecked they can clog pipes and fixtures and the low natural pH can induce corrosion.

Low pH can be toxic to many microorganisms. However, organisms which are able to form protective biofilms, encyst (form a protective coat and go dormant) or tolerate low pH may not be affected by vinegar.

Baking Soda
Baking soda is a carbonate salt comprised of sodium (Na+) and bicarbonate (HCO3-).

Carbonates result from the dissolution of carbon dioxide in water, forming carbonic acid. Carbonic acid readily undergoes pH dependent reactions to form bicarbonate and carbonate anions.

e.g. H2O + CO2 <-> H2CO3 <-> HCO3- + H+ <-> CO32- + H+

If you add an acid (H+) to water with carbonates in it, the above reaction will be pushed to the left. If you add a base (OH-) the reaction will be pushed to the right, shifting the dominant dissolved carbon species towards carbonate (see Le Chatlier's Principle).

If the series of equilibrium reactions above are pushed to the left, carbon dioxide (CO2) gas will be produced. This is why when you add vinegar to baking soda or vice versa the mixture is highly effervescent (fizzes).

Precautions
It is generally not a good idea to mix bleach with vinegar. If you are going to use both bleach and vinegar to clean, use them separately. The low pH of the vinegar will increase the production of chlorine gas, which may enhance the cleaning power but you may find yourself with a lungful of chlorine. This is not nice. Vinegar and baking soda mixtures will spatter as they effervesce carbon dioxide gas, with bleach in the mixture it is possible that you could get spattered with bleach. Also not nice.