Why does baking soda and vinegar remove stains?

Question

To remove a stain on fabric, I often rub baking soda into the stain, and then sponge it with white vinegar. This causes a chemical reaction, involving some fizzing and frothing, and once the fabric has dried, the stain (hopefully) has disappeared. Why does this chemical reaction remove the stain?

From my basic knowledge of chemistry, I know this is a classic Acid + Base -> CO2 + H2O + Others. But this doesn't involve the chemicals which have caused the stain.

Is it that these chemicals also react, and turn into other colourless products? Or is it that the frothing action from the reaction just dislodges these chemicals, allowing them to more easily be wiped clean? Or is there another answer?

Answer 1

You might try a comparison test to see if baking soda and vinegar is any more effective than plain water, or water and one of the ingredients. There are some possible reasons why each might be effective:

• Some dyes and stains are set by exposure to acid, such as vinegar, which makes them harder to remove. It is possible that alkaline baking soda and water have the opposite effect, removing the stain.

• Some stains, such as from red cabbage and red wine, are indicators, and change color when exposed to alkali or acid. The natural dye alizarin changes from dark red to lighter yellow under acid conditions, as in vinegar.

• A powder such as baking soda may act as a sponge or adsorbent because of its large surface area. Talcum powder, baking soda or fuller's earth are also used for that purpose.

• There might be a physical effect from the bubbles, as you state. For that reason, perhaps, some use plain seltzer (carbonated water) for stain removal.

Note that there are many conflicting statements on the efficacy of these stain removal techniques. It would be of benefit to humanity if someone conducted controlled experiments on removing a variety of stains with these chemicals! In the meantime, I just put a bit of HE laundry detergent on a stain, or a commercial cleaner such Lestoil, on the spot, before laundering.

Answer 2

From what I have read on stain and odor chemistry, the active chemical that creates a stain or odor is usually acidic or alkaline in nature. Baking soda is a weak base and can act like a buffer. Vinegar is a weak acid and can act like a buffer also. Using an alkaline compound on an acidic stain should remove that stain. Acid on an acid stain should set it. Using both alkaline and vinegar should remove most stains that are acidic or alkaline. If you encounter a stain or dye that cannot be removed with alkaline or acidic compounds, oxidizers that use oxygen like bleach or peroxide can also work. Surprisingly some stains can be removed with just warm or hot water.