June Wong, of Wellington, asks :-

I use a Baking Soda and White Vinegar cleanser to a recipe of 2Tb Baking Soda, 1 cup of white vinegar and brought up to 1 litre of water. My use is mainly for surfaces in the kitchen.

How effective is this cleanser for bathrooms and toilets and pet toilets where there are more virulent micro organisms?

I have read that people use baking soda and vinegar (undiluted) to clean toilets, and I believe the cleanser is used in kindergardens and day care centres. How do we know if it's killing germs ?

Alan Happer, a chemist at the University of Canterbury, responded.

My belief has always been that the main reason that baking soda (sodium bicarbonate) is used as a cleanser in the home these days is that the user’s mother and, her mother in turn both swore by it. However in their case the available selection of cleansers at the time was relatively limited. Furthermore there was usually some baking soda in the kitchen cupboard somewhere. Sodium bicarbonate is a cheap chemical, but I am not sure whether buying it in the form of ‘baking soda’ that this is true. It was used as a paste, as it’s cleaning value lay in this acting as a mild abrasive.

It is reasonably soluble in water (ca. 10g/100mL) and reacts readily with acids (vinegar contains about 5% acetic acid).

I suspect that the recipe used by the questioner would have little (if any) abrasive effect. (It might even be a clear solution and have none). I doubt whether such a solution would have any affect on bacteria at all. The acetic acid in the vinegar would have reacted with it to form sodium acetate and liberated CO2 gas. Ironically vinegar itself is quite a good bactericide/fungicide, but this could have been reduced or even eliminated altogether by the addition of the baking soda.

The sole advantage of using baking soda with or without vinegar in preference to commercial cleansers would appear to be be their well established lack of toxicity. They are nowhere near as effective at killing bacteria or other microorganisms, but on the other hand they are not as effective at harming young children if the latter get their hands on them. Unfortunately there is a tendency for cleaning products to be stored at low levels under the sink because more often than not that is close to where they will be mostly used.

The value of baking soda as a mild abrasive is less than it once was, because these days bench tops are more resistant to commercial ones that use silica as their abrasive. If the writer prefers to use baking soda and vinegar, however, it would make more sense to use them consecutively rather than at the same time.