The golden rule is alkali neutralises acid, and vice versa.
- Bicarbonate of soda is a powdered alkali. It's great for cleaning acidic stains. If you mix it with a little water to make a paste, it makes a very gentle scourer. Because the powder is very fine, it won't scratch like salt can.
- Vinegar is a solution of acid. It's good for cleaning alkali stains, and will dissolve greasy stains. I use it in a plant mister for cleaning surfaces, glass etc.
- If you add bicarb to vinegar the alkali neutralises the acid. A lot of carbon dioxide gas is released, and when the reaction is over you are left with a neutral liquid. Well, you probably had a bit too much of one or the other, so it will be a little bit acid or a little bit alkali - but there's no way of knowing which unless you measure precisely and understand the chemistry. Either way, the result has very little cleaning power. If a website or a book advises you to mix bicarb and vinegar, then the writer hasn't tested their own tips. I'd disregard everything else they say.
- Baking powder is a mixture of powdered bicarb and powdered tartaric acid. When dry, nothing happens, but mix them with liquid (e.g. in a cake batter) and they react. Carbon dioxide gas is released - that's what makes your cake rise. The acid neutralises the alkali. Baking powder is no use as a cleaning agent, but it does make great cakes. Again, anyone who recommends you use baking powder as a cleaning agent is confused. Be sceptical about taking their advice.
So that's the lowdown on bicarb and vinegar. They're very useful cleaning agents in their own right, but don't mix them unless you want to make a sink-top volcano for your 5-year-old to play with.
What other options are there for green cleaning?
- Soap is made by reacting a strong alkali with fat or oil. I make soap at home by reacting lye (sodium hydroxide - drain cleaner) with sunflower oil, coconut oil, olive oil etc. A lot of soap nowadays is made with palm oil, and there are all sorts of environmental problems with palm oil production, but that's a story for another day. The point is that soap is pretty environmentally benign and is a great cleaner. After all, it's what your granny used in the days before Cillit Bang.
- Hot water is a great asset to cleaning. Use rubber gloves and very hot water, a bit of soap and you can clean most things.
- Lemon juice is acidic and also a natural bleach, especially in combination with sunlight. But a commenter has pointed out that lemons in Britain have travelled a lot of food miles.
If all the cleaning products you owned were soap, vinegar, bicarb and a pair or rubber gloves, you could still keep your home as clean as you like.