acid

Sulphuric acid has a pKa value over 6 below that of citric acid - which means it would have to be diluted enormously (somewhere between 10,000 and one million times) to have the same pH. It would become exhausted very rapidly at this concentration.

In practice, something around 10% should work fine - but be aware it can, even at this concentration, be very irritating to skin and damaging to eyes; it can also destroy fabric over time as it becomes concentrated through evaporation.

I have found sulphuric acid quite easy to buy from jewellers' suppliers - though you may need to sign a book stating the purpose for which you want it ("pickling" should be fine). It was a few years ago though, so it's possible things have changed. I honestly would not recommend anyone to buy/use concentrated sulphuric acid unless you know what you are doing - your point about *always* adding acid to water is bang on, but also bear in mind that so much heat is generated that the solution can boil. Either do it gradually with intervals to cool, or add acid to ice.

Citric acid is readily available through Amazon or eBay.

David

Edited By David Littlewood on 04/11/2013 19:36:55

Just one observation- if you put a cambden tablet ( sodium metabisulphite into citric acid it evolved SO2 ( which is not nice, odourless but toxic ( makes you cough like blazes and get a tight chest) In answer to the question don't worry about the mould as long as the acid work. It's amazing what bugs can live on. If you keep the caitric acid stock dryu until you need it it should not be an issue. Once it's wet and in use, mould will (eventually ) grow. Like toast always falls buttered side down- nature has a way of getting to you!

Sulphuric is faster but citric is safer!

Regards Ian

SO2 isn't very odourless in these parts!

Neil

Too much curry perhaps Neil?

I just know from home brewing days ( still got gallons in the store) that although cambden tablet plus citric cleans and sterilizes quicker the coughing fits and watering eyes weren't worth the increased speed. Better to learn from others coughing than smell it your self?

Regards Ian