Please ignore the "surfactant" remark, that was just me being pretentious (and inaccurate!) [

] What I really meant was a good foaming detergent, like washing-up liquid!

As for the pressure calculation:

A mole of a substance can be defined as its formula weight in grams (stricly speaking it's the weight of the same number of molecules as in 12 grams of carbon 12, 6.023 X 10^23, but life's to short for that stuff!).

The formula weight of sodium bicarbonate is the sum of the atomic weights of one sodium, one hydrogen, one carbon and three oxygens (approximately 23 + 1 + 12 + 48 = 84)

__which is where I got the 84 grams from.__When reacted with an acid, one molecule of sodium bicarbonate produces one molecule of carbon dioxide therefore one mole of the bicarbonate will produce 1 mole of carbon dioxide.

One mole of an

**ideal gas** (a gas in which all molecular collisions are elastic and there are no intermolecular forces)at standard temeperature and pressure (STP - 0 degrees C and one atmosphere pressure)would occupy a volume of 22.4 L (PV=nRT). That's a pretty good approximation for most gases,

__which is where I got the 20 L from__.

Obviously if you put the same amount of gas (1 mole) in a twentieth of the volume (1L), the pressure is twenty times greater (20 atm or about 300 psi or about 2000 kPa).

So there we are, not nearly as clever as I wanted people to think but probably roughly right [

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