Moles

[lillylemon]

how does 5 moles of nitric acid relate to 2.5 moles of nitric acid?

[boxtops]

twice as much?

[Calibax]

^Yep!

[theprof]

First of all, find the molar mass of nitric acid. This will provide you with the volume of nitric acid in a 1M solution. Multiply that figure as appropriate and then compare the resultant figures. The answer should be obvious.

[Tim123]

5 moles of nitric acid is twice as many molecules of HNO3 as 2.5 moles. One mole of a substance contains about 6.02x10^23 'elementary entities' - molecules in this case. That figure is known as the Avogadro constant.

Lab acid is normally a 1M solution, which means there are 6.02x10^23 molecules of HNO3 in every litre of solution. The concentrated stuff that you need to handle with extreme caution may be 5M, with 3.01x10^24 molecules of HNO3 per litre of solution.

[theprof]

Eh? "Lab acid is normally a 1M solution". No, Tim123. There is no such thing as lab acid as you put it. It all depends on the application. In addition, bench acids are not necessarily 1M either.

All research and teaching laboratories carry a wide range of acid at various molarities for the purposes undertaken.

5M HNO3 is indeed corrosive, but I've seen nasty burns from a 1M solution which is why most laboratories label 1M and above as corrosive. A more dilute solution below 1M is normally labelled as an irritant.

[pcbpage]

Well, to soothe Tim123's ruffled feathers, bench top dilute nitric acid that you might typically find in a chemistry lab like mine would commonly be 1M or 2M. But, as theprof says, there's no rule, and a lab using it a lot might well have a range of concentrations available, made up to suit their purposes. The most common grade of commercial concentrated nitric acid is around 68% (it's an azeotrope), which I think is around 15 M, but there are of course a number of grades available.