# Calculating molarity of a gas using ideal gas equation

Is hydrogen gas at 1 atm pressure and 298 K temperature considered as a 1 molar solution? If yes then can I use ideal gas equation $$PV=nRT$$ to find molarity as $$\frac nV = \frac P{RT}?$$

• I get confused after reading the following paragraph .The standard hydrogen electrode consists of a platinum electrode coated with platinum black. The electrode is dipped in an acidic solution and pure hydrogen gas is bubbled through it. The concentration of both the reduced and oxidised forms of hydrogen is maintained at unity (Fig. 3.3). This implies that the pressure of hydrogen gas is one bar and the concentration of hydrogen ion in the solution is one molar. so I asked the question. It is Said that concentration of redox couple should be one for finding standard potential – JM97 Dec 18 '15 at 7:23
• Oh sorry, that homework part was not supposed to be there. But if you have questions that tend to go in that direction, then it's good if you know about the policy anyway. – Martin - マーチン Dec 18 '15 at 7:25

## 1 Answer

Hydrogen at one atmosphere pressure and 298 K is certainly not a one molar solution. However, you can still calculate the concentration with the ideal gas. Note that this is a gaseous solution and since it is a pure gas, the solute is also the solvent. $$c(\ce{H2}) = \frac{n(\ce{H2})}{V(\ce{H2})} = \frac{p(\ce{H2})}{\mathcal{R}T} \approx 40.9~\mathrm{mol\,m^{-3}} \approx 0.04~\mathrm{mol\,L^{-1}}$$

• So it means that 0.04 molL-1 of hydrogen gas at equilibrium with one molar H+ ion solution will give standard electrode potential – JM97 Dec 18 '15 at 7:33
• Not quite, see wikipedia for the set-up of the standard hydrogen electrode. If you have any more questions about that, you should consider asking a new question: How to Ask. – Martin - マーチン Dec 18 '15 at 7:44
• I am unable to understand the folowing statement of Wikipedia :The concentration of both the reduced form and oxidised form is maintained at unity. That implies that the pressure of hydrogen gas is 1 bar – JM97 Dec 18 '15 at 9:29
• @JawadMirza you should ask a new question, the SE system works better this way. Anything we resolve in the comments won't benefit other users. – Martin - マーチン Dec 18 '15 at 12:57