Chemical Forums
Specialty Chemistry Forums => Other Sciences Question Forum => Topic started by: Tvolpe on March 27, 2014, 03:22:41 PM

Hi everyone. Newbie here to this forum. I have an issue I've been racking my brains out with. How do you determine the volume percent of a nitric acid solution. I know how to titrate to get the answer in weight percent but the conversion from weight percent to volume percent is somehow eluding me.
If I titrate with a known volume of 1N NaOH and a know volume of nitric acid solution is there a formula that gets me directly to volume percent of nitric.
Thanks!!! ???

You need to know the density for the conversion, but even then the answer is ambiguous.
When you mix 50 mL of water and 50 mL of pure sulfuric acid, you get 91.3 mL of the solution. Is it 50% in sulfuric acid, or 54.8%? And if it is 54.8% in sulfuric acid, it is also 54.8% in water, does it mean it has 109.6% of components in total?

It is confusing because in some cases the sum of the parts doesn't equal the whole. I read that if you mix 50 liters ethanol and 50 liters of water you total won't be 100 liters because of a reaction between the ethanol and the water.
I know the density for 67% Nitric acid is 1.512g/cc. But that is not helping me. I can figure out the molarity of the solution but that is where I get stuck. I have been calculating the weight percent of the solution per ASTM E1584 but come to find out that AMS 2700 call out the concentration in Volume percent hence my dilemma.

I apologize for the late reply. Calculating volume percentage (φ) is tricky because, as you pointed out, volumes of species with differing densities are not additive. Taking volume (V) as equal to mass (m) divided by density (ρ), the volume ratio of the solute to the solution is
φ_{solute} = (V_{solute}/V_{solution}) = [(m_{solute}/ρ_{solute})/(m_{solution}/ρ_{solution})]
where the solute is HNO_{3} as a pure substance and the solution is nitric acid.
Simplifying,
φ_{solute} = (ρ_{solution}/ρ_{solute})ω_{solute}
where ω is the mass fraction of the solute.
Given ω, the data additionally needed are the density of the pure substance and the solution, both of which can be found in Perry's Chemical Engineers' Handbook. Nitric acid solution densities are available at a wide range of temperatures and mass percentages, but the density of pure HNO_{3} is provided only at 20°C (I was not able to find the density of the pure substance at other temperatures). Kindly note that the density you provided (1.512 g/ml) represents the pure substance and not the 67% solution by weight. Because φ varies with temperature, the calculation with temperatures beyond 20°C will lose accuracy.