Squall181
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Determining the Concentration of Nitric Acid
Hi,
Recently I have been making nitric acid from KNO3 and sulfuric acid. I know that it is fuming nitric acid, but I would like to know more precisely
the concentration that I have. I have already determined the density and compared it to a chart I found somewhere on this site, but how accurate are
density measurements and I know I have some NO2 contamination since the acid is a light yellow color could this also throw my density measurement off.
I guess what I need to know is there a simple way to do a titration using household items or do I need a burret, an indicator and a standard solution.
Oh one more question I have read that the NO2 impurities can be removed by blowing dry air through the acid, just want to confirm if this is correct,
and if it is can I just pull air through a tube filled with calcium chloride and bubble it through the acid?
Thank You
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Magpie
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You could possibly titrate your acid with a weighed amount of baking soda (NaHCO3), using an eye dropper and a graduated cylinder. For an indicator
purple cabbage might work. I don't know the color change at neutrality but I would think that Google does.
The single most important condition for a successful synthesis is good mixing - Nicodem
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Squall181
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Thanks for the reply, this is actually what I had in mind, I've made cabbage indicator before, so I have some experience with its color changes. I
guess I will attempt this method and see if I can get any conclusive results. I will post the results when I'm done just in case anyone else wants to
try. Unfortunately that will be in a week or two when I return to my "lab".
BTW if anyone has done titration with purple cabbage as an indicator let me know what you think of it.
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Squall181
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Well its been a long time, but I've had time to titrate my sample of nitric acid. The titration was performed by mixing 1ml of nitric acid in about
50ml of water and then adding about a 1-2ml of red cabbage indicator to the solution. Next 30ml of 4M NaOH solution was prepared. It took on average
about 4.85ml of the NaOH solution to neutralize the acid. If my math is correct this means that my Nitric Acid has a molarity of about 19.4M.
Math: (4M)(4.85ml)=(M)(1ml)
M=19.4
On a side note the nitric acid was prepared in a coffee pot with saran wrap on top filled with ice. An insulated beaker was placed in the coffee pot
around which potassium nitrate and sulfuric acid were added. The whole setup was placed on a hot plate set on low. As gases began to evolve they
condensed on the surface of the saran wrap and dripped down into the beaker. I have successfully nitrated cotton with this acid and it seems to be of
a decent concentration according to my titration results.
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hissingnoise
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Saran is now composed of PE and is fairly resistant to HNO<sub>3</sub> but if you want the highest concentration possible treat yourself
to an all-glass set-up!
You'll end up wondering how you ever got along without it . . .
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Squall181
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Yeah I have my eye one some sets, but I'm not exactly sure what I need, condenser and adapter wise and I don't want to spend a lot of money and get
something that's not going to last. If anyone has suggestion on where to look for distillation kits or parts I would appreciate the advice, but yeah I
agree with you all-glass would be the best way to go if you have it, but this gives satisfactory results.
BTW when running the above set up I used a ball bearing help make a cone in the saran wrap and I noticed although the wrap is resistant to the fumes
some of the gas diffuses across the membrane and turns the cooling water acidic. I noticed this because the steel bearing began to give of small
bubbles and the water began turning brown.
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hissingnoise
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Timstar in the UK and UGT in the US!
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