Acids and pH Values:

[TOGWT]

Acids and pH:
What is pH and what does it mean?
Simply put the pH scale is a set of numbers between 0 and 14 where 0 is the most acidic and 14 is the most alkaline (caustic) with 7 in the middle, being neutral. Conceptually, since most people in our industry are interested in the acid side of the system, the smaller the number, and the more acidic the system.

Unfortunately the scale is logarithmic, for every integer that the scale decreases the material is 10 times more acidic. Those of us in earthquake country know all too well the consequences of a change of from 6 to 7 on the logarithmic, Richter scale. The difference in the pH scale is just as dramatic and therefore just as misleading.

A few examples of maximum acid strength might be helpful:
Sea water has pH of 7.75 to 8.25
Tap water has a pH of between 5.5 and 6.5.

Organic acids
Citric acid, found in citrus fruits has a pH of 2.0
Oxalic acid, found in spinach has a pH of 1.8

‘Weak’ mineral acids
Phosphoric acid has pH of 2.2
Hydrofluoric acid has a pH of 3.14

‘Strong’ mineral acids
Sulphuric acid, battery acid, has a pH of .32 @ 1N (indicates concentration)
Hydrochloric acid, aka Muriatic acid has a pH of 0.1 @ 1N.

A couple of things to note from this list are a) how very strong ‘strong acids’ are
b) How relatively weak yet dangerous hydrofluoric acid is and
c) And how small and misleading the difference is between organicacids and weak mineral acids. As an example, hydrofluoric acid (HF), one of the most highly regulated, most dangerous acids and the only acid that will dissolve glass is a weak acid. Also, these numbers are maximums, the pH increases when the solution is diluted or changes when there are other substances are dissolved in the solution.

Just to complicate things a bit more, mixing some strong mineral acids together with other relatively weak acids can create a solution of "super acid". This can result in acid strengths of up to 12 times higher than either acid by itself and are not measured accurately by the normal pH scale. In theory, this is the result obtained by adding HF to other mineral acids in wheel cleaners. Or mixing several weak acids together can have a synergistic effect where together these acids do more than just strong solutions of each one separately.

In practical applications, a formulator can get identical pH values by using various quantities of different acids. For example very small amounts of very strong acids or larger amounts of weaker acids can result in the same pH. But since pH is not a very good indicator of the strength of the acid in every system, this approach won't always produce the desired results. Each acid has properties that make it most useful for certain jobs. For example Citric acid is quite good at picking up Calcium ions in solution so acts as a good water softener where the same pH of a Sulphuric acid solution would be worthless for that application. My point here is that, it is not possible to judge how well a product will do the job it is designed for just by measuring the pH and stronger is not always better.

So, acid strength is always relative to the system you’re measuring and what materials are in danger of being dissolved or attacked by the acid pH is a measure of the relative strength of an acid but the key word is relative.
(See also Potential of Hydrogen – pH, Hydrofluoric Acid)

Information resource -http://en.wikipedia.org/####/Hydrofluoric_acid
Index to Hyper Physics- pH as a Measure of Acid and Base Properties
Material Data Sheet - MSDS - http://www.jtbaker.com/msds/englishhtml/H3880.htm

© 2004 – 2007 all rights reserved - Jon Miller aka TOGWT™

[Thejoyofdriving]

Do you know what the PH of concentrated nitric acid is?

[TOGWT]

Seems a very strange question in relation to a thread like this, but then as the question comes from TJD I 'gotta ask, what are you going to do with Nitric acid?

HNO3 Nitric acid pH 1.0

[Thejoyofdriving]

Originally Posted by TOGWT

Seems a very strange question in relation to a thread like this, but then as the question comes from TJD I 'gotta ask, what are you going to do with Nitric acid?

HNO3 Nitric acid pH 1.0

Oh, just using it as a gentle wheel cleaner(JK, no one try that, you wont have any wheels left) No, I was wondering because I have some lab grade Hydrochloric acid, Sulfuric acid, and Nitric acid and last time I played around with them the Nitric acid seemed to be the strongest, and I liked it the most as it gave off a nice fruity sent(JK, dont breath in the fumes comming off acids, very deadly, just making sure some one doesnt go "hey cool I didnt know that, im going see for my self"). Kinda of topic but was just wondering. Do you know by any chance what the PH of carbonic acid is, not concentrated, but like the naturaly uccuring carbonic acid like in rain? Also would you happen to know what the most common acid found in wheel cleaners is? Sorry for all the questions, theres just so much I could learn from you!

[TOGWT]

Nitric acid is often used to 'burn' old tree stumps

Acid rain Once ozone, water and industrial fall out (IFO) become mixed together and heat is added it becomes acid rain, (sulphuric dioxides) the pH of rainwater; Pure-7.0, Normal 5.5, Acid rain 3.5-4.0.

[Thejoyofdriving]

Originally Posted by TOGWT

Nitric acid is often used to 'burn' old tree stumps

Acid rain Once ozone, water and industrial fall out (IFO) become mixed together and heat is added it becomes acid rain, (sulphuric dioxides) the pH of rainwater; Pure-7.0, Normal 5.5, Acid rain 3.5-4.0.

Wouldn't rain water always have carbonic acid in it, because it mixes with the CO2 with the air, thus always giving it a PH below 7.0?