pH measurement, and how to fathom it.

jimr007March 31, 2006

I notice on some messages to this forum that some people are perplexed about pH, and how to fathom it.

Here is a thumbnail sketch that may help some people, without getting too technical.

Acids are acidic and low in pH. For example Sulphuric Acid and Hydrochloric Acid are highly acidic, whereas Citric Acid, Tartaric Acid and Acetic Acid are relatively weak acids, as are most organic acids.

Bases are alkaline and high in pH. Sodium Hydroxide (Caustic Soda) and Potassium Hydroxide are quite strong bases, whereas Sodium Carbonate (Washing Soda) is relatively weaker as an alkali. Ammonia is a moderately strong base.

It is important that you grasp the following concept as it should dissipate much of the mystery about pH measurement.

A pH of say 5.0 is TEN TIMES more acidic than a pH of 6.0

For all intents and purposes, a pH of 7.0 is regarded as neutral, i.e., neither acidic nor alkaline.

A pH of 10.0 is TEN TIMES more alkaline than a pH of 9.0

The pH scale is what is referred to as a Logarithmic Scale.

Now for pH meters. Please make sure you have a reliable pH meter and know how to calibrate it properly. If your pH drifts off too far, you will find that your plants are not growing as strongly as you would like them to. This has got a lot to do with the availability of Iron in solution.




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A few corrections. The pH is logrhythm base 10 or log10. A log can be any base, but for pH is base 10. The base 10 is not written as log 10 because 10 is a standard, whereas logrhythms with other numbers (i.e., log5) are written. It is because of the base 10 log we can say pH is ten times more or ten times less with each number in the wording.
Also, a pH of 5 is 10 times less acidic, not more. I made the same mistake when I wrote the FAQ, but was fortunate to have the input of a scientist when I wrote it.

    Bookmark   March 31, 2006 at 10:06AM
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Dear Baci,

Please go back to your books.
This was wriiten for the layman, but since you want to get technical, here it is:
pH is the "negative logarithm of the hydrogen concentration".

And a pH of 5.0 is still TEN TIMES more acidic than a pH of 6.0

And a pH of 4.0 is TEN TIMES more acidic than a pH of 5.0

I suggest you consult your "scientist" again.


    Bookmark   March 31, 2006 at 6:15PM
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I understand what you are saying, but pH is based on a decreasing number, which is where the wording I used came in. I will not negate the wording of one of the few GW contributors to the FAQ, but I can contribute contrary wording of those who disagree with the wording.
At issue is not disagreement with your words. I value those that come here to contribute to the GW forum, which is why I will not change his wording.
I also value when you contribute information to the GW forum, jimr007, for you offer an unique perspective on hydro growing.

    Bookmark   April 1, 2006 at 6:44AM
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Dear Baci,

I have managed to find your FAQ page and have read right through it. Basically, it is correct except for two minor errors. These are explained below.

The element "Phosphorus" is spelled this way right around the world. It does not have three letters "o" in it.

The piece you have about pH reads in part:
"A solution of pH = 8 is ten times more basic than one at pH = 7". This is correct.

"A solution at pH = 5 is ten times less acidic than one at pH = 6". This is NOT CORRECT.

It should read:

"A solution at pH = 5 is ten times MORE acidic than one at pH = 6".

What I suggest you do ... is fix these two errors (and they are errors, I assure you) before they mislead anyone else. If you still have doubts about what I have suggested above, please consult a qualified chemist.


    Bookmark   April 2, 2006 at 7:18AM
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I thought about the post over night, & think there is still some confusion in the wording.

The use of the word "less" in my wording was to imply the inverse nature of the pH scale, not the strength of the acid. My wording could be improved also. I would prefer the terms stronger or weaker acid or base rather than more acidic or basic. Remember, the Arrhenius definition is the simplest definition of acid base  good for beginners, but pH is very complex. As you go on to the Brønsted-Lowry or Lewis acid theory these are the terms used. I do not know of any hydro sites involving the Brønsted-Lowry or Lewis acid theory in their discussion of hydro reactions, but it might be interesting to see them.

I suppose an explanation of the use of a common logarithm (base 10) is unnecessary for the discussion of Ph for the layman, but it is the mathematical explanation for the factor of 10. My background is science and engineering chemistry, which makes me focus on the math of reactions. Therefore, whenever I see a logarithm I automatically look at the base. Althought this is unnecessary for your topic, I personally believe it would be nice to see advanced material on the pH for hydro growers.

    Bookmark   April 2, 2006 at 7:38AM
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Dear Baci,

You would make a good politician as they use similar limp excuses on this side of the Pacific ... being "quoted out of context", or "misconstrued", or something similar to counter being caught out.

Oh, by the way, I have found another error on you FAQ page, right near the bottom where you claim that Calcium Oxide, CaO is insoluble. Calcium Oxide, or Quicklime, or Dead burnt limestone does in fact react explosively with water and hydrolyses to Calcium hydroxide, otherwise known as Hydrated Lime, or Builder's Lime. Bricklayers mix Hydrated Lime with one part of Portland Cement and up to six parts of Bricklayer's sand to make mortar for bricklaying.

While you are at it, please fix this reference to CaO as well as fixing up "Phosphorus" and rectifying:

"A solution at pH = 5 is ten times less acidic than one at pH = 6" ... which is NOT CORRECT.

It should be modified to read:

"A solution at pH = 5 is ten times MORE acidic than one at pH = 6".

Hydroponic growers do not need to know anything about logarithms, nor do they need highly technical explanations on how things work ... it just turns them off.
All that they need are simple explanations ... "if you cannot dazzle them with science, just baffle them with bull" .... does not work over here and it should not work over there either.

I might re-write this topic, clarifying some of the points.
In the meanwhile, please fix your FAQ page.


    Bookmark   April 3, 2006 at 6:29AM
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Baci is one of the most knowledgeable contributors to this forum that I've come across. I respect his input and balanced advice. I myself find it annoying to see this forum continuously used as an advertisement site for people's websites. Let's get back to making this forum stimulating, interesting, and fun!

    Bookmark   April 4, 2006 at 3:47AM
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Forum users come to the forum to learn. Although disagreement can serve to clarify material, when civility is lost, it is an impediment to learning and does not benefit the forum.
The FAQ is intended to be written by the forum users. Therefore, for the benefit of the forum, I will replace the pH FAQ with your post above, since you feel it more accurately reflects the needs and level of the forum. It should thus be material which you agree with.
Please allow time to do this as sometimes the link does not come up. If I can not fix it in the next couple of weeks I will re-post.
The iVillage acquisition has resulted in a rearrangement in which they did not know who would fix the FAQ link. The NBC acquisition probably further compounds things. In other words, it is supposed to come.
I also find it annoying to constantly see the forum used as an advertisement for personal web sites &/or companies. It takes away from the content, & lately it has looked as a forum of advertising and promotion without content. I never minded the paid ads, but it is depressing to constantly see the free "plugs" when I come here. There is some concern as to whether the web sites linked to will be copyrighted material of the GW owner & will be used for future publication. There are posts on the suggestions forum & other forums concerning this topic.
Thanks, Hank, for your comments. Your posts have consistently reflected nothing but unselfish and substantive contribution to the forum.

    Bookmark   April 4, 2006 at 7:40AM
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This thread reminds me of the movie, "Annie Hall" starring Woody Allen.

In the movie he defends basketball by saying, "What's fascinating is that it's physical. You know, it's one thing about intellectuals, they prove that you can be absolutely brilliant and have no idea what's going on. But on the other hand ... the body doesn't lie."

I'm sorry but Baci is an intellectual who has no idea what's going on.

    Bookmark   March 9, 2010 at 12:36PM
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*chuckles* good lawd!

Jim, thanks for the clarification...that was an extreme help and it made perfect sense. I SO appreciate you taking the time to post that for us newbies!


    Bookmark   March 9, 2010 at 1:48PM
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