In article ,
Mark wrote:
On Jun 17, 12:33=A0pm, M Q wrote:
Don Young wrote:
"bent" wrote in message
...

Ok, anybody want to attempt to splain to me why there is both a "pH"
(6.2-8.4) and a "Total Alkalinity" (0-240 ppm) scale on a pool water
chemical test strip kit . I have been using the strips that have the 4
square foam pads on the ~1/4" x 4" plastic strip that you dip in the
water, wait and then compare the colours change on the pads to the
reference colours on the label of the strips' bottle. The strips have a
colour range for Total Bromine (0-20 ppm), Free Chlorine (0-10 ppm), pH,=

and Alkalinity. Granted, it is likely that the strips I currently have a=
re
technically past the expiration date, and I will get some new ones soon,=

but firstly just to compare the results of the test between the old stri=
ps
and new strips, so I cna finish them off. Any comments on how off they c=
an
get with age?

This is my problem - ngQ(uestion):

I was taut in skool that pH and alkalinity was the same scale. The numbe=
r
is determined from the definition regarding the hydronium ion
concentration, and math or something like that. The pH of neutral water =
is
about 7. That it, it is neither acidic nor base in its chemical characte=
r.
If the number is low, like 3, it is "acidic" and if its high, like 9, it=

is alkaline (base). But if it is acidic (low number on the pH scale), by=

definiton it CANNOT be alkaline at the same time, or vice versa: it cann=
ot
be alkaline and be acidic too.

So why are there two scales on these (pool) water test strips, which rea=
d
from low to high for both pH and Alkaline? There is a pH and a Alkaline
scale!? So according to the pool companies you can have a low pH and a l=
ow
alkaline pool at the same time, or high & high, or low & high, or high &=

low.

Because I go to the chemical cupboard for the right chemical to fix the
problem (assuming all other parameters are being considerately moderated=

too) and I find chemicals labelled "pH Up", "pH Down", "Alkalinity Up",
and "Alkalinity Down"! And I don't want to do anything, (a) because the
strips may be wrong (via expiration) or (b) the pool chemical companies
may be full of crud.

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It's been a long time but I seem to remember that Total Alkalinity was
something that built up over time as you kept adding chemicals to adjust=
the
PH one way or another. At that time I think Total Alkalinity was somethi=
ng
you wanted to stay as low as possible and when it got too high you had t=
o
drain some water and replace it with fresh water.

Of course, I could be all wet. ;)

Don Young

You more or less got it right:
pH is a measure of the hydrogen ion concentration (lower number is
=A0 more acid and more hydrogen ions).
Total Akalinity is a measure of the amount of acid you have to add
to lower the pH.

In very pure water, only a little bit of acid (or a little bit of some alk=
ali,
such as sodium carbonate) will cause dramatic changes in pH.

In water with years of pool chemical residues, it can take much more
pH adjustment chemicals to make much of a difference.
Such solutions might be described as highly buffered.- Hide quoted text -

- Show quoted text -

yes...

I look at it this way... if you have say 1 gallon of water and say 10
grams of acid and 10 grams of base, the pH is neutral and the total
alkaliinty is low...

but instead if you have 10 pounds of acid and 10 ponds of base, ( I
exagerate here) the pH is still balanced but the total alkalinity will
be high.

Interesting chemistry you're using there.
If you mix a base and an acid together until you get a neutral pH, you don't
have a high alkalinity or a high acidity. What you have is a salt solution.

A glass of hydrochloric would rather nasty to drink.
A glass of sodium hydroxide solution would also be rather nasty to drink.
Mix them together until you get a pH of 7 and what you'll have is simply
a glass of water with salt disolved in it. Not the tastiest thing in the world
to drink, but not nearly as bad as either of the original 2 ingredients.

And yes, mixing a base and an acid will always get you a salt. The type of
base or acid you use will determine what salt is produced. And not all salts
are as benign as good old sodium cloride, but they're still just a salt.