pH,
AND ALL THAT! (Conclusion)
Ron
Knowles.
Q.
That seems to be born out by just lunch I made up the developers and the
buffers. Made one buffer from deionised water, which I got from Halfords
and made the other buffer up from ‘purified’ water from Boots, both of
which I think are deionised. Boots say theirs is distilled but I don’t
be1ieve it, and in both cases there was a difference, initially, before I
put the chemical in when I put the Borax in the one to give the lower
buffer, to give a pH of 9.2. I put the Borax in and it registered
9.2. I had previously set the pointer to 9.2 and it came
back to 9.2 exactly. And
then the other one, the buffer for 11.72, the needle swung over so it
indicated to me that any variation in the pH of the water, initially made
no difference to the settlement figure.
A. It shouldn’t. In fact the only thing that could
cause trouble would be reflected in the CONDUCTIVITY of the water.
That is the extent to which it would take an electric current. Pure water
isn’t quite an insulator but very nearly it is. As soon as you put
saline impurities — a trace of sa1t--water or something like that it
will conduct electricity like new. But if the water is good acid free from
electrolite impurities you should find it to have a very high resistance -
electrical resistance. You
put.two probes from-your meter into distilled water it ought
to show almost open circuit.
Q.
Really? As much as that?
A. Yes.
Q. Fkirther on the micro-ammeter?
A. It ought to show virtually nothing. But if
you put a wee spot of your buffer
or a wee spot of acid in there.
Q. It will swing over?
A. Yes it will swing over.
Q. So, in actual fact what you are saying
is what we
in the Club have
all been doing and that is ignoring the pH of the distilled water
initially and just putting our chemicals in to make up the buffer and
that, you say, gives a reliable figure - providing the amount of chemicals
is correct and is pure and so on?
A. I would think that would always work. As I say they are only tests you
want. The only time you may be worried slightly is if you are using very
dilute buffer solutions, and the pH of the water was smaller than the 6 or
higher than 8 or 9.1 If the water was that far wrong you would have
grave suspicions.
Q. Well I’ve, rarely found the water to be. I
think the water I’ve used this time to be .6.2 -
6.3.
A. That would be normal because the deionised water is still containing
same carbon dioxide and that is acidic and will bring the pH down towards
6 beIow if you took some of that water and boiled it you would boil most
of the carbon dioxide out and the pH ‘ought to be near to 7.
Q. And, of course, one of the things we have to be careful about is
that when we make up a buffer, leaving it around too long it can
easily take up some carbon dioxide?
A. It will certainly take up some carbon dioxide...and go on doing it if
it a Borax buffer.
Q. Yes, well that’s what I use and when
I make up my buffer I do my tests more or
less straight away before it has a chance to, for. when. I’ve had
it standing by and then done the test again, and done the re~registeration
of the machine, it’s always going back a point or two.
.A. Well..no, I think there is something curious there....
Q Well, it might have taken a little bit of carry-over, shall we say, in.
the water from the cleaning of probes.
A. Yes The amount of carbon dioxide it would take up is
comparitively small but slow but inevitably if left open in the same
sense.
Q. Blowing through a straw
into it...that would: do quite a lot, wouldn’t it?
.A. Yes, If you left an ordinary solution open some of the water would
slowley evaporate -well it’s rather a stagnent condition in an un—stoppered
bottle and so,. it’s going to take some time for things to happen - it s
going to be slow.
Q, Well, I think you’ve answered the points of my colleagues in the Club
wanted to know, but I wanted officia1 confirmation of what I thought was
the situation and now you’ve given it. Thank you very much.
So there are the views of three eminent chemical bods and the
information should be of immense value to the members of the C.R.C who
Weigh &mix. I must confess their findings are much less complicated
than I have always feared and, the formerly mysteries of pH values much
more clear.
Quite obviously, from the information given,
it now becomes understandable why the commercial processing kits fail to
specify what water to use
when diluting their near saturated solutions. Providing they get the pH
right it will STAY right when made up to working strength.
I must. say I am VERY surprised to be tolled
that PURE water, though not quite and electricity insulator, VERY NEARLY
IT IS. Bet that comes as a surprise-surprise, to very nearly everyone of
you. But that’s what the man said.
Without labouring the point of pH and water
too much more I must mention that there is a filtration jug available from
health stores which using ordinary tap-water poured in at the top, comes
out with most of the impurities gone and I have measured the out going
liquid at pH 6.6. Quite near enough to give a suitable base for buffer
chemicals to be added to bring the reading to either our usual 9.2 or
11.72. But I don’t advise it to be used for ordinary drinking water
purposes as the more alkaline water is preferable from a health point of
view, Or so we are assured.