Methods of measuring pH
To measure the
pH of a solution, a digital pH meter, or pH papers such as litmus
are used.
These methods can be expensive, especially if you are buying
the pool test strips.
pH meters begin selling for $70 and usually run
$120 if you can even find one.
Red Cabbage is happening
You really
don't have to use either of them, as nature provides us with pH indicators in
the form of plant pigments which change color over different pH ranges. One of
the very best is red cabbage. Red cabbage juice will function over a wide pH
range, from as low as pH 1 up to pH 13.
Preparation
There are
many ways to prepare the indicators,
My favorite is to chop up 1/2 of a head
of red cabbage
place it in a pot of water, then
bringing it to a boil,
let it cool down slowly the color slowly drains out of the cells.
Filter
and discard the solids,
evaporate and concentrate the juice
Don't over heat it too much, it will get brownish if you do.
Then dip
blotter paper or paper towels , in the juice. Spread them out to dry, then
dip them again so they get a double dose
If you wish you may iron them flat,
run through a shredder for individual strips.
I usually just put drops on a
full sheet.
pH measurements What to
measure
Measurements are taken on polar (water soluble)
solutions only.
Taking a pH reading on a non-polar (oil soluble) solution is futile.
If you do get a pH reading you are actually measuring the pH of any
polar solvent residue trapped in with the non-polar.
this may be an
indication of purity of the non-polar and not much else
Above are pictures of the actual, indicator in water at the various pH's, Below is a color bar.
Do you see a problem in determining various pH from the top photo?
Many of the water colors look the same
pH 3
thru pH 6
pH 7 thru pH 9
pH 11
and pH12
The timing of the color indicator is not included.
Most indicators
have a certain time window in which they should be read, this true with
red cabbage also
The pH is read within 3 -10 seconds and compared to
the lower color bar.
examples
pH-11
A drop of a solution at pH 11 will
change from purple to yellow-green very fast (3-10 seconds), and
slowly continue changing until it is yellow. If you check the paper after
30 seconds, you would not know if the pH was 11 or 12 since both would be yellow
pH12
At pH of 12+ the drop will turn the paper from
purple to green to yellow very fast (3-10 seconds)
pH7.2
At the very first sign of blue
within a few seconds of placing the drop, stop, no more acid is needed,.
As
you are shooting for the correct neutral pH you will be adding acid and bringing
it down from pH 12+.
so the tests will appear yellow then green then one
test will be blue after 3 seconds
Accuracy vs Precision
Accuracy -
is closeness to the actual true value
Precision - is internal
closeness of a set of measurements
Using the paper is too kewl, because before long you won't care
what the pH is.
All that will matter is that you saw the color change from
purple to green to yellow immediately after putting a drop on the paper.
At
the neutral end you first saw a bit of blueness so you knew you were at
the neutral pH spot.
It is so perfect, I marvel still at all the go-go, that
was dreamt up with this red cabbage paper.
The pH paper is accurate to at
least 0.4 of a pH unit or even better when you include the time
factor.
After doing it a few times your precision will be excellent 0.1 -
0.2 pH unit
The pH meters are accurate to 0.2 pH units
One
pH reading
Have developed a way to almost avoid
taking a pH reading at all.
You may only need to take one reading, to
verify the upper point has been reached
I suggest you save this method for
the day when you have had several successful reactions. The observations you
need to make will be clear after you have already seen them several times.
The alkaline reading
After the completion of the reaction,
add 200 ml - 400 ml of water, then boil for 5 minutes. This should result
in a clear fluid with the RP settling to the bottom( a few aluminum potpies from
soft drink cans, helps remove any excess iodine, when boiling).
Filter the
RP out of the reaction mix, ,
Begin adding base or a Sodium hydroxide
solution.
Observation is the key, just watch what happens.
First the
solution turns white when the lye hits it, then it clears ,
With more
additions of lye the water layer becomes milky white, and stays milky
white for more than 30 seconds, you are very close to the alkaline pH level.
The milky white is what?? A white precipitate?? It can only be that which you
are looking for.
Chili in the free base form, loosing its water solubility,
coming out of the water layer
Mix it well and observe closely for the whiteness to go away a little bit,
leaving the water layer cloudy
Add another dose NaOH, this puts
it over the line, right where it needs to be
add your non-polar solvent.
You can be certain because
1. the chili was seen becoming non polar.
2. additions of NaOH do not form any added white precipitate in the water
layer.
3. you may see a "lye lock", solidifying the water layer.
Wait a few minutes then test the pH of the water layer just to be certain it
is over pH 12.4
Toss in some table salt if you wish.
Lye Lock
Watch out for a solidification of the lye/water
layer (lye lock) too much solid material in the water lye , as it cools from the
heat released by adding the NaOH, the NaOH begins to solidify. One good thing is
you know the pH was high enough.
probably close to pH 13.7
Dilute it
with warm water before it hardens, and begin draining out the lower layer,
contine diluting, or it will harden then it is more difficult to keep dilute
keep it separated (don't shake)
Remove the lye solution
Washing the chili
After removing the lower water layer
Wash the non-polar/meth with about 1/2 volume of d-water
This means add water, shake fairly well, let it layer, and fully separate
and remove the water layer
Repeat the d-water wash three (3) times
Adding the HCl
Add an 1/2 volume of d-water
again
Toss in a couple healthy squirts of HCl.
A bit less HCl than
is needed, that will be 1 ml of 30% HCl for each gram of
expected product
Shake well
allow to form into two layers
Separate
and save the water layer in your boiling bowl
Evaporate the
water away
Enjoy the great crystal chili that pops out
then do another pull
Add more d-water to the non-polar/meth
Couple more squirts of HCl
shake well,
allow to layer
separate and evaporate
Continue in this fashion
Eventually you will get to the last pull,
you will know it is the final pull because a great deal of nasty HCl
vapor will come off when evaporating the mixture ,
You will have to
wash the excess HCl out of the crushed crystals, of this final pull,
with acetone.
All the pulls are the same and great chili even though the pH was at 10 , 9,
8 or 7 when the shit was dropped out of the non-polar.
WHY?
Most of it
happened with in a small pH range of pH 10.0 to pH 8.5 As the chili takes
on a H+ attached to its nitrogen, it is capable of
hydrogen bonding . Once it accepts a Cl- ion, it becomes
suddenly very water soluble.
It is related only partially to the pH
because if you were very careful about any ions you could concievably maintain
the freebase at pH 7.0 but the -OH would interfere .
In this case it
is the Cl- that is the primary factor affecting formation of the water soluble
salt. That is why it is very important once you have the freebase form, to only
use very pure distilled and deionized water to wash the freebase clean. because
any negative ion , is going to cause a loss of product when washing the free
base, depending upon the pH and a dozen different concentrations of whatever
ions are present,
The pH will drop with each washing. The pH of pure water is 7.0, distilled is often 6.8 , tap water can be up to 8.5+
The less foreign ions present the better control you will have.
Better
yields
Better dope
Considering the shitty quality of muriatic acid, it
would be great to distill your own.
If you are consistantly getting dope
that smokes burns dark and gakky , consider the source of your HCl probably also
contains sulfuric acid, and you might consider gassing it onstead or
distill your HCl first.