Re: making samples to test for pH and Alkalinity

The presence of alkalinity in a water sample may be due to many different 
substances.  However, for the sake of simplicity, the presence of 
bicarbonate, carbonate, and hydroxide ions is commonly considered as 
alkalinity.  The points of change in color of phenolphthalein and methyl 
orange indicators, which occur at pH 8.3 and pH 4.3, provide standard 
reference points which are almost universallly used to express alkalinity.

From the form of your question, you realize that two samples of water with 
the same pH can have widely different alkalinity values.  The standard 
calculations for pH are simple for sodium hydroxide solutions, but get 
more difficult for buffer solutions such as carbonate/bicarbonate 
solutions.

The easiest way to make the kind of solutions you requested is to add 
dilute sodium hydroxide solution to distilled water while measuring the pH 
on a pH meter.  This "titration" can give you a solution of pH 8.5 to 12 
with very little chemical.  A pH 10 NaOH solution has 10^-10 moles per 
liter Hydronium (H+) ion, and 10^-4 moles per liter Hydroxide ion (OH-).  
This would take only 10^-4 X 40,000 mg/mole or 4 mg of NaOH per liter of 
solution.  More concentrated solutions of NaOH can be dangerous and in any 
case approprate laboratory safety equipment must be worn.

To make a pH 10 Sodium Carbonate solution would require more calculations, 
and more Na2CO3.  The emperical approach seems appropriate for this level 
of non-major chemistry laboratory, however.  Secure the desired volume of 
distilled water and slowly add the Na2CO3 soluiton, while stirring, with 
pH electrodes immersed.  Continue adding the carbonate solution until the 
pH reaches the value you achieved with the NaOH solution.  NOTE:  The 
carbonate will form some bicarbonate and the pH of this buffer will not 
rise much above 12 no matter how concentrated the solution.  For example, 
a 0.1 N Na2CO3 solution has a pH of 11.6.  This would requrie 
approximately 10.6 grams of sodium carbonate per liter of distilled water.

You should be able to get the procedure for titrating the alkalinity from 
any analytical chemistry text or laboratory manual.  You can contact me 
directly at LONBROUSE@AOL.COM if you have any further questions about this 
subject.

References:  BETZ Handbook of Industrial Water Conditioning 8th Edition, 
1980.

            CRC Handbook, Chemical Rubber Company, 65th Editon, 1985.