Change in the alkalinity protocol
for GLOBE manual, phase III

Dear Students,

We have a change to announce to the section of the GLOBE manual which deals with preparing the alkalinity standard. In the interest of ensuring the highest caliber of reliable data, we have re-written things to be a little clearer, and reliable. Please make note of these changes and include them in your manual for future use.

The Problem with the previous method

The 0.05 g. scoop in the alkalinity test kit is inaccurate for our purposes. It is designed to deliver 0.05 g. of the indicator powders which do not need to be perfectly accurate in terms of the amount used. When this scoop is used to deliver baking soda (NaHCO3) it delivers a smaller mass. We recognized this early in designing the standard protocols, and planned accordingly. However it now turns out that the scoops are not consistant enough for use in creating the alkalinity standards

The Solution to the Problem!

We have decided to change the GLOBE manual to make the alkalinity standard more consistant.

Equipment required:
 1)        500 mL beaker
 2)        500 mL grad cylinder
 3)        50 mL grad cylinder
 4) 	   stirring rod
 5)        distilled water
 6)        ability to weigh out 1.9 +/- 0.1 g
 7)        Over-the-counter Baking Soda

Procedure:

Please mark changes in your GLOBE manual on page 3-33. Note: We are changing the procedure for the preparation of the alkalinity standard, not the procedure for the overall measurement of alkalinity at the hydrology site.

Text to be deleted:

Beginning at page 3-33 Baking Soda Standard and continuing to, but not including: Quality Control Procedure on the same page.

Text to be added:

Beginning at page 3-33

Baking Soda Standard
 
1)  Using your balance, weigh out 1.9 g. baking soda and add it to
    your 500 mL graduated cylinder.  Make sure to transfer all of the
    baking soda to the cylinder.

2)  Fill the 500 mL graduated cylinder to the 500 mL mark with Distilled Water.

3)  Pour this solution into the 500 mL beaker, and stir it with a stirring
    rod to make sure all of the baking soda has dissolved.

4)  Pour 15 mL from the beaker into the 50 mL graduated cylinder.

5)  Pour the 15 mL of your baking soda solution into the 500 mL graduated 
    cylinder.

6)  Fill the 500 mL graduated cylinder to the 500 mL mark with Distilled Water.
 
7)  The solution in your 500 mL graduated cylinder is your standard.


The true alkalinity of this baking soda standard is 68 mg/L as CaCO3 and 
should require 10 drops +/- 1 drop to reach color change.  The true value for 
distilled water is usually below 14 mg/L. 

Sincerely,

Roger Bales
Professor of Hydrology & Water Resources
University of Arizona