Homework Set #1

1. Measures of Concentration & Charge Balance

Northampton MA has recently completed construction of a filtration plant to treat their surface water supplies. This is located near one of Northampton’s two major surface water sources, the Mountain Street Reservoir in Williamsburg. This source is characterized as low-alkalinity and low-hardness, quite typical of most surface waters in New England. On March 19, 1997, a sample of the Mountain Street Reservoir water was collected and submitted for chemical analysis. The results are shown below.

Constituent	Concentration	Units
Turbidity	0.59	NTU
TDS	29	mg/L
Color	10	Color units
Odor	1	TON
pH	6.75	Log units
Total Alkalinity	13	mg-CaCO₃/L
Total Hardness	20	mg-CaCO₃/L
Calcium	6.7	mg/L
Magnesium	0.89	mg/L
Aluminum	<0.05	mg/L
Potassium	<1	mg/L
Sodium	5.0	mg/L
Iron	<0.05	mg/L
Manganese	0.016	mg/L
Sulfate	5.9	mg/L
Chloride	3.0	mg/L
Silver	<0.005	mg/L
Copper	<0.01	mg/L
Zinc	<0.05	mg/L
TOC[1]	3	mg/L

a. Estimate the bicarbonate concentration assuming that all of the measured alkalinity is bicarbonate.

b. Calculate the ionic strength

c. Determine the “analytical” concentration of [H⁺] using the Debye-Huckel equation.

d. Perform a charge balance on this water based on the measured concentrations. Is there apparent excess charge, and if so, why?

e. Calculate the “theoretical” TDS based on the chemical analysis above and compare with the actual measured TDS. Are they different and if so why do you think this is the case?

2. Activity

A series of 10^-3 F HCl solutions are prepared[2], each solution containing a different concentration of KCl in the range of 0.01 F to 0.50 F. Plot pH (i.e., -log{H }) vs log I using:

	a. Davies Equation;
	b. Extended Debye-Huckel Equation.

Assigned: 14 Sept 11

Due: 21 Sept 11

[1] Not measured; estimated from historical data

[2] F refers to Formality, which is the concentration in moles per liter that would exist if the material added to the solvent did not dissociate or react in any way to change its chemical structure

CEE 680