WM Session
10: Putting it all together.
Step 1: Tabulate the data to list the concentrations in ppm and mM
for all the cations and anions analyzed in lab on each water sample. For example:
|
Source |
Hy-Vee Spring |
|
|
|
Ion |
Concentration, mM |
FW g/mole |
Concentration, ppm |
|
Na+ |
0.030 |
23 |
7.0 |
|
Ca2+ |
2.2 |
40 |
88 |
|
Mg2+ |
0.091 |
24 |
2.2 |
|
HCO3- |
4.0 |
61 |
246 |
|
Cl- |
0.26 |
35.5 |
9.3 |
|
F- |
0.0058 |
19 |
0.11 |
|
NO3- |
0.00045 |
62 |
0.028 |
|
{(SO4)2-} |
0.173 |
96 |
16.6 |
|
pH |
8.0 |
|
|
|
|
|
TDS expt: 380 |
TDS calc: 369 |
|
Total anions |
4.266 (-SO4-2) |
|
|
|
Total cations |
4.612 |
|
|
Step 2 Calculate the total
millimolar concentration of cationic charges and of anionic charges for the
data in each sample. Are they
equal? If not, which one is larger? Sulfate anion may be present in drinking
water. Calculate the millimolar
concentration of sulfate required by the conservation of charge condition, SCcZc = SCaZa.
Cations: 0.03 +
2(2.2) + 2(0.091) = 4.612 mM
Anions: 4.0 + 0.26
+ 0.0058 + 0.00045 = 4.266
Sulfate = (4.612
– 4.266)/2 = .173 mM
Note: Think about how many significant figures you
can report for your data.
Step 3. Calculate the
concentration of total dissolved solids (TDS) in ppm from your. How does this compare to your conductivity
measurements? Why might there be
differences?
The sum of the
concentrations in ppm is 369 ppm vs 380 ppm
Step 4. Propose a mixture
of specific salts which would yield a given composite analysis.
What are the
principle salts and what does this tell you about the source of the water?
end