Question

Shown below are the results of water quality analyses of a groundwater source. Because all of the constituents were not analyzed, an ion balance may not be achieved. The pH of the water is 7.6.

a. (8 points) Prepare a bar chart of water composition.

b. (6 points) Based on the bar chart, determine the total hardness, carbonate hardness, non-carbonate hardness, and alkalinity (in the unit of mg/L as CaCO₃).

c. (6 points) Estimate the concentrations of carbonate (CO₃^2-) in the water. Express your answer in mmol/L. Given that pK_a1 and pK_a2 of H₂CO₃ are 6.35 and 10.33, respectively.

d. (6 points) Dolomite (CaMg(CO₃)_2(s)) is found in the aquifer sediment where the water sample was collected. Based on the water composition, is dolomite dissolving or precipitating? Given that the Ksp of CaMg(CO₃)_2(s) is 10^-17.09.

Constituent	Concentration (mg/L as the ion)
calcium (Ca2+)	150.3
magnesium (Mg2+)	14.6
total iron (Fe3+)	1.2
sodium (Na+)	100.0
bicarbonate (HCO3-)	450.0
chloride (Cl-)	201.4

Answer 1

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