A water sample was analyzed and was found to have the following constituents (sa

Question

A water sample was analyzed and was found to have the following constituents (same analysis as for part of the homework) Ca2, mg/L 123 Mg2, mg/L 12 Na", mg/L 22.1 K', mg/L 3.8 Fe, /L 5.8 Mn2, mg/L 1.5 HCO, mg/L 82 SO,2. mg/L 122 CI, mg/L 112 CO,2, mg/L 6.0 I emperature 25°C 1. Calculate the alkalinity (exactly). 2. Calculate the total, carbonate, and non-carbonate hardness of the water include contributions made by iron and manganese). How many mL of 0.02N H,SO, would be required to neutralize the bicarbonate alkalinity in a 50 mL sample? 4. Draw a bar chart for the water (see pages 287-288 for an example). 5. Based on the solubility product for calcium carbonate, how much calcium (mg/L as CaCO,) should be soluble in this water? Is the water under-saturated or over-saturated with respect to calcium? 6. Based on the solubility product for magnesium hydroxide, how much magnesium (mg/L as CaCO,) should be soluble in this water? Is the water under-saturated or over-saturated with respect to magnesium?

Explanation / Answer

1. Alkanityof water sample is due to the prsesnce of OH-(hydroxide ions), HCO3- (bicarbonate ions) and CO32- (carbonate ions) or the mixture of two. Hydroxide ions and bicarbonate ions cannot exist togather as they will react to form corbonate ions and water.

Therefore, in the given sample of water total alkalinity = conc. of HCO3- + conc. of CO32- = 82mg/L + 6.0mg/L = 88 mg/L

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