Questions go togheter. Some water utilities use ferric chloride, FeCl 3 , as a c
ID: 802551 • Letter: Q
Question
Questions go togheter.
Some water utilities use ferric chloride, FeCl3, as a chemical coagulant. It reacts with water to form ferric hydroxide, Fe(OH)3, according to the following balanced equation: FeCl3 + 3HCO3- ---> Fe(OH)3(s) + 3Cl- + 3CO2
A) will the pH increase or decrease when the ferric chloride is added? explain
B) How many mg/L of bicarbonate will be consumed by the addition of 25 mg/L of ferric chloride?
C) Fe(OH)3 is better known as "rust". Consumers might be concerned about rust being added to their water; and other, having heard that iron causes water to taste bad or stain porcelain, might wonder why iron was being intentionally added. Assuming that the pH of the treated water is 6.5, and that the solubility of Fe+3 is governed by the solubility of Fe(OH)3, how much dissolved Fe+3 is expected to remain in solution? Use a pKs value of 38.0 for the freshly precipitated Fe(OH)3(s)
Explanation / Answer
Answer: A
The hydroxyl ions increases the pH values of solution, therefore as by adding the FeCl3 will also increase the Fe(OH)3, as a result pH will increase.
Answer : B
According to the given equation, 1 mole of FeCl3 consumed 3 mole of bicarbonate.
1 mole of FeCl3 = 16220.7 mg
3 mole of bicarbonate= 150334.60 mg
Therefore, 1 mg/l of FeCl3= 9.26 mg/l of bicarbonate
So, 25 mg/L will consume = 231.5 mg/L
Answer c:
As the pH will low from 6.5, the solution will keep contain the minerals or ions in it. Here as the pH of water is 6.5, therefore, the iron content will be completely consumed in the solution.
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