What are the ions causing water hardness and what does it mean if a report show
ID: 1004958 • Letter: W
Question
What are the ions causing water hardness and what does it mean if a report show s that water hardness of a sample is 100 ppm? A solution of CaCO_3 was prepared by dissolving 0.008 g of CaCO_3 (MM 100.0 g/mol) in 100 mL 1 M HCl. Calculate concentration of the CaCO_3 in the solution in: Molarity PPM (part per million) 200 mL of a sample of water was titrated with 100 mL 0.022 M EDTA in the presence of an indicator. Assume the water density is 1.0 g/mL Calculate volume of EDTA required for one liter of water. Calculate water hardness of the water sample. Why do we need to adjust the pH of the solution to pH 10 before titration with EDTA?Explanation / Answer
1.
The presence of ions like Mg2+ and Ca2+ renders water hardness. EDTA diesnot make water hard, but is used in calculating the hardness of water.
100 ppm of hardness means 100 g of Ca2+ or Mg2+ or both are present in 1 million g of water.
2.
100 ml 1 M HCl
no. of moles CaCO3= 0.008/100= 0.00008 moles
concentration= (8*10^-5/100)*1000= 8*10^-4 M
3.
a)
200 ml of water is titrated using 100 ml of water.
so 1000 ml of water would be titrated using 1000/2= 500 ml of EDTA
b)
moles od EDTA used= 0.022*0.1= 0.0022 moles
therefore moles of Ca2+/Mg2+= 0.0022 moles
because the reaction is as follows:
H2Y2- + M2+ MY2- + 2H+
where M=Ca2+/Mg2+
Y= edta
generally water samplw contains CaCO3 as hardness.
so mass of Ca2+ present= 0.0022*100g/mol= 0.22 g
0.22 g in 200 g of water.
0.11 g in 100 g of water.
4.
At this pH, the amount of Y4- is higest for binding to M2+. Also it is the optimum pH for stability of the edta and M2+ complex.
Related Questions
drjack9650@gmail.com
Navigate
Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.