Let's break down the problem step by step.
1. To find the volume of EDTA used in titrating Ca2+ in the hard water, first determine how much EDTA was used to titrate both Ca2+ and Mg2+:
Volumes of EDTA:
- Total EDTA used for both Ca2+ and Mg2+ = 22.44 mL
- EDTA used for Mg2+ (from Part 2) = 10.11 mL
So, the volume of EDTA used for Ca2+ would be the total volume minus the volume used for Mg2+:
Volume of EDTA for Ca2+ = 22.44 mL - 10.11 mL = 12.33 mL
2. To find the moles of EDTA in the volume used for titrating Ca2+, use the concentration of the EDTA solution from Part 2 (0.00484 M):
Moles of EDTA = (12.33 mL)(0.00484 mol/L) * (1L/1000mL) = 0.000059676 mol (rounded to 3 decimal places)
3. In EDTA titration, the molar ratio between EDTA and Ca2+ is 1:1. So, the moles of Ca2+ in the 100.0 mL volume of water are the same as the moles of EDTA used:
Moles of Ca2+ = 0.000059676 mol
4. If the Ca2+ comes from CaCO3, then the moles of CaCO3 in the water are the same as the moles of Ca2+:
Moles of CaCO3 = 0.000059676 mol (in 100 mL of water)
To find moles of CaCO3 in one liter (1000 mL) of water, multiply by a factor of 10:
Moles of CaCO3 in 1 L of water = 0.000059676 mol * 10 = 0.00059676 mol
5. To find the grams of CaCO3 per liter, use the molar mass of CaCO3 (100.09 g/mol):
Grams of CaCO3/L = (0.00059676 mol)(100.09 g/mol) = 0.059681 g/L
6. Recall that 1 ppm CaCO3 is equal to 1 mg of CaCO3 per liter. To convert grams to milligrams, multiply by 1000:
Water hardness in ppm CaCO3 = 0.059681 g/L * 1000 = 59.681 ppm (rounded to 2 decimal places)
So, the water hardness is approximately 59.68 ppm CaCO3.
A 100.0 mL sample of hard water is titrated with the EDTA solution from Part 2. The same amount of Mg2+ is added as previously, and the volume of EDTA required is 22.44 mL
What volume of EDTA is used in titrating the Ca2+ in the hard water?
How many moles of EDTA are there in that volume?
How many moles of Ca2+ are there in the 100.0 mL volume of water?
If the Ca2+ comes from CaCO3, how many moles of CaCO3 are there in one liter of the water?
How many grams of CaCO3 per liter?
If 1 ppm (part-per-million) CaCO3 = 1 mg per liter, what is the water hardness in ppm CaCO3?
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