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?
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.
To answer these questions, we need to understand the concepts of titration, moles, and calculation of concentrations.
1. Volume of EDTA used for titrating Ca2+:
Since the same amount of Mg2+ was used as before (Part 2) and 22.44 mL of EDTA was required, it means that this volume of EDTA was used to titrate both Mg2+ and Ca2+. Therefore, the volume of EDTA used for titrating Ca2+ is also 22.44 mL.
2. Moles of EDTA in the volume used:
To calculate the number of moles of EDTA, we need to know the molar concentration of the EDTA solution used. With that information, we can multiply the volume used (22.44 mL) by the molar concentration of EDTA to get the moles of EDTA.
3. Moles of Ca2+ in the 100.0 mL volume of water:
To calculate the moles of Ca2+, we need to know the molar ratio of EDTA to Ca2+ in the reaction. From the question, it is implied that the same amount of Mg2+ as before was used. So, assuming that the molar ratio of EDTA to Ca2+ and EDTA to Mg2+ is 1:1, we can say that the moles of Ca2+ in the 100.0 mL volume of water is the same as the moles of Mg2+ in Part 2.
4. Moles of CaCO3 in one liter of the water:
From the molar ratio of Ca2+ to CaCO3, we know that the molar ratio is 1:1. So, the moles of CaCO3 in one liter of the water is the same as the moles of Ca2+.
5. Grams of CaCO3 per liter of water:
To calculate the grams of CaCO3 per liter, we need to know the molar mass of CaCO3. With the moles of CaCO3 and its molar mass, we can calculate the grams per liter.
6. Water hardness in ppm CaCO3:
To calculate the water hardness in ppm CaCO3, we need to know the mass of CaCO3 and the volume of water. In this case, since it is given that 1 ppm CaCO3 is equal to 1 mg per liter, the water hardness in ppm CaCO3 is the same as the mass of CaCO3 in mg per liter of water.
To calculate the specific values, you would need to provide additional information such as the molar concentration of EDTA solution and the molar mass of CaCO3.
To find the volume of EDTA used in titrating the Ca2+ in the hard water, subtract the volume of EDTA used in Part 2 (22.44 mL) from the total volume of EDTA used (100 mL). Therefore, the volume of EDTA used in titrating the Ca2+ is 100 mL - 22.44 mL = 77.56 mL.
To find the number of moles of EDTA in that volume, we need to know the concentration of the EDTA solution. Let's assume the concentration is C mol/L. Then, the number of moles of EDTA is calculated using the formula:
moles of EDTA = concentration (mol/L) * volume (L)
Given that the volume of EDTA used is 77.56 mL = 0.07756 L (converted from mL to L), we can calculate the moles of EDTA using the above formula.
moles of EDTA = C (mol/L) * 0.07756 L
The number of moles of Ca2+ in the 100.0 mL volume of water can be determined using the stoichiometry of the reaction. Assuming the same amount of Mg2+ is added as previously, we can use the ratio of moles of EDTA to moles of Ca2+ from the previous part. If the ratio of moles of EDTA to moles of Ca2+ is R, then:
moles of Ca2+ = moles of EDTA * R
To find the number of moles of CaCO3 in one liter of the water, we need to use the stoichiometry of the reaction and the molar mass of CaCO3. Assuming the reaction is:
CaCO3 + 2H+ -> Ca2+ + CO2 + H2O
We can see that one mole of CaCO3 produces one mole of Ca2+. Therefore, the number of moles of CaCO3 is equal to the number of moles of Ca2+.
To find the grams of CaCO3 per liter, we can use the molar mass of CaCO3, which is 100.09 g/mol.
grams of CaCO3 per liter = moles of CaCO3 * molar mass of CaCO3
To determine the water hardness in ppm CaCO3, we can use the fact that 1 ppm CaCO3 = 1 mg/L. Therefore, the water hardness in ppm CaCO3 is equal to the grams of CaCO3 per liter.
water hardness in ppm CaCO3 = grams of CaCO3 per liter