If 75mL of a hard water sample required 23.00 mL of .200 M EDTA, calculate the total hardness
To calculate the total hardness of the water sample, we need to determine the concentration of calcium and magnesium ions present in the water.
Step 1: Find the moles of EDTA used.
We know that the volume of the EDTA used is 23.00 mL and the concentration of EDTA is 0.200 M.
Using the formula:
moles of EDTA = volume (L) x concentration (mol/L),
we can convert the volume to liters:
23.00 mL = 23.00 mL / 1000 mL/L = 0.02300 L.
Now we can calculate the moles of EDTA used:
moles of EDTA = 0.02300 L x 0.200 mol/L = 0.00460 moles.
Step 2: Determine the moles of calcium and magnesium ions.
Every mole of EDTA reacts with one mole of calcium or magnesium ion. Since the stoichiometric ratio is 1:1, the moles of calcium and magnesium ions in the water sample will be the same as the moles of EDTA used.
Therefore, the moles of calcium and magnesium ions is 0.00460 moles.
Step 3: Calculate the total hardness.
The total hardness is usually expressed in terms of milligrams per liter of calcium carbonate (CaCO3). Each mole of calcium or magnesium ion is equivalent to the molecular weight of CaCO3 (100.1 g/mol).
Therefore, the total hardness can be calculated using the formula:
total hardness (mg/L) = moles of calcium and magnesium ions x molecular weight of CaCO3 (mg/mol).
total hardness = 0.00460 moles x 100.1 mg/mol.
Calculating the total hardness:
total hardness = 0.460 mg/L.
So, the total hardness of the water sample is 0.460 mg/L.