During a titration with EDTA, using eriochrome black T as indicator to determine Ca
2+
, an
analyst obtained the following volumes of EDTA in three different trials: 5.01, 4.93 and 4.98
mL. What is the Ca
2+
concentration (mol/L) in this sample if the concentration of the EDTA
standard used was 0.035 mol/L, and the volume of sample titrated was 20.00 mL?
2) Considering the same type of experiment described in the previous question, calculate the
Ca
2+
concentration in a sample which consumes 20.05, 19.96 and 20.03 mL of a 0.0084 mol/L
EDTA solution in three different trials. In this case, the sample volume used was 15.00 mL.
3) What is the CaCO3 mass percentage in a seashell sample presenting 0.0158 g of this
compound for an initial sample mass of 0.0165 g?
Do not forget to report the correct number of significant figures. You may also want to use
the following equation in exercises 1 and 2: n = M x V, where n is the number of mols, M is
the molarity in mol/L, and V is the volume in L.