Question

Twenty five milliliters (measured with a volumetric pipet) of a calcium solution containing 1.27×10−3 moles is titrated with EDTA and requires 20.14 mL to reach the equivalence point. What is the molarity of the EDTA solution?

Answer 1

The molarity of the EDTA solution is 0.1579 M.

Step-by-step explanation:

To find the molarity of the EDTA solution, we first need to calculate the number of moles of calcium in the solution using the given volume and moles. The number of moles can be calculated using the formula:

Moles = Volume (in liters) * Molarity

Plugging in the values, we get:

Moles of calcium = 0.025 L * 1.27×10⁻₂ mol/L = 3.175×10⁻₂ mol

Since the stoichiometry of the reaction between calcium and EDTA is 1:1, the number of moles of EDTA is also 3.175×10⁻₂ mol.

To find the molarity of the EDTA solution, we divide the number of moles of EDTA by the volume in liters:

Molarity of EDTA = Moles of EDTA / Volume (in liters) = 3.175×10⁻₂ mol / 0.02014 L = 0.1579 M

Answer 2

The molarity of the EDTA solution is found by dividing the moles of EDTA (1.27×10⁻³) by its volume in liters (0.02014 L), resulting in a molarity of 0.06308 M at the equivalence point.

Step-by-step explanation:

To determine the molarity of the EDTA solution used to titrate the calcium solution, we first note that the equivalence point was reached after adding 20.14 milliliters (mL) of EDTA. At this point, the number of moles of EDTA equals the number of moles of calcium because EDTA and calcium react in a 1:1 molar ratio. Given that there are 1.27×10⁻³ moles of calcium, this is also the number of moles of EDTA used.

We then calculate the molarity (M) of EDTA using the formula M = moles/volume (in liters). Converting 20.14 mL to liters (0.02014 L), we find the molarity:
M = (1.27×10⁻³ mol) / (0.02014 L) = 0.06308 M (rounded to five significant figures). Therefore, the molarity of the EDTA solution is 0.06308 M.