Question

The average EDTA concentration after being standardized was calculated to be 0.02018 M and you used 13.56 ml to reach the endpoint with 25ml of your unknown. What is the ppm of CaCO₃ in the unknown? (Formula wt of CaCO₃ = 100.08g/mol)

Answer 1

The concentration of CaCO₃ in the unknown solution is calculated to be 1094.92 ppm. This is done by using the molarity of standardized EDTA multiplied by the volume used to titrate 25 mL of the unknown, converting moles of EDTA to mass of CaCO₃, and then calculating the ppm.

Step-by-step explanation:

To calculate the parts per million (ppm) of CaCO₃ in the unknown, first determine the moles of EDTA used in the titration:

• Moles of EDTA = Molarity of EDTA × Volume of EDTA (in liters)
• Moles of EDTA = 0.02018 M × 0.01356 L
• Moles of EDTA = 0.0002736438 mol

Since the mole ratio of CaCO₃ to EDTA is 1:1, the moles of CaCO₃ in the unknown solution is also 0.0002736438 mol. To find the mass:

• Mass of CaCO₃ = Moles of CaCO₃ × Molar Mass of CaCO₃
• Mass of CaCO₃ = 0.0002736438 mol × 100.08 g/mol
• Mass of CaCO₃ = 0.027373 g

Finally, to convert the mass of CaCO₃ to ppm in the original 25 mL of the unknown:

• ppm CaCO₃ = (Mass of CaCO₃ in grams / volume of solution in liters) × 1,000,000
• ppm CaCO₃ = (0.027373 g / 0.025 L) × 1,000,000
• ppm CaCO₃ = 1094.92 ppm

Thus, the concentration of CaCO₃ in the unknown solution is 1094.92 ppm.