An EDTA solution was prepared by dissolving approx 4g of the disodium salt in ap

Question

An EDTA solution was prepared by dissolving approx 4g of the disodium salt in approx 1L of water. An average of 42.35mL of this solution was required to titrate 50.00mL aliquots of a standard that contained 0.7682g of MgCO3 per liter. Titration of 25.00mL sample of mineral water at pH 10 required 18.81mL of the EDTA solution. A 50.00mL aliquot of the mineral water was rendered strongly alkaline to precipitate the magnesium at Mg(OH)2. Titration with the calcium specific indicator required 13.54mL of the EDTA solution. Calculate the molarity of the EDTA solution, the concentration of CaCO3 in the mineral water(ppm), and the concentration of MgCO3 in the mineral water(ppm). I need alot of help. I need to see steps and explanations for them. Thanks

Explanation / Answer

This is a complexation titration, not a precipitation.

EDTA reacts in a 1:1 ratio with both calcium and magnesium. First, determine how many moles of MgCO3 were in the standard, and from that, you can use the V1M1n2 = V2M2n1 formula to determine the molarity of the EDTA solution.

You use the formula again for the total Ca/Mg content of the mineral water, as well as the Ca content. Subtract the Ca content from the total and you will get the Mg content.

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