Homework Help: CHEM AB HELP ASAP

Posted by Lesle on Wednesday, October 17, 2012 at 3:17am.

I have a pre lab questions that are due in a few hours and I need help. Theres several questions

In the titration of 25.00 ml of a water sample, it took 20.590 ml of 4.995x10-3 M EDTA solution to reach the endpoint.

The total hardness is due to one or a combination of Ca2+, Mg2+, and Fe2+ in your sample. It is convenient to express this hardness as though it was entirely due to Ca2+. Making this assumption, determine the number of moles of Ca2+ present in the bottled water sample titrated.
The total hardness is always listed in parts-per-million (ppm) of CaCO3 (or mg CaCO3 / Kg H2O). Since the density of water is 1.0 g/ml, one ppm would be the same as the number of mg of CaCO3 per liter of water. Determine the number of moles of CaCO3 present in the titrated sample of water, assuming that all the Ca2+ combines with CO32−.

Calculate the number of grams of CaCO3 present and convert to mg.

Convert the number of ml of bottled water used in eache sample titration to Liters.

Calculate the ppm of CaCO3 = mg CaCO3 / Liters H2O used.

CHEM AB HELP ASAP - DrBob222, Wednesday, October 17, 2012 at 3:11pm
mols EDTA = M x L = ?
mols Ca^2+ = same as mols EDTA

g CaCO3 = mols x molar mass CaCO3. That's g CaCO3 in 25.00 mL.
Convert that to mg/L for ppm CaCO3.

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