Chemistry question please :how to calculate the concentration of water hardness’ in this tap water, in ppm?
EDTA is ethylene diamine tetra-acetic acid. It sequesters calcium salts in the water.(Bonds to them so they cannot react with anything else.) Concn of EDTA = 5.06 gpl = 0.0506 gram per ml 6.5 times 0.0506 grams = 0.3289 grams EDTA used in the titration 100ml of water has an EDTA titre of 0.3289 grams of EDTA 1 gram EDTA equivalent of calcium is present in 100 / 0.3289 ml of water = 304.04 ml of water = 304.04 grams of water (1ml of water has a mass of 1 gram) = 1 part in 304.04 = 1 000 000 / 304.04 ppm =3289.04 ppm Burettes cannot be read to that degree of accuracy, and a low burette reading like 6.5 ml cannot be accurate to more than two significant figures. For a more accurate figure the EDTA could be made four times weaker so a result close to 25ml is obtained and a half-division error in reading the result makes less percentage error in the figure than at 6.5ml. The result should not ‘invent’ accuracy that isn’t known and would be quoted by a laboratory technician as 3290ppm. equiv
