In an experiment to determine the total hardness of a water sample containing both calcium and magnesium ions, a solution of the reagent edta (ethylene diamine tetraacetic acid) in the form of its disodium salt (represented by Na2H2Y) is titrated against a sample of the water using a suitable indicator - Leaving Cert Chemistry - Question 1 - 2004

To rinse the burette, first, ensure that the burette is clean. Then, fill it with deionized water and let it run through the tap to remove any residues. After that, rinse it three times with the edta reagent: fill it with a small amount of the reagent, allowing it to coat the inside walls before emptying it out through the tap. Finally, fill the burette with the edta solution again, ensuring no air bubbles are present. Clamp the burette vertically and set the liquid level to zero before titration.

A buffer solution must be added before carrying out the titration. This is necessary to maintain the pH of the solution above 9, which ensures the indicator works correctly and that the endpoint is sharp and accurate.

To calculate the total hardness expressed in terms of CaCO3, use the formula: ext{Total Hardness} (ppm) = rac{0.801 ext{ mol dm}^{-3} imes 100 ext{ cm}^3 imes 100 ext{ g}}{1 ext{ mol dm}^{-3}} The total hardness converts to about 98 ppm when processed through the correct calculation.

To convert the total hardness to grams per litre, apply the formula: ext{Hardness (g/L)} = ext{Total Hardness (ppm)} imes rac{1 g}{1000 ppm} Thus, it equals approximately 0.098 g/L.

The ppm of hardness in the water can also be stated as the following: ext{ppm} = rac{0.098 g/L imes 1000}{100 g ext{ per mole of CaCO3}} This results in approximately 98 ppm.

The balanced equation for the reaction when the whitish deposit (mostly consisting of calcium carbonate) dissolves in dilute hydrochloric acid is: $ext{CaCO}_3 (s) + 2 ext{HCl} (aq) \rightarrow ext{CaCl}_2 (aq) + ext{H}_2 ext{O} (l) + ext{CO}_2 (g)$