Question2. In an experiment to determine the water hardness of tap water, a researcher measured three 50 mL aliquots of water samples and to each sample he added 10 mL of pH 10 ammonia/ammonium chloride buffer and two drops of eriochrome black T indicator and the colour changed to wine red. The resulting solutions were then separately titrated against 0.05 M sodium-EDTA solution from the burette until a final endpoint colour change. The data obtained was recorded in a table as shown below. \begin{tabular}{|l|l|l|l|} \hline Titration & 1 & 2 & 3 \\ \hline final reading $/ \mathrm{mL}$ & 10.70 & 10.65 & 10.60 \\ \hline Initial reading $/ \mathrm{mL}$ & 0.00 & 0.00 & 0.00 \\ \hline Titre value $/ \mathrm{mL}$ & & & \\ \hline \end{tabular} a) What is the expected endpoint colour change? b) Calculate the average titre of the results? c) Write a balance equation of reaction between calcium ions and EDTA d) Calculate the number of moles of EDTA used in each titration and the average number of moles for the whole process. e) What is the concentration of $\mathrm{Ca}^{2+}$ (expressed as $\mathrm{ppm} \mathrm{CaCO}_{3}$ ) in the sample?