Uses in Qualitative and Quantitative Analysis — Prelims Questions

Which of the following reagents is specifically used for the qualitative detection of Ni$^{2+}$ ions, forming a characteristic red precipitate?

A $20,\text{mL}$ sample of hard water requires $15,\text{mL}$ of $0.01,\text{M}$ EDTA solution for complete titration. Calculate the total hardness of the water in terms of ppm of CaCO$_3$. (Molar mass of CaCO$_3 = 100,\text{g/mol}$)

Which of the following statements regarding the 'chelate effect' is INCORRECT?

Which metal ion forms a deep blue solution upon reaction with excess aqueous ammonia?

Nessler's reagent is used for the detection of which of the following species?

In the spectrophotometric estimation of iron, Fe$^{3+}$ is first reduced to Fe$^{2+}$ and then reacted with 1,10-phenanthroline. What is the primary reason for this reduction step?