UPSC Combined Geo-Scientist, Mains · 2019 · Mains Paper III

Q2(c). Why Eriochrome Black T fails for Cu²⁺, Ni²⁺, Co²⁺, Cr³⁺, Fe³⁺, Al³⁺

5 marks
Topic: Analysis of geological materials
Question only

Question

In a direct titration of Cu²⁺, Ni²⁺, Co²⁺, Cr³⁺, Fe³⁺ and Al³⁺ with EDTA, Eriochrome Black T cannot be used as an indicator. Why?

Model answer

The free solution for 2019 answers questions 1, 3, 4, 6, 7 and 10, the ones picked in its time plan. This part is not answered on the site yet. New answers are announced on Telegram.

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Coversindicator blockingEriochrome Black TEDTA titrationback titration

All parts of Question 2

2(a) Degree of hydrolysis and pH of 0.01 M Na₂CO₃10 marks
2(b) Bringing a sparingly soluble salt into solution10 marks
2(c) Why Eriochrome Black T fails for Cu²⁺, Ni²⁺, Co²⁺, Cr³⁺, Fe³⁺, Al³⁺5 marks
2(d) Errors in iodine titrations with starch5 marks