A) The Eriochrome Black T indicator is mistakenly omitted. what is the color of

Question

A) The Eriochrome Black T indicator is mistakenly omitted. what is the color of the analyte (standard Ca^2+ solution)?

Describe the appearance of the analyte with the continued addition of the Na^2H^2Y solution? Explain?

B) The Dispensing of the Na^2H^2Y solution from the buret is discountinued when the solution turns purple. Because of this technique error, will the reported molar concentration of the Na^2H^2Y solution be too high, too low, or unaffected?

C) The Dispensing of the Na^2H^2Y solution from the buret is discountinued when the solution turns purple. Because of this technique error, will the reported hardness of the water sample be too high, too low, or unaffected?

Explanation / Answer

a) EBT is used as indicator to identify the end point of the titration.If we add EBT then it will give blue colour at the end point. If we dont add EBT then the solution will remain colourless on addition of EDTA, as the complex formed by EDTA with Calcium ion is colourless unlike EBT which forms wine red coloured complex with Calcium ion

b) At the end point of the titration, blue colour is observed when all the Calcium ions are complexed with EDTA. The excess EBT then shows blue colour. so if we stop the dispensing of the Na^2H^2Y solution from the buret when we obtain a persistant purple colour (or blue colour), it shows that the reaction is almost complete hence it will not affect the concentration.

c) As the concentration of Na^2H^2Y solution is not affected, the hardness of water will also be not affected.

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