Colorimetric Analysis Procedure Quiz

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What is the purpose of evaporating the contents to dryness on a sand bath?

To remove impurities from the sample
To prevent contamination during further processing
To concentrate the silica for accurate weighing (correct)
To dissolve the residue in hydrofluoric acid

Why is it important to heat the crucible containing the residue slowly at first before heating finally at 1000 ℃?

To ensure complete combustion of the sample
To prevent the crucible from breaking due to sudden temperature changes (correct)
To speed up the process of residue formation
To avoid loss of volatile components

What is the purpose of fusing the residue with potassium bisulphate after hydrofluoric acid treatment?

To convert silica into a soluble form (correct)
To remove impurities from the residue
To dilute the residue for ease of handling
To increase the weight of the residue

Why is it necessary to cool and dilute the solution to 250 ml in a calibrated flask during the preparation of the Stock solution?

To ensure uniformity in sample preparation (B) Signup and view all the answers

Why is ascorbic acid added after oxalic acid in the determination process?

To act as a reducing agent to stabilize molybdenum (A) Signup and view all the answers

What is the purpose of adding ammonia until the color changes to red during the photometric method of residual silica determination?

To maintain a constant pH throughout the analysis (C) Signup and view all the answers

What is the purpose of allowing the solution to stand for half an hour?

To develop full color for measurement (B) Signup and view all the answers

In the determination of silica, why is a test blank solution used?

To compare and convert the photometric reading (D) Signup and view all the answers

What is the purpose of acidifying the solution with a few drops of HCl in the presence of a phenolphthalein indicator?

To aid in the determination of silica (C) Signup and view all the answers

How is the total amount of silica in the test solution calculated?

% SiO2 = A x 250 x 100 x 100 / 10 x W x 1000000 (C) Signup and view all the answers

Why is methyl orange indicator added before performing complexometric EDTA titration for alumina determination?

To indicate color change during titration (C) Signup and view all the answers

What is the function of ammonia (1:3) during alumina determination using complexometric EDTA titration?

To change the color of the solution from red to yellow (B) Signup and view all the answers

What is the purpose of adding fusion mixture (Na2CO3 and K2CO3) to the silica sample before fusing in a muffle furnace?

To increase the melting point of the sample (D) Signup and view all the answers

Why is it important to heat the crucible in a muffle furnace at approximately 1000℃ after fusing the silica sample?

To ensure complete fusion of the sample (C) Signup and view all the answers

Why is it necessary to heat the crucible in a water bath until the smell of HCl is no longer detected?

To remove any residual hydrogen chloride gas (C) Signup and view all the answers

Why is it essential to wash the residue three times with hot HCl and then with hot water?

To prevent chloride contamination (C) Signup and view all the answers

What is the purpose of transferring the paper along with the filtrate to an ignited and tared Pt-crucible?

To burn off any remaining paper fibers (A) Signup and view all the answers

Why is it crucial to heat the Pt-crucible in a muffle furnace at 1175 - 1200℃ after igniting at a low temperature?

To reach a constant weight of the silica residue (D) Signup and view all the answers