Colorimetric Determination of Silica Quiz

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What is the purpose of allowing the solution to stand for half an hour before measuring optical density?

To speed up the optical density measurement
To dilute the sample solution
To enhance the color development process (correct)
To decrease the color intensity

In the determination of silica, why is a test blank solution prepared in the same way as the sample solution?

To dilute the sample solution
To measure the optical density at a different wavelength
To speed up the calibration process
To provide a reference point for comparison (correct)

What is the purpose of establishing a calibration graph in the determination of silica?

To measure the pH of the solution
To relate optical density to known concentrations of silica (correct)
To speed up the dilution process
To remove impurities from the sample

Why is EDTA solution added in the determination of silica?

To form a complex with metal ions (B) Signup and view all the answers

What happens when ammonia is added in the determination of alumina using complexometric EDTA titration?

The solution changes color from red to yellow (C) Signup and view all the answers

Why is buffer solution added before titration in determining alumina?

To maintain a constant pH for accurate titration (A) Signup and view all the answers

What is the purpose of adding 5 drops of HNO3 (1:1) and 10 ml HF in the initial step?

To dissolve impure silica (C) Signup and view all the answers

Why is the residue heated slowly at first and then finally for 2 mins at 1000 ℃?

To ensure complete combustion (A) Signup and view all the answers

What is the purpose of fusing the residue with potassium bisulphate?

To determine silica impurities (D) Signup and view all the answers

In the determination of residual silica, why is phenolphthalein added until the color changes to red?

To detect the endpoint of the titration (A) Signup and view all the answers

What is the purpose of adding ferric ammonium sulphate in the determination of residual silica?

To form a complex with silica (B) Signup and view all the answers

Why is ascorbic acid added after oxalic acid in the determination of residual silica?

To prevent oxidation of iron (III) (D) Signup and view all the answers

What is the purpose of adding a fusion mixture (1:1 mix of Na2CO3 and K2CO3) during the determination of major silica?

To provide a medium for the fusion process at high temperature (A) Signup and view all the answers

Why is it essential to heat the crucible in a muffle furnace at ~1000℃ after fusing with the fusion mixture?

To remove carbonaceous matter (C) Signup and view all the answers

What is the purpose of digesting the sample in a water bath for 10 minutes after dissolving soluble salts?

To ensure complete dissolution of all soluble salts (A) Signup and view all the answers

What is the reason for filtering with No. 41 Whatman Filter paper after digesting the sample?

To remove insoluble impurities (B) Signup and view all the answers

Why is it necessary to wash the residue three times with hot HCl (1:20) after filtration?

To neutralize excess base from the fusion mixture (A) Signup and view all the answers

What is the purpose of igniting at low temperature before heating in a muffle furnace at 1175 – 1200 ℃ during constant weight determination?

To remove volatile compounds (C) Signup and view all the answers