Determination of the concentration of HCl: Pipette 10 mL of hydrochloric acid and transfer to a 100 mL volumetric flask, complete the volume with water and homogenize. Remove a 10 mL aliquot of this solution and transfer it to a second dilution in a 100 mL volumetric flask, complete the volume with water and homogenize. Take a 20 mL aliquot of this last solution and transfer to a 250 mL erlenmeyr and add 20 mL of distilled water and 4 drops of the acid-base indicator. Titrate with a previously standardized 0.100 mol/L sodium hydroxide solution until the indicator turns.” Answer: a) In this titration, the indicator used is phenolphthalein. Discuss the use of this indicator considering its turning range and pH at the stoichiometric point of the titration. Justify. b) Considering that the volume of titrant used was equal to 24.5 mL, calculate the concentration of HCl in the sample in mol/L.
Considering the procedure below: “Determination of the concentration of HCl: Pipette 10 mL of hydrochloric acid and transfer to a 100 mL volumetric flask, complete the volume with water and homogenize. Remove a 10 mL aliquot of this solution and transfer it to a second dilution in a 100 mL volumetric flask, complete the volume with water and homogenize. Take a 20 mL aliquot of this last solution and transfer to a 250 mL erlenmeyr and add 20 mL of distilled water and 4 drops of the acid-base indicator. Titrate with a previously standardized 0.100 mol/L sodium hydroxide solution until the indicator turns.” Answer: a) In this titration, the indicator used is phenolphthalein. Discuss the use of this indicator considering its turning range and pH at the stoichiometric point of the titration. Justify. b) Considering that the volume of titrant used was equal to 24.5 mL, calculate the concentration of HCl in the sample in mol/L.
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