Titration technique Knowledge-Based Practice

Questions

1. 1.

   Why is an Erlenmeyer flask preferred over an open beaker as the receiving vessel during a manual volumetric titration?

   • A) It accelerates the rate of the neutralization reaction by concentrating the vapor phase above the solution.
   • B) It permits the direct and highly accurate measurement of the initial analyte volume using the flask's printed graduations.
   • C) It prevents atmospheric carbon dioxide from dissolving into the solution without requiring a stopper.
   • D) It allows vigorous swirling to ensure rapid mixing while minimizing the risk of solution splashing out of the vessel.
2. 2.

   When delivering an aliquot of analyte solution into an Erlenmeyer flask using a volumetric transfer pipette calibrated "to deliver" (TD), how should the small residual droplet remaining inside the pipette tip be handled?

   • A) It should be forcefully expelled into the flask using a pipette bulb to ensure full transfer of the liquid volume.
   • B) It should be allowed to remain in the tip, after briefly touching the pipette tip to the inner wall of the receiving flask.
   • C) It should be flushed into the receiving flask by drawing deionized water into the pipette and dispensing it.
   • D) It should be shaken vigorously downwards over the flask opening until the droplet is dislodged into the solution.
3. 3.

   What systematic error occurs if an air bubble trapped in the burette tip below the stopcock is dislodged and expelled during a volumetric titration?

   • A) The recorded volume of titrant delivered is falsely low because the bubble impedes the downward flow of liquid.
   • B) The concentration of the titrant decreases because atmospheric gases dissolve into the exiting stream.
   • C) The recorded volume of titrant delivered is falsely high because the volume vacated by the bubble is measured as delivered titrant.
   • D) The pH of the analyte solution changes prematurely due to the introduction of pressurized air into the flask.
4. 4.

   During a volumetric titration, why is it acceptable practice to periodically wash down splashes on the inner walls of the receiving Erlenmeyer flask with deionized water?

   • A) It increases the sensitivity of the indicator by adjusting its transition range.
   • B) It does not change the total number of moles of analyte present in the flask.
   • C) It keeps the concentration of the analyte constant throughout the titration process.
   • D) It neutralizes residual titrant adhering to the glass surface above the liquid level.
5. 5.

   Which procedure should be followed when preparing a glass burette with a standard titrant solution prior to conducting a volumetric titration?

   • A) Rinse the burette with deionized water followed by small portions of the titrant solution, and ensure the tip below the stopcock is free of air bubbles.
   • B) Rinse the burette solely with deionized water and immediately fill it to the zero mark while the inner walls are still wet.
   • C) Rinse the burette with the analyte solution before filling it with titrant to condition the glass surface.
   • D) Fill the burette with titrant without pre-rinsing and allow any air bubble trapped in the tip to be expelled during the titration run.

Answers and step-by-step solutions appear after you finish the test.