Question

a sample solution of hno₃(aq) and the indicator bromothymol blue were titrated with naoh(aq).
titration procedures
i rinse the erlenmeyer ask with naoh(aq).
ii rinse the burette with distilled water, then with naoh(aq).
iii rinse the burette with naoh(aq), then with distilled water.
iv expel air bubbles from the burette tip by allowing some naoh(aq) solution to run through it.
in preparation for titration with naoh(aq), the procedures that are part of proper titration technique are
i and ii
iii and iv
i and iii
ii and iv

Explanation:

To determine proper titration techniques:

• Procedure I: Rinsing the Erlenmeyer flask with $\ce{NaOH_{(aq)}}$ is incorrect. The flask should be rinsed with the solution to be titrated ( $\ce{HNO_{3(aq)}}$ ) or distilled water, not the titrant ( $\ce{NaOH_{(aq)}}$ ), as this would alter the amount of the substance to be titrated.
• Procedure II: Rinsing the burette with distilled water first (to clean it) and then with $\ce{NaOH_{(aq)}}$ (to ensure the burette is coated with the titrant and its concentration remains accurate) is correct.
• Procedure III: Rinsing the burette with $\ce{NaOH_{(aq)}}$ first and then distilled water is incorrect. This would dilute the $\ce{NaOH_{(aq)}}$ in the burette, changing its concentration.
• Procedure IV: Expelling air bubbles from the burette tip by running some $\ce{NaOH_{(aq)}}$ through it is correct. Air bubbles in the burette tip can lead to inaccurate volume readings.

So the correct procedures are II and IV.

Answer:

II and IV