“A Titration Competition” – Lab #8
1. Since all solutions and aqueous solutions have their own pH, it is important for all glassware to be clean and dry before performing a titration. Even a slight trace of a different solution could alter the pH and give an inaccurate titration reading. If the glassware is not completely dry after rinsing, the small traces of water could make the solution more dilute than it should be thus changing its concentration.
2. Air bubbles in the burette tip is a possible source of error because it can cause a misreading in the amount of solution used since the air bubbles take up space. If the air bubbles are not removed, you will get a volume reading greater than the actual amount of standard solution used. To remove air bubbles from the burette tip, open the stopcock and run the fluid through until there are no more bubbles. Bubbles in the burette tip can usually be removed by tapping the side of the burette while the stopcock is open.
3. To indicate the endpoint of his titration, Dr. Sweeney would have observed a slight change in color from colorless to pink that lasts at least 30 seconds and does not fade away. The desired end point in a phenolphthalein titration is “a pale pink tint that persists for 30 seconds.” It took Dr. Sweeney 24mL of NaOH to reach his endpoint.
4. HClO4(aq) + NaOH(aq) ? NaClO4(aq) + H2O(l)
5. This is an acid-base reaction (neutralization reaction). Neutralization reactions involve the reaction of an acid with a base to form a salt.
6. M1V1 = M2V2
(24mL)(0.040M) = (M2)(20mL)
(0.96 mL*M) = (M2)(20mL)
(0.96 mL*M)/(20mL) = M2
M2 = 0.048M HClO4