AcidBase Titration

Chemistry

Acid-Base Titration

Purpose:
The objective of this experiment were: a) to review the concept of simple acid-base reactions; b) to review the stoichiometric calculations involved in chemical reactions; c) to review the basic lab procedure of a titration and introduce the student to the concept of a primary standard and the process of standardization; d) to review the calculations involving chemical solutions; e) to help the student improve his/her lab technique.

Theory:
Titration was used to study acid-base neutralization reaction quantitatively. In acid-base titration experiment, a solution of accurately KHP concentration was added gradually to another solution of NaOH concentration until the chemical reaction between the two solutions were completed. The equivalence point was the point at which the acid was completely reacted with or neutralized by the base. The point was signaled by a changing of color of an indicator that had been added to the acid solution. Indicator was substance that had distinctly different colors in acidic and basic media. Phenolphthalein was a common indicator which was colorless in acidic and neutral solutions, but reddish pink was result in basic solutions. Strong acid (contained H+ ion) and strong base ( contained OH ) were 100% ionized in water and they were all strong electrolytes.
Procedure:
Part A.
Investigating solid NaOH for use as a possible primary standard
First of all, The weight of a weighting paper was measured in analytical balance, then added two pellets of NaOH and reweighed the total amount of those. At the end of the lab, reweighed the combination and recorded all results in the lab manual.
Part B.
Preparation and standardization of a solution of sodium hydroxide
A clean beaker, burette, three 250ml Erlenmeyer flasks, and florence flask were rinsed by soap and distilled water. Poured 1.40g of NaOH into florence flask and added 350ml distilled water, then swirl it and inverted flask five times with parafilm on the top of it. Next, obtained a vial of KHP from the instructor, and poured about 0.408g into three different Erlenmeyer flasks by measuring with analytical balance. Then, filled up about 25ml of distilled water, added 3 drops of phenolphthalein into it and mixed them well by a glass rod. Labeled all solutions to prevent mix them up. Before the titration began, the buret should be rinsed with NaOH solution and recorded the initial buret reading. Titrated the solutions until the reddish pink color appeared. Recorded the final reading, and calculated the change of volume.
Part C.
Determination of the molar mass of unknown acid
Repeated the procedure above, but this time KHP was replaced with an unknown acidic solution and concentration. Demanded the number of replaceable hydrogen from the instructor.

Conclusion and Discussion:
From the titration results of three trial, the average of molarity of NaOH is 0.1021 . The percentage deviation in molarity of NaOH had 0.20% error. The possible error in this experiment were: the error in taking the buret readings, the error in measuring amount of elements, and the NaOH was not stable under air.