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.

Category: Science