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Chemistry: Acid-Base Titration Essay, Research Paper

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.


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