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ACID·BASE TITHATION

f. PROCEDUREA. CLEANING OF THE nURETS

Clean the base (rubber-tipped) and the acid (glass-tipped) burets WiOI soap and water and rinse very wellwith distilled water. Invert the burets and clamp them on the buret stand.

B. PREPARATION OF AN OXALIC ACID SOLUTION ..J. Weigh in a clean dry beaker 1.5 gram of pure oxalic acid crystals (COOH)z':2H10 to the last decimal

. place possible on your balance. .2. Dissolve the acid crystals in 50.00 mL distilled water. Transfer the acid solution to 150-mL

volumetric flask, taking care to avoid any losses. .3. Rinsethe beaker with distilled water and trail-firerthe rinsings to the flask. Add enough distilled water

to fill the flask up to the marie Stopper the flask and mix the solution well by swirling and invertingthe flask repeatedly. .

4. Calculate the molarity of the acid solution. Write it on the label of the flask.

C. PREPARATION OF A NlIOH SOLUTIONI. Repeat steps t - 4lnD but use 3.18 grams of NaOH and a 25O-mL flask instead of the oxalic acid

crystals and the 150-ntL flask. respectively.2. Transfer the NaOn solution to a clean dry coke bottle. Stopper and label the bottle.

D. niRATION OF OXALIC ACID WITHN.On SOLUTION1. Using a dry funnel. rinse the base and the add burets with tile prepared NaOH and the oxalic acid

solutions, respectively. Discard the rinse.2. Fill each buret beyond the zero reading with the corresponding solution.3. Open the stopcock of the buret and allow all air bubbles at tho tip to escape out. Adjust the level of

the solution inside tile buret tothe zero mark. Record this Il.'Ithe initial buret reading.4. Run 50.00 ml. of the acidsolution into a 250'i'llL Erlenmeyer flask, and dilute the solution to 150.0

mL with distilled water. Add 1 drop! or phenolpthaleln indicator. Place the flask under the tipofthe base buret containing the NaOH solution (titrant) and titrate the acid as follows:

a. Run 2-mL portions of the titrant from the buret into the flask under it, swirling the flask gentlybut continuously to ensure proper mixing. Avoid loss of solution from spattering.

b. When the change in color that forms after each addition of titrant persists longer beforedisappearing, Add the titrant dropwise, swirling continuously.

c. finally, when the color takes longer to disappear, add the titrant 1l19w1y by drops with constantswirling. Watch fur the faintest red color of solution. .

d. When the color change persists despite swirling for at least 15 seconds, note the final buretreading. Add one Of more drop of titrant; ifa distinct color change is observed, the finalreading marks the end point of the titration, Read buret volumes to two decimal places.

5. Calculate the molarity of the NaOH solution. Write it on the label of the bottle.,

II. DATA AND RESUl,TS.Mass of oxalic acid dihydrate. (COOHh.2fhO t:I

Initial base buret reading :1 _ --

Final base buret reading= . .

In. REAcnON: {COOHh.2H10 + 2NaOH :: (COONs) 1 + 41hO

IV. CALCULArions,L Mole ratio of acid to base nNnn <,::.

2. Molar mass p£ (COOHh2H10 = -=3. No. of moles ofNnOH in the volume of titrant used =

4. No of moles of oxalic acid used =-5. t-.tolarity ofNaOH solution =: ._.

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V. DISCUSSIONS:1. Vv11Y should the buret be completely drained of the rinse water or rinserl with the

titrant before filling it with titrant?2. 'The amount of water added to dissolve the oxalic acid dihydrate crystals did no!

have to be accurately measured and could be :1I1)' volume. Why is the volume ofthe resulting oxalic acid solution not important ill tile computations?

3. It is good practice to wait a few seconds afler addingto or removing any volume'from-the titrant inside the buret before doing the new volume re;:uiing·. Why?

4. a possible source of error in titration is parallax.n. \\1IIItis p nrall ux'ih. How does the parallax affect the vohuue rending if the eye is above or

below Ole level of the liquid inside the buret?c. How can parallax" errors in volume readings bE' avoided?

5. What important property should oxalic acid dihydrate or any other substance haveso that it can be used as 9. standard in determining unknown-concentrntions oflitrants to be used in titration dterminations?

6. what is Ole molarity of your standard NaOH solution?

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