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Experiment 11: Titration

Procedure

A. Preparation of Sodium Hydroxide Solution

In a beaker prepare 300mL of 0.10M sodium hydroxide from the solid. Record the mass of the sodium hydroxide to as many decimal places as you can.(Note how the numbers on the balance are increasing.)Be sure to stir it well!

B. Standardization of Sodium hydroxide solution

1. Weigh out about 0.15g of solid oxalic acid and dissolve it in about 20mL of deionized water inan Erlenmeyer Flask. Record the actual mass.

2.Add about 5 drops of phenolphthalein to the solution.

3. Clean a burette and rinse it out with deionized water.With the stopcock open, run some of your sodium hydroxide solution down the inside and allow it to drain. Fill your burette with your sodium hydroxide solution and record the volume.Make sure there are no air bubbles, especially in the tip.

4. Titrate the sodium hydroxide into the acid solution until the color changes and record the final volume.

5.Repeat this procedure three times.

C. Determination of Unknown

1. Obtain a test tube of unknown hydrochloric acid and record the unknown number.

2. Using a volumetric pipette, add 10.00mL of your unknown to an Erlenmeyer flask.

3. Add a few drops of phenolphthalein.

4. Titrate with your standardized sodium hydroxide from part B recording the initial and final volumes.

5. Repeat this procedure for a total of three trials.(If there is not enough unknown to do three trials of 10.00mL each, use 5mL for the last trial.Obtain a 5 mL volumetric pipette for the sample.)

DISPOSE OF YOUR NEUTRALIZED SOLUTIONS IN THE BLUE WASTE CONTAINER.

DISPOSE OF THE LEFTOVER ACID IN THE YELLOW WASTE CONTAINER.
DISPOSE OF THE LEFTOVER BASE IN THE PINK WASTE CONTAINER.

Links to Procedural Videos:

Procedure Part B:

Procedure Part C:

Name_____________________________________________Section ____________________

Experiment 12

Titration

A. Preparation of Sodium Hydroxide Solution

Mass of sodium hydroxide desired (show work) ________

Mass of sodium hydroxide used _____________

B. Standardization of Sodium Hydroxide Solution (Show Work)

Balanced chemical equation:____________________________________________________

Trial 1Trial 2Trial 3

Mass of oxalic acid__0.1445 g___0.1520 g___0.1489 g_

Initial burette reading__0.64 mL___0.14 mL___1.24 mL_

Final burette reading_22.55 mL__22.75 mL__23.25 mL_

Volume NaOH added _____________________________

moles of oxalic acid_____________________________

moles of NaOH added_____________________________

Molarity of NaOH_____________________________

Average Molarity__________

C. Determination of Unknown (Show Work)

Balanced chemical equation:___________________________________________

Unknown number _NA_____

Trial 1Trial 2Trial 3

Volume of unknown HCl

titrated_10.00 mL__10.00 mL__10.00 mL_

Initial burette reading __1.50 mL___0.28 mL_ __2.23 mL_

Final burette reading_34.85 mL__33.60 mL_ _35.70 mL_

Volume NaOH added__________ __________________

moles NaOH added ____________________________

(Use average molarity from part B

and multiply it by the volume you added)

moles HCl____________________________

molarity of HCl____________________________

Average molarity__________

Actual Molarity (from instructor) __0.3665M_

percentage error ___________

QUESTIONS:

1.From the SDS, what is another name for sodium hydroxide?

2. Why will the phenolphthalein eventually fade?Show reactions.

3.Why do we titrate into a flask instead of a beaker?

4. What effect would each of the following errors have on the determined concentration of the unknown acid? (Would the calculated value be too high, too low or unchanged?) Explain your reasoning in each case.

a. The mass of the oxalic acid was recorded to low.

b. The unknown acid was added to a flask containing 35 mL of water.

c. The final volume in the standardization was recorded too high.

d. The final volume in the determination of the unknown acid was recorded too low.

5. The concentration of an unknown sample of sulfuric acid was determined by the method used in this experiment, using two sets of titrations.In the first titration the sodium hydroxide was standardized by titrating 0.1852g of oxalic acid dihydrate (molar mass = 126.07g/mole) with 32.30mL of sodium hydroxide solution.In the second titration 10.00mL of the unknown sulfuric acid solution was titrated with 12.85mL of the sodium hydroxide solution.What was the concentration of the sulfuric acid?(Show your work!!)

Discussion:

Discuss why your calculated value for the unknown differs from the acutal.List of all possible sources of error and what can be done to avoid these errors.

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