Experiment 5 NaOH Standardization

Valdosta State University

Experiment 5NaOH Standardization



Purpose

To accurately determine the concentration of a sodium hydroxide solution by titration.



Background

Base Standardization

Process of accurately determining the concentration of a base by reacting it with a known quantity of acid (KHP).

KHC8H4O4(aq) + NaOH(aq) KNaC8H4O4(aq) + H2O(l)

KHC8H4O4 - Potassium Hydrogen Phthalate (KHP)



Background

• In a titration, a known mass of KHP is reacted with just enough NaOH to neutralize it.

• The equivalence point occurs when just enough NaOH has been used to neutralize the KHP.

• The equivalence point is not always visible; so, an indicator is added.



Background

• The equivalence point and the endpoint are independent chemical reactions.– the equivalence point occurs at the neutralization of the acid.– the endpoint occurs at the neutralization of the indicator.

• A good standardization depends on the proper selection of an indicator.

• For this experiment (strong base, weak acid) phenolphthalein is a good selection.


IndicatorA substance, usually a weak acid, which changes color in response to pH.


Procedure – Experiment 5

- For this experiment, work individually (i.e. groups of one).


Technique - Titration

Clean The Buret1. Rinse a buret twice with distilled water. 2. Rinse the buret twice with 10-mL portions of your

prepared NaOH solution. 3. Run some of your prepared NaOH solution through

the tip of the buret. 4. Drain the buret, then fill it with your prepared NaOH

solution. 5. Let some of your prepared NaOH solution run through

the tip of the buret so that all air bubbles are removed.



Clean The Buret



Prepare the KHP1. Weigh 0.4 g to 0.5 g of KHP to the nearest 0.001 g

into each of three 125-mL Erlenmeyer flasks. 2. Add approximately 30 mL of distilled water to each

flask and stir well until all KHP is dissolved. 3. Add three drops of phenolphthalein indicator to each

Erlenmeyer flask.



Performing The Experiment1. Record the volume of NaOH in the buret.



Performing The Experiment1. Record the volume of NaOH in the buret.2. Start adding NaOH, swirling the flask during the

addition.



Performing The Experiment1. Record the volume of NaOH in the buret.2. Start adding NaOH, swirling the flask during the

addition.3. As a pink color appears, the addition of NaOH is

slowed.4. As the pink color becomes more persistent, slow the

addition further.5. Stop the addition when the pink color persists for five

seconds.6. Record the volume of NaOH in the buret.



Performing The Experiment6. Record the volume of NaOH in the buret.


DataTrial 1 Trial 2 Trial 3

Mass KHP 0.433g 0.409g 0.406g

Moles KHP

Initial buret reading

1.42 mL 1.00 mL 1.25 mL

Final buret reading

19.40 mL 18.30 mL 18.45 mL

Volume NaOH used

Molarity NaOH

Average Molarity NaOH

Std. dev.

Percent relative std. dev.



Mass KHP 0.433g 0.409g 0.406g

Moles KHP


1.42 mL 1.00 mL 1.25 mL

Final buret reading

19.40 mL 18.30 mL 18.45 mL

Volume NaOH used

17.98mL 17.30mL 17.20mL

Molarity NaOH


Std. dev.



Data

KHPmolKHPg

KHPmolKHPg 00212.0

23.204

1433.0



Mass KHP 0.433g 0.409g 0.406g

Moles KHP 0.00212 mol 0.00200 mol 0.00199 mol


1.42 mL 1.00 mL 1.25 mL

Final buret reading

19.40 mL 18.30 mL 18.45 mL

Volume NaOH used

17.98mL 17.30mL 17.20mL

Molarity NaOH


Std. dev.



Data

KHPmolKHPg

KHPmolKHPg 00212.0

23.204

1433.0

NaOHmolKHPmol

NaOHmolKHPmol 00212.0

1

100212.0


Data

KHPmolKHPg

KHPmolKHPg 00212.0

23.204

1433.0

NaOHmolKHPmol

NaOHmolKHPmol 00212.0

1

100212.0

MsolutionNaOHL

NaOHmol

solutionNaOHL

NaOHmolMolarity 109.0

01798.0

00212.0



Mass KHP 0.433g 0.409g 0.406g



1.42 mL 1.00 mL 1.25 mL

Final buret reading

19.40 mL 18.30 mL 18.45 mL

Volume NaOH used

17.98mL 17.30mL 17.20mL

Molarity NaOH 0.109M 0.116M 0.116M


Std. dev.



Data

100

116.0

109.0116.0%

agreement


Data

%03.6

100116.0

109.0116.0%

agreement


Data

Trial 1 Trial 2 Trial 3 Trial 4

Mass KHP 0.433 0.409 0.406 0.449



1.42 mL 1.00 mL 1.25 mL 18.45 mL

Final buret reading

19.40 mL 18.30 mL 18.45 mL 37.30 mL

Volume NaOH used

17.98mL 17.30mL 17.20mL

Molarity NaOH 0.109M 0.116M 0.116M


Std. dev.



Data


Mass KHP 0.433g 0.409g 0.406g 0.449g

Moles KHP 0.00212 mol 0.00200 mol 0.00199 mol 0.00220


1.42 mL 1.00 mL 1.25 mL 18.45 mL

Final buret reading

19.40 mL 18.30 mL 18.45 mL 37.30 mL

Volume NaOH used

17.98mL 17.30mL 17.20mL 18.85mL

Molarity NaOH 0.109M 0.116M 0.116M 0.117M


Std. dev.



Data


Mass KHP 0.433g 0.409g 0.406g 0.449g

Moles KHP 0.00212 mol 0.00200 mol 0.00199 mol 0.00220


1.42 mL 1.00 mL 1.25 mL 18.45 mL

Final buret reading

19.40 mL 18.30 mL 18.45 mL 37.30 mL

Volume NaOH used

17.98mL 17.30mL 17.20mL 18.85mL

Molarity NaOH 0.109M 0.116M 0.116M 0.117M


0.116M

Std. dev.



Data

100

117.0

116.0117.0%

agreement


Data

%855.0

100117.0

116.0117.0%

agreement


Data

00071.013

001.00)0(

1DeviationStandard

222

1

2

n

xxn

ii


Data

%61.0

100116.0

00071.0

100DeviationStandard

Dev.Std. RelativePercent

x


IMPORTANT REMINDER

• Label NaOH bottle with your name, solution concentration and section number.

• Save the unused solution in a location identified by your laboratory instructor.



Safety

• The NaOH solutions are corrosive. If you get some on your skin, wash with water for at least five minutes. If any NaOH solution gets in the eyes IMMEDIATELY wash with water for at least fifteen minutes. Call for medical assistance!



Waste Disposal

All wastes from this experiment can be flushed down the drain with plenty of running water, except your unused NaOH.


Experiment 5 NaOH Standardization

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