Standarization of NaOH Formal Report PDF

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1st formal report for chemistry 126 ...

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Standardization of NaOH INTRODUCTION

Neutralization is the process when an acid reacts with a base. The reaction happens instantaneously when they are mixed. The mix is hydronium ions with hydroxide ions(1). � #� %() +

+

(2 () → 2.()

(1)

This lab consists of finding the concentration of the reaction, but there is a sodium hydroxide instead of hydroxide. To determine the concentration, standardization has to be used to find the concentration of the solution. Standardizing the sodium hydroxide helps get an accurate and precise needed to get the concentration. For a salt like sodium hydroxide to be standardized it has to react with a very pure sample of potassium hydrogen phthalate, also known as KHP. When the solid KHP is dissolved in water and a base of sodium hydroxide is added by titration (2), the reaction will get to a point where its neutralized, that means that the reaction has met its end point. The end point of this reaction it very close to the equivalence point, which means the moles or acid with be the same as the moles of base. �� � 2�3�3()(+ () →

() +

.

2

�3�3() (2)

By recording the weight of the sample of KHP and the volume of base needed to neutralize it, the molarity of NaOH can be found. Once the concentration of NaOH is found, it will help to find the percent purity of an unknown KHP. The purpose of this lab is to accurately determine the concentration of a solution of sodium hydroxide against a very pure grade of KHP and determine the percent purity of an impure unknown KHP sample. EXPERIMENTAL

The experiment required a solution to be made to use as the base. It was made by adding 75mL of sodium hydroxide and approximately 675mL of DI water into a 1L Nalgene bottle. The solution that was made was then used as the base in both titrations. In part one of the experiment, 3 samples of pure KHP were obtained all weighing approximately 0.5g. Then the samples of KHP were put in separate 250mL Erlenmeyer flask, along with 100mL of DI water. All the flasks

were then warmed gently until the KHP was fully dissolved and then two drops of phenolphthalein were added. The buret cleaned and then filled with the sodium hydroxide and DI water solution. Then the buret was placed over an Erlenmeyer flask and was transferred into the flask by drops until the solution resulted in a faint pink. The procedure was repeated was then repeated two more times with the other sample. In part two of the experiment 3 samples of impure KHP were obtained all weighing approximately 0.7g. Then the samples were put in separate 250mL Erlenmeyer flask with 100mL DI water. Then they were gently warmed until all the impure KHP was dissolved. The buret was cleaned and then filled with the sodium hydroxide and DI water solution. Then the buret was placed over an Erlenmeyer flask and was transferred into the flask by drops until the solution resulted in a faint pink.Then the procedure of titration was repeated three times. DATA

The data from the first part of the lab can be found on table 1. The information collected was used to find the concentration of NaOH in a pure sample of KHP. To obtain the moles of KHP, the mass had to be multiplied by one mole over 204.3grams (3). Since it was a pure sample of KHP its number of moles is the same as NaOH. With knowing the moles of NaOH, the concentration can be found by diving the moles of NaOH by the liters of the NaOH used in the titration (4). � ���

= � ���

��

��� ×

=

>?@A

(3)

.B3..#D

][ =

>?@AG M,OGAP

?H Q?

IJKL (4) QRQSJQA

After the concentration of each trial was found the mean of the concentrations was found and it was 2.4. After finding the mean of the concentration, the standard deviation was found to be 0.4. Table 1: Standardization of Sodium Hydroxide Solution

Mass of Pure

Amount of NaOH

Moles of KHP

KHP

used in titration

(mol)

Concentration of NaOH in pure KHP (M)

(g)

(mL)

Trail 1

0.5244

33.4

0.078

2.3

Trial 2

0.5433

30.8

0.077

2.5

Trial 3

0.5083

31.8

0.075

2.4

In table 2, it’s the data collected from part 2 of the experiments. The mass and the amount of NaOH used were collected with the experiment. The percent KHP was calculated by the grams of KHP divided by the grams of the impure sample multiplied by 100(5). Before the percent could be calculated the moles of NaOH had to be found, they were found by multiplying the Molarity of NaOH by the liters of NaOH (6). The moles of NaOH are the same as the moles of KHP. Then the moles of KHP are converted to grams by multiplying the moles of KHP by 204.23g(7). % %= DSJ>G

?H

����� �� =

DSJ>GULV GJ>W@A

R>WOSA

× 100 (5)

=, × , � �� � (6) , �� � ��� ×

.B3

..#D

(7)

=

>?@A

Table 2: Analysis of Impure KHP

Mass of Impure

Amount of NaOH

KHP #104(g)

used in titration (mL)

Trial 1

0.7283

15.2

32.8

Trial 2

0.7348

15.4

32.5

Trial 3

0.7097

15.6

33.6

%KHP

Once the KHP percent were calculated, the mean of the percent was found,32.96%. With the mean the standard deviation of the percent was found to be 21.19%.

RESULTS/DISCUSSION

For the concentration of NaOH in a pure sample of KHP was found to be 2.39±0.4, with the concentration it was used to fins the percent purity of the unknown KHP sample. The impure sample came out to be 32.96%. There are many places for mistakes in this lab. The first one is if the buret wasn’t cleaned correctly with the base it could have residue from other chemicals that were in the buret and cause the concentration of the base to be wrong. Also, if measurements of volume used or the specific weight of the sample aren’t taken correctly the calculations won’t be precise. The results for the first part of the lab could be off because the buret wasn’t cleaned correctly.

CONCLUSION

This experiment taught the skill of how to perform a proper titration, and how salts act in an acid base reaction. The concertation of the pure KHP sample came out to be 2.4 and the percent purity of the impure KHP sample came out the be 32.96% pure. REFERENCES

Anliker, Breen ,Nyugen, Experimental Chemistry II Laboratory Manual 2007-2010 pp.47-52...