Standardization of Sodium Hydroxide Solution

This report is about how to standardize a Sodium Hydroxide (NaOH) solution by titrating it with pure sample of Potassium acid Phthalate (KHC8H4O4). This experiment has two sections. The first section is to standardize the Sodium Hydroxide by titration. Three sample of 0.7 – 0.9 g of solid KHP are place into each of the three numbered Erlenmeyer flasks. 50 ml of distilled water are added to each three of it from graduated cylinder and constantly shake it until the KHP solution are completely dissolve. 2 drops of phenolphthalein are add to each flask. Titrate each of the three flasks simultaneously with NaOH solution to the end point with the first appearance of a faint light pink that persist for 15 seconds. The colour will fade as CO2 from the air are dissolve in the solution. The second section is about standardization of diluted Sodium Hydroxide (NaOH). These sections are quite similar to section 1 but this method is titrating using a diluted Sodium Hydroxide which is diluted for 5 times. The rest of the experiment for section 2 is similar to section 1.

Objective:
* To standardize the sodium hydroxide solution with potassium hydrogen phthalate by using titration technique. * To calculate the concentration of the standard solution after titration is complete.

Materials:
100 mL Erlenmeyer Potassium Hydrogen Phthalate, KHP
50 mL Graduated cylinderDistilled Water
Titration Set Up Spatula
Burette Top loading balance ± 0.01g
50 % w/w NaOH

Procedure:
1. Standardization of sodium hydroxide (NaOH).
i. Three samples of solid KHP were weighed accurately of about 0.7 g to 0.9 g into each of the three clean, numbered Erlenmeyer flasks. ii. Each flasks were added 50 ml of distilled water from a graduated cylinder and the flask were shaken gently until the KHP is dissolved. Then 2 drops of phenolphthalein were added into each of the flask. iii. Each of them were titrated with the NaOH solution to the end point with the first appearance of a faint (light) pink color that persists for 15 second. The color faded as CO2 from the air dissolved in the solution. iv. The average molarity, the standard deviation and relative standard deviation (S/X) was calculated.

2. Standardization of Diluted NaOH
i. A diluted standardization NaOH were prepared in a 250 mL volumetric flask. ii. Three samples of solid KHP were weighed accurately of about 0.7 g to 0.9 g into each of the three clean, numbered Erlenmeyer flasks. iii. Each flasks were added 50 ml of distilled water from a graduated cylinder and the flask were shaken gently until the KHP is dissolved. Then 2 drops of phenolphthalein were added into each of the flask. iv. Each of them were titrated with the NaOH solution to the end point with the first appearance of a faint (light) pink color that persists for 15 second. The color faded as CO2 from the air dissolved in the solution. v. The average molarity, the standard deviation and relative standard deviation (S/X) was calculated.

Data.

1. Standardization of Sodium Hydroxide (NaOH) solution.
| Trial 1| Trial 2| Trial 3|
Mass of KHP (g)| 0.85| 0.80| 0.80|
Final burette reading, NaOH (ml)| 14.1| 26.80| 39.40| Initial Burette reading, NaOH (ml)| 0.0| 14.10| 26.80| Volume of NaOH (ml)| 50| 50| 50|
Molarity of NaOH (M)| 0.00028| 0.00031| 0.00031|
Average molarity of NaOH, (M)| 0.0003|
Standard deviation, σ| 1.732 x 10-5|

2. Diluted Standardization of Sodium Hydroxide (NaOH) solution. | Trial 1| Trial 2| Trial 3|
Mass of KHP (g)| 0.80| 0.80| 0.84|
Final burette reading, NaOH (ml)| 66.20| 128.30| 191.80| Initial Burette reading, NaOH (ml)| 0.00| 66.20| 128.30| Volume of NaOH (ml)| 66.20| 62.10| 63.50|
Molarity of NaOH (M)| 0.000059| 0.000063| 0.000062| Average molarity of NaOH, (M)| 0.000061|
Standard deviation, σ| 2.121×10-6|

Stoichiometry equation:KHP(acid)NaOH(base)
Acid + base salt + water KHC8H4O4 + NaOH NaKHC8H4O4 + H2O = mole ratio, 1:1

RAM of KHC8H4O4 = 39+1+ (12×8) + (1×4) + (16×4)
=204 g/mol
No of mole of KHP = 0.8 g204 g/mol
=0.00392 mol
Since the ratio KHP:Naoh = 1:1, the no of mole of NaOH = 0.00392 mol,
Molarity of NaOH = mol of NaOHvolume of NaOH
= 0.00392x where x is the volume of NaOH (refer to the table of result) DISCUSSION
In order to determine the concentration of a solution, there must be something to compare it against (benchmark). This benchmark is referred to as a standard. Sodium hydroxide (a base) is typically used as a standard to determine the concentration of acids. When an acid and base react, they form salt and water.

acid + base → salt + water
In a titration the volume of a solution added to a reaction is measured using a buret. A buret is a long tube with a valve (stopcock) at one end at one end that can be used to control the flow. Burets are typically calibrated in milliliters.

The acid and base are reacted together until one of the two is completely reacted. That point is called the endpoint that is neutral. If any additional acid or base is added, the solution will then become acidic or basic depending on which was added in excess. To visually determine the endpoint, an indicator is added to the reaction. An indicator is a chemical that changes colors at a particular pH. When just a tiny excess of the acid or base is added beyond the completion of the reaction, the indicator changes color. The amount added from the buret at this point is called the endpoint.

In order to use a standardized solution, the solution must be prepared. After preparation of the standard, the exact concentration of the standard solution must be determined. In this experiment, a sodium hydroxide solution (NaOH) will be prepared. In order to standardize the sodium hydroxide solution, there must be a substance used to standardize against. This substance will be potassium hydrogen phthalate (KHP). KHP is an organic acid that is solid and thus, easily weighed.

Using basic stoichiometry, the moles of NaOH in the solution can be determined from the moles of KHP added to the reaction.

Note the molar relationship. For every one mole of KHP, it would take one mole of NaOH to react it completely.
Since we weigh out a particular mass of KHP, we can easily calculate the moles of KHP we will use as the standard. The molecular mass of KHP is 204.2 amu.

Since for every one mole of KHP used it takes one mole of NaOH to react with it, if the moles of

KHP is known, the moles of NaOH is known.

moles of KHP = moles of NaOH
In the titration, the NaOH is added drop by drop using the buret. The buret indicates how much NaOH is being added to the KHP. At the point where all the KHP has been reacted (endpoint) any additional NaOH will turn the
solution basic. The indicator, phenolphthalein, turns the solution from clear to pink in a basic solution. This is called the endpoint.

The volume of NaOH added to the KHP is read off the buret in milliliters (endpoint) and converted to liters (liters = ml / 1000).

The concentration (molarity) of the sodium hydroxide solution can now be determined.

This standardized NaOH solution can now be used as a standard for the determination of acid concentrations.

Example:

0.8 grams of KHP is titrated with 40 ml of the unknown NaOH solution. What is the molarity of the

NaOH solution?

Solution:

Conclusion.
At the end of this experiment, student found that a diluted sodium hydroxide takes more time to standardize when titrating the solution (in present of light pale pink) compare to pure sample of sodium hydroxide solution. At the beginning of the experiment, students have theoretically predicted that diluted sodium hydroxide will take much longer time to standardize compare to pure sodium hydroxide. So the theory is acceptable. Student also learns how to properly standardize the sodium hydroxide whether it is pure sample or diluted solution and achieve the purpose of this experiment to standardize with potassium hydrogen phthalate by titration technique and to calculate the concentration of the standard solution after titration is complete. Next time to improve the data and the results of this experiment, student should carefully weigh the Potassium acid phthalate to the accurate measurement and patiently titrate the solution not to overdose.

Appendix.

1)
i. Titration can be defined as a procedure in which one solution is added to another solution until the chemical reaction between two solutes is complete. The concentration of one solution is known and that of the other solution is unknown.

ii. Titrant can be defined as a solution of known concentration which is added (titrate) to another solution to determine the concentration of a second chemical species.
2) 25.00 mL x 4.50 mol H2SO41000 mL soln x 2 mol NaOH1 mol H2SO4 x 1000 mL soln1.420 mol NaOH x 158 mL of 1.420M NaOH