Exploring Acid-Base Equilibria: Standardization and Application of Titration Techniques

Acid base titration is all about achieving equilibrium between the moles of acid and moles of base. As a result, a salt is produced alone with water.

First of all, before performing any titration, conditioning of all the apparatus is required. Impurities might deflect the result. In the burette, previously prepared 0.1 M NaOH is filled. It is necessary to make sure that there are no bubbles at the end of the tip of the burette as it may make huge changes to the result.

NaOH with 0.1 M concentration is prepared by weighing 39.9971 gram NaOH on a weighing balance. Put this weighed NaOH into a volumetric cylinder of 1000 mL. Add 300 mL of water and then swirl till the NaOH is dissolved. At the end, make up the volume till the mark and 0.1 M NaOH solution is prepared. (Lot Number of NaOH- 185531). Three Erlenmeyer flask are taken and tared on a weighing balance. Around 0.400 gram of Potassium Hydrogen Phthalate (KHP) (Lot Number- 184621) is added into all the three flasks.

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Then, 100 mL deionized water is added to the flasks. It is added so that that KHP will dissolve. Five drops of 0.1 percent thymol blue is added to it. Indicator is added as it indicates the change in color of the solution at the end of the titration. The color change from colorless to permanent blue. Record the final volume reading on the burette.

Repeat this for three times with the other two flasks containing KHP. It is important to perform a titration for three times.

It provides precise results in comparison to performing it for only one time. According to the net volume of NaOH, Molarity of all the three trial was determined. The average value of the three trials for the standardization of NaOH is 0.1071 M NaOH.

The same NaOH solution with 0.1071 molarity will be used for titration of vinegar. In this experiment, vinegar of brand Heinz is used. The acid content on the label specified that it had 7 percent content.

For the titration of vinegar, the burette is conditioned for the contamination reasons. NaOH is filled in the burette and the initial reading of the burette is noted down. Three empty flasks are weighed and tared. Using a polyethylene pipette, 2.50 gram of vinegar is weighed in the previously weighed Erlenmeyer flasks. Thymol solution of 0.1 percentage concentration is used as an indicator. Five drops of thymol is added into the vinegar in the flasks. Each flask is titrated by NaOH. Presence of an indicator turns the color of the solution to blue from colorless when NaOH is added.

Using the data from the titration, the average mass percentage of the acetic acid in vinegar was determined to be 7.552 percent. It is 0.552 percentage more than the value on the label.

This is how concentration of an unknown compound can be determined using titration. Titration has many applications like: used in laboratory to identify the concentration of the medicine, in medical laboratories to find out the concentration of chemicals in urine or blood, in food industry to identify the vitamins’ concentration in food and many more. (Titration. (n.d.). Real World Application)

Acids can be defined as a substance or a compound produces a hydrogen ion [H+] when dissolved in water. Bases are the compounds that dissociates hydroxide ion [OH-] when dissolved in water. (Arrhenius. S, 1887). It can be described by the following example:

Acid: HCl = H+ + Cl-

Base: NaOH = Na+ + OH-

Another theory related to acid and base was proposed by J. N. Bronsted and T. M. Lowry. They proposed that acid is a substance that donated proton and base as a compound that accepts a proton (Bronsted. J and Lowry. T, 1923).

When an acid and a base are mixed together or reacted together, a neutral compound is formed. Water is also a product of each acid- base reaction. A neutral compound is formed when concentration of an acid and a base reach to an equilibrium.

Pure water is a neutral compound. The concentration of [H+] and [OH-] is equal (P. James, R. Roberts, Chemistry in the laboratory, Eighth Edition).

As it is difficult to measure the range of concentration, pH scale is developed. pH is a negative base 10 logarithm of the H+ ion. The equation can is as follows:

pH = -log [H+]

(S. Soren, 1909)

Concentration of acids and bases are differentiated according to the equation of pH. pH ranging from 0- 7 are considered as acids. The compounds which are possessing pH of 7 are the neutral compounds. Those compounds or substance which have pH ranging from 7- 14 are the basic compounds. (S. Soren P., 1909)

Figure 1 illustrates different compounds and their respective pH according to the concentration of hydrogen and hydroxide ion present in it.

Standardization is an analytical method where concentration of a solution is confirmed by comparing it to a standard solution. In the current experiment, standardization of NaOH is done to determine its accurate concentration before using it for titration ((P. James, R. Roberts, Chemistry in the laboratory, Eighth Edition)

Titration is a quantitative method to determine the concentration of an titrant using a solution of known concentration which is also known as an a titrate. The concentration of a solution can be determined when the equilibrium is achieved between the moles of titrant and a titrate. That equilibrium can be identified by the change is color of the solution as an indicator is added. Use of various glassware is done while performing a titration (Editors of Encyclopedia, October 6, 2017).

For the weal acids like acetic acids, which is used in the experiment performed:

Number of moles of acid = number of moles of base

Figure 2 describes the a usual arrangement of apparatus for titration where a burette is used with a stopcock and a Erlenmeyer flask with a solution of unknown concentration.