Chrominfo: Conductometric titration of strong acid and weak acid against a strong base

Learn about the conductometric titration of strong acid and weak acid against a strong base through a laboratory experiment or practical.

Aim:

To determine the strength of a mixture of strong acid and weak acid using a strong base by conductometry.

Requirements:

Glasswares: Burette, burette stand, conical flask, volumetric pipette, beaker, volumetric flask, funnel, glass rod, and wash bottle, etc.

Chemicals: LR grade acetic acid, sodium hydroxide (NaOH), hydrochloric acid (HCl), potassium hydrogen phthalate (KHP), and phenolphthalein indicator, etc.

Apparatus: Digital/analytical balance, and ultrasonicator, conductometer, and magnetic stirrer.

Principle:

A mixture of acids directly titrates with NaOH to determine its strength, in which hydrochloric acid is a strong acid, acetic acid is a weak acid, and sodium hydroxide is a strong base.

The conductometric titration principle is based on the fact that throughout the titration, one of the ions is replaced by the other, and these two ions usually have different ionic conductivities, causing the conductivity of the solution to change.

Conductometric titration of strong acid and weak acid against a strong base

Preparation of reagents and solutions:

Preparation of 1 M hydrochloric acid solution:

Click here to get the procedure of preparation of 1 M hydrochloric acid solution.

Preparation and standardization of 1 M NaOH solution:

Click here to get the procedure of preparation and standardization of 1 M sodium hydroxide solution.

Titration procedure:

All glassware should be cleaned and dried according to standard laboratory procedures.
Before filling the burette for the titration, rinse it with distilled water and then pre-rinse it with a portion of the titrant solution. Pre-rinsing is required to make sure that all solution in the burette is the desired solution, not a contaminated or diluted solution.
Take the unknown stock solution of titrant in a clean and dry beaker then fill the burette using the funnel.
Remove air bubbles from the burette and adjust the reading to zero.
Switch ON the instrument and calibrate the conductivity meter with a standard solution.
(Because potassium chloride (KCl) is soluble and stable, it is the most commonly used calibration solution for conductivity meters)
Once it is calibrated, rinse the platinum electrode with distilled water.
Take 75.00 ml of HCl, 25.00 ml of acetic acid, and pour it into a beaker.
Properly place the beaker on a stirrer and immerse both the platinum electrodes and set the burette properly on the beaker.
Note down the initial reading (conductance) of the sample i.e. millisiemens (mS) or micro-siemens (µS).
Turn on the stirrer and add 01.00 ml standardized NaOH solution from the burette at a time, properly record the readings.
Continue the titration process until the endpoint is reached.
The actual endpoint of the titration is indicated by a sharp increase in the conductivity of the sample.
Even after you've reached the endpoint, take a few more readings.
Plot the graph between conductivity (mho) vs volume of NaOH and calculate the strength of the sample mixture.