Saturday, September 17, 2022

How to prepare KCl solution for conductivity

Learn how to make potassium chloride solution for calibration of conductivity meter which is needed in many applications such as research, practical, pharmaceutical, chemical laboratory, industries, etc.

The conductivity meter is a very significant tool in several applications for measuring conductance, it measures the level of conductivity in solutions. To provide reliable readings, the conductivity cell must be in proper working condition.

A few factors that could shorten the lifespan of the conductivity cell include sample composition, temperature, and how the conductivity cell is stored and maintained. Care and preservation of conductivity cells ensure not just a longer lifespan but also more precise readings.

Requirements of glassware, chemicals, and apparatus:
Digital balance, beaker, pipette, pipette bulb, volumetric flask, measuring cylinder, glass rod, funnel, distilled water, AR/LR grade potassium chloride (KCl), etc.

How to prepare calibration solution for conductivity meter:

Calculation method:

Molar mass KCl = 39.1+35.45 = 74.55 g/mol,

Mol KCl needed to make 100 mL of 0.01 M solution:

mol = 100 mL / 1000 mL/L x 0.1 mol /L = 0.01 mol KCl

Mass KCl required = 0.01 mol * 74.55 g/mol = 0.7456 g KCl

Therefore, to make a standard KCl solution for conductivity (0.01 M KCl, 1411 μS at 25°C), weigh accurately 0.7456 gm of potassium chloride and dissolve it in 500 ml of distilled water in a volumetric flask. Once it has completely dissolved, make up the volume to 01 liter with distilled water, and properly mix it.

The standard value of conductance at coefficient-1.92, K=cell constant:

Molarity/Concentration of KCl

Standard conductivity

0.001 M

147 µS/cm ±10% at 25°C

0.01 M

1.413 mS/cm ±10% at 25°C

0.1 M

12.88 mS/cm ±10% at 25°C

Why do we use KCl for calibration of the conductivity meter?

The conductivity meter should be frequently calibrated using pre-prepared standard solutions to get accurate and reproducible results. Potassium chloride (KCl) is the most common solution to perform the calibration of the conductivity meter because it is soluble and very stable.
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Tuesday, September 6, 2022

Why KCl is used in pH meter

The basic parts of a pH meter are the glass electrode, reference electrode, electrolyte solution, temperature sensor, etc. It is the most commonly used instrument in our lab for research, industrial or practical purposes.

To obtain accurate results, it is necessary to calibrate the device regularly and keep the pH electrode moist. Therefore a manufacturer advises storing the pH electrode in 4M KCl or pH 04 solutions and it does not require storing in distilled or deionized water.

Why KCl solution used in pH meter?

To understand the reason for the use of KCl as an electrolyte, it is required to know the role of the electrolytic solution in a pH meter. The pH meter operates by immersing a glass electrode and a reference electrode in an electrolytic solution, which is then connected to the test solution via a porous ceramic membrane. The voltage is then displayed on a voltmeter which provides a pH reading.

Therefore, we need a solution in an electrolytic solution that contains enough ions to complete the circuit and does not change the pH of the test solution, as it is in a way, connected to it.

For this reason, we use a solution of KCl because it contains a good source of ions in the form of chlorine (Cl) ions. Furthermore, because KCl is neutral, it does not affect or change the pH of the test solution. Because of these two factors, potassium chloride (KCl) is what is used in pH meters.

Why electrodes are only put in a KCl solution?

Potassium chloride (KCl) and sodium chloride (NaCl) are typical electrolytes in a salt bridge. Potassium chloride is preferred over NaCl because of its greater mobility of K+ ions. Transport number shows which ion would move faster than the other. As a result, KCl gives the electrolyte used in salt bridges the least chance of ionic imbalance, or the least chance of retardation.

Why is a calomel electrode kept in a KCl solution?

Because the calomel electrode is made of 1M KCl or a saturated KCl solution, maintaining the electrode in the KCl solution helps prevent the electrolyte to come out or change the concentration of the cell.

Why is the top layer of a calomel electrode filled with saturated KCl?

In the calomel electrode, KCl acts as a salt bridge. Electrolytes that have anion and cation mobility that is equal, or substantially equal, are used as salt bridges.



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Saturday, September 3, 2022

How to prepare saturated KCL solution

Potassium chloride, also known as KCl or potassium salt, is a 1:1 mixture of potassium and chlorine ions in a metal halide salt. It looks like a white or colorless and odorless vitreous crystal.

The molecular weight of KCl is 74.555 g/mol−1, its density is 1.984 g/cm3, and it is soluble in water, highly soluble in alcohols, and insoluble in ether.

Requirements of glassware, chemicals, and apparatus:
Beaker, volumetric flask, glass rod, funnel, distilled water, AR/LR grade potassium chloride (KCl), spatula, etc.

How to prepare saturated solution of KCl

Using KCl and water, you can make a supersaturated solution by the following procedure:
  • Take a 250 ml beaker; add 100 ml of distilled water to it, then add KCl and mix well to dissolve.
  • Once it has completely dissolved, add more salt to the mixture and keep stirring.
  • At a temperature of 20°C, it can be noticed that 35.00 g of potassium chloride can be completely dissolved, and the solution becomes saturated.
  • If we increase the temperature, more amount of the solute will be able to dissolve in the solution.
  • If we increase the temperature of the solution to 80 °C the excess solute separates out in the form of crystals.

What is the concentration of saturated KCl?

The temperature-dependent solubility of saturated KCl determines its concentration.
  • KCl solubility at 20°C: 0,340 g.cm-3 in water = 340 g/l = 4.56 mol/l (Saturated KCl at 20°C)
  • KCl solubility at 30°C: 0,374 g.cm-3 in water = 374 g/l = 5.02 mol/l (Saturated KCl at 30°C)

How to store saturated KCl solution?

The saturated and supersaturated KCl solutions must be kept at room temperature in a closed container. There is no need to be concerned about the growth of microorganisms in the solution as it has a very high osmotic pressure.


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