PH of solution and ph scale and measurement of PH

Ph Scale:

A number scale ranging from 0 to 14 that is used to describe the concentration of H+ ions in a solution is called pH scale.

Measurement of pH

Scientists usually use three methods to measure the pH of solution. These are:

1. Measurement of pH using paper or universal indicator.

2. Measurement of pH using Litmus paper

3. Measurement of pH using Acid-base indicator

1. Measurement of pH using paper or universal indicator.

PH paper or universal indicator paper is used to measure pH of a solution. For this purpose pH paper is dipped in the solution. The color that develops on the pH paper is compared to color of known pH on the chart. On chart, each color has a specific pH.

2. Measurement of pH using Litmus paper

One of the most commonly used methods in chemistry laboratory is the use of litmus paper. It is used to give a general indication of solution weather it is an acidic or basic. Litmus paper may be red or blue. An acid turns blue 💙 litmus into red. A base turns red litmus paper into blue.

3. Measurement of pH using Acid-base indicator

Acid Base indicators are also used to estimate the pH of solution. These indicators are intensly colored organic compounds. They change their colours with small change in pH and indicat the pH of solution by colour. For this purpose, we add few drops of an indicator to an aqueous solution of unknown pH and measure the pH of solution from resulting solution.

Question: What are applications of pH measurement in analytical chemistry?

Answer.

PH measurement has valuable applications. It helps analytical chemist to

I. To create soil conditions ideal for plants growth

ii. Medical diagnosis

iii. Maintaining the correct acid-base balance in swimming 🏊‍♂️ pool

iv. Electroplating

v. Manufacturing of medicines, tao water and waste 🗑 water

Self assessment Excercise

1. Write names of three acid-base indicators.

2. What is the colour of methyl red in solution of i. pH = 4, ii. pH = 9?

3. Bromothymol blue added to a solution imparts blue colour.

4. What is the pH of this solution? pH = 5 or 9

Answer.

1. Methyl red, bromothymol blue, phenolphthalein

2. i. Red ii. Yellow

3. i. Yellow ii. Blue

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