Question

Finding pH of the following samples by using pH paper/universal indicator:
a.) Dilute Hydrochloric Acid
b.) Dilute NaOH solution
c.) Dilute Ethanoic Acid solution
d.) Lemon juice
e.) Water

Answer 1

The nature of the chemicals used in laboratories is either basic, acidic or neutral. This characteristic depends on the ions they release. A chemical is said to be acidic if it releases H+ ions and basic if it releases OH– ions in its aqueous solutions.

Complete step by step answer:
- The pH is the measure of the acidic or basic power of a solution. It is a scale for measuring hydrogen ion concentration in a solution.
- The pH scale varies from 0 to 14. Neutral solution has a pH of 7.
- pH is defined as the negative logarithm of ${{H}^{+}}$ ions. It can be mathematically represented as
$pH=-{{\log }_{10}}[{{H}^{+}}]$

pH scale

- To find the pH of the given chemicals, the apparatus required is as follows:
Test tubes
Test tube stand
Dropper
Glass rod
pH paper strips
pH paper colour chart
- First of all, arrange all the chemicals in clean, dry test tubes on the test tube stand.
- Secondly, put one or two drops of each test solution on pH paper strips using a glass rod.
- We will compare the pH using the pH scale chart from the observations given below:

Sr. No.	Sample Solution	Colour appeared on pH paper	pH of the solution	Inference
1.	Dilute HCl	Red	1	Strong acid
2.	Dilute NaOH solution	Purple	14	Strong alkali
3.	Dilute Ethanoic Acid solution	Yellow	3	Weak acid
4.	Lemon Juice	Orange	2	Acid
5.	Water	Green	7	Weak alkali

Note: As pH depends upon ${{H}^{+}}$ concentration and in an aqueous solution ${{H}^{+}}$ and $O{{H}^{-}}$ ion concentrations are correlated, Therefore, every acidic and basic solution shows different colour at different pH .