Question

Acid-Base Titrations.

Answer 1

Types of acid-base titrations 

1. Strong acid vs. strong base (HCl vs. NaOH) 

2. Weak acid vs. strong base (CH₃COOH vs. NaOH) 

3. Strong acid vs. weak base (HCl vs. NH₄OH) 

• Indicator- Substance which is usually added into the solution taken in the titration flask to detect the equivalence/end point. 

• Indicators which are used in the acid-base titrations are known as pH indicators or neutralisation indicators. 

• An acid-base indicator is a weak organic acid (e.g., phenolphthalein) or weak organic base (e.g., methyl orange). 

• They possess different colour in the acidic and basic medium which indicate the end point in the titration.

• Some commonly used indicators with their pH range are as follows:

		Colour change
Indicator	pH range	Acidic Medium	Basic Medium
Methyl Orange	3.2-4.4	Red	Yellow
Methyl red	4.8-6.0	Red	Yellow
Phenolphthalein	8.2-10.0	Colourless	Pink
Thymol blue	8.0-9.6	Yellow	blue

Phenolphthalein

It is a weak organic acid (HPh).

Methyl Orange, (MeOH)

It is a weak base.