Acids, Bases and Salts | Class 10 | Activity 2.6 with Solution

Activity 2.6  

• Take about 2 mL of dilute NaOH solution in a test tube and add two drops of phenolphthalein solution.
• What is the colour of the solution?

✅ Answer: The solution becomes pink colour.

• Add dilute HCl solution to the above solution drop by drop.
• Is there any colour change for the reaction mixture?

✅ Answer: The pink colour changes and disappears.

• Why did the colour of phenolphthalein change after the addition of an acid?

✅ Answer: Phenolphthalein is a weak acid. It gives pink colour in a strong base. When an acid is added, it reacts with the base and neutralisation reaction occurs. So pink colour disappears. 

• Now add a few drops of NaOH to the above mixture.
• Does the pink colour of phenolphthalein reappear?

✅ Answer: Yes.

• Why do you think this has happened?

✅ Answer: 

It is due to the increase in amount of base (NaOH) than acid.

The effect of a base is nullified by an acid and vice-versa.

NaOH(aq) + HCl(aq) → NaCl(aq) + H₂O(l)

• Activity 2.1
• Activity 2.2
• Activity 2.3
• Activity 2.4
• Activity 2.5
• Activity 2.6
• Activity 2.7
• Activity 2.8
• Activity 2.9
• Activity 2.10
• Activity 2.11
• Activity 2.12
• Activity 2.13
• Activity 2.14
• Activity 2.15

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