Activity 2.1 Class 10 Science

Aim of the activity

To test the acid bases using different indicators and record the observation to understand the acidic and basic nature.

 

Material used in the activity

1. Samples of acids and bases

1. Hydrochloric acid (HCl)
2. Sulphuric acid (H2SO4)
3. Nitric acid (HNO)3
4. Acetic acid (CH3COOH)
5. Sodium hydroxide (NaOH)
6. Calcium hydroxide [Ca(OH)2]
7. Potassium   hydroxide (KOH)
8. Magnesium  hydroxide [Mg(OH)2]
9. Ammonium  hydroxide (NH4OH)

  2. Test tubes

  3. Watch glass

  4.Indicators

1. Blue litmus solution
2. Red litmus solution
3. Phenolphthalein solution
4. Methyl orange solution

Procedure

We collect the above samples form the science laboratory in test tube. At first put a drop of the above solutions on watch glass separately. Now tests these samples with given indicators one by one

1. We put a few drops of blue litmus solution in each watch glass and observe the change in colour.

 

2. Now put a few drops of red litmus solution in each watch glass and notice the change in colour

 

3.Now add a few drops of phenolphthalein solution and see the change in colour of each given sample

 

4.We add methyl orange solution in each watch glass and observe the change in the colour.

 

Note :-  Take fresh solution of samples in watch glasses each time

Now we note down observation in the given table

 

Observation

The following table show the change in colour with different indicators.

Sample solution	Blue litmus solution	Red litmus solution	Phenolphthalein solution	Methyl orange solution
HCI,	Red	No change	Colourless	Red
HNO3	Red	No change	Colourless	Red
H2SO4	Red	No change	Colourless	Red
CH3COOH	Red	No change	Colourless	Pink
NaOH	No change	Blue	Pink	Yellow
KOH	No change	Blue	Pink	Yellow
Ca(OH)2	No change	Blue	Pink	Yellow
Mg(OH)2	No change	Blue	Pink	Yellow
NH4OH	No change	Blue	Pink	Yellow

 

Explanation

Each indicators (used in this activity) has its PH range and  reacts with H+ ions and OH- ions in different ways so they show different type of colour changes in acidic and basic solutions.

Acids turns blue litmus into red and do not change the colour with red litmus solution. phenolphthalein remains colourless and methyl orange turns red or pink in acidic solutions.

Bases turn red litmus blue but do not change colour with blue litmus. Phenolphthalein turns pink and methyl orange turns yellow in basic solutions.

Conclusion

These indicators tell us whether a substance is acidic or basic by changing  colour.

So on the basis of above table, we can easily conclude that HCl,H2SO4,HNO3 and CH3COOH are acids and NaOH, KOH, Mg(OH)2, Ca(OH)2 and NH4OH are bases.

FAQs

1.Why does phenolphthalein turn pink in basic solution?

Ans. – Phenolphthalein changes colour at a PH above 8.3 and the given basic solution has PH above 7. So it changes colour in basic solutions.

2.What is chemical name of NaOH?

Ans.- Sodium hydroxide

3.Phenolphthalein is added to solution ‘X’, if there is no change in colour, then what is the nature of solution ‘X’?

Ans-  Solution ‘X’ is acidic in nature.

4.What is the nature of sodium hydroxide?

Ans.-  Sodium hydroxide is basic or alkaline in nature.

5.Which solutions remained colorless with phenolphthalein?

Ans.-  Acidic solutions