Activity 2.6 Class 10 Science

This activity explains the reaction between acids and bases and the neutralisation reaction.

Neutralisation Reaction Experiment

 

Materials used in the activity

S.N.	Materials
1	Hydrochloric acid
2	Sodium hydroxide
3	Phenolphthalein
4	Test tubes
5	Dropper

Procedure

We take a test tube and pour about 2 mL dilute NaOH solution in it, and now add two drops of phenolphthalein solution.  We observe the change in colour of the solution.

 Now we add dilute HCI solution to the above solution(in the same test tube) drop by drop and again notice the change in  colour of the solution

After observing the change, we again add a few drops of NaOH to the above mixture.

Observation

 

On adding phenolphthalein to NaOH solution, the solution turns pink, but colour disappears on adding a few drops of HCI to it. When NaOH solution is added again to this test tube, the pink colour reappears.

Explanation

Phenolphthalein is a P^H indicator.  When it is added to sodium hydroxide solution (alkaline nature), it turns pink, and when HCl is added to this, a metallization reaction takes place so the pink colour disappears.

Conclusion

This experiment shows that the addition of HCI solution destroys the alkaline nature of NaOH. On the other hand, the addition of NaOH solution destroys the acidic nature of HCI, i.e., both NaOH and HCI appear to cancel the effect of each other.

Multiple Choice Questions

   1.   What is the initial colour of the solution when phenolphthalein is added to sodium hydroxide?

a) White

b). Red

c). Pink

d). Yellow

Correct answer – (c) Pink

   2.   What happens when dilute hydrochloric acid is added to the sodium hydroxide and phenolphthalein solution?

a) The solution turns red

b). The solution turns Black

c). The pink colour becomes darker

d). The pink colour disappears

Correct answer – (d) The pink colour disappears

  

   3.  Which chemical reaction takes place when HCl is added to sodium hydroxide solution?

a). Combination reaction

b). Displacement reaction

c). Neutralisation reaction

d). Decomposition reaction

correct answer – (c) Neutralisation reaction

Answer the following questions 

 Q1. What is a neutralisation reaction?

Ans. -The reaction between an acid and a base to give salt and water is known as a neutralisation reaction.

Q2. Write one chemical equation for the above reaction. 

Ans. -    NaOH + HCl → NaCl + H₂O

 

   3.  What will happen if we add phenolphthalein to hydrochloric acid?

Ans.-  When phenolphthalein is added to hydrochloric acid, phenolphthalein remains colourless.

  4.  What happens when you add phenolphthalein to sodium hydroxide?

Ans. – When phenolphthalein is added to sodium hydroxide(a base), phenolphthalein changes to a pink colour.

   5.  Which reaction takes place between a base and an acid?

Ans. – Neuterlisation reaction 

Related Topics -

1. Activity 2.7

2.  Activity 2.5

2. Solutions of Chapter 2 

3. MCQ Questions of Chapter 2

4. Extra Questions of Chapter 2