Solution to Activity 2.2 of NCERT Class 10 Science Chapter 2 Acids, Bases and Salts

2. Complete Activity 2.2 (Page 18).

Take some finely chopped onions in a plastic bag along with some strips of clean cloth. Tie up the bag tightly and leave overnight in the fridge. The cloth strips can now be used to test for acids and bases.
Take two of these cloth strips and check their odour.
Keep them on a clean surface and put a few drops of dilute HCl solution on one strip and a few drops of dilute NaOH solution on the other.
Rinse both cloth strips with water and again check their odour.
Note your observations.
Now take some dilute vanilla essence and clove oil and check their odour.
Take some dilute HCl solution in one test tube and dilute NaOH solution in another. Add a few drops of dilute vanilla essence to both test tubes and shake well. Check the odour once again and record changes in odour, if any.
Similarly, test the change in the odour of clove oil with dilute HCl and dilute NaOH solutions and record your observations.

Answer:

Aim: To test the odour change of the cloth strips, vanilla essence and clove oil in contact withdilute HCl and dilute NaOH solutions and conclude based on that.

Materials Required: Finely chopped onions, plastic bag along, strips of clean cloth, SILUTE vanilla essence, clove oil, dilute HCl and dilute NaOH solutions.

Procedure:

(i) The finely chopped onion pieces and cloth strips are tied in the plastic bag and left overnight in the fridge.

(ii) Now two of the cloth strips are taken and their odour is checked.

(iii) They are kept on a clean surface and a few drops of dilute HCl solution is put on one strip and a few drops of dilute NaOH solution is put on the other.

(iv) The cloth strips are rinsed with water and their odour is checked again. The observations are noted.

(v) Then dilute vanilla essence and clove oil is taken and their odour is checked.

(vi) Some dilute HCl solution is taken in one test tube and dilute NaOH solution is taken in another.

(vii) A few drops of dilute vanilla essence are added to both test tubes and shaken well. Any changes in odour are recorded.

(viii) Similarly, the change in the odour of clove oil with dilute HCl and dilute NaOH solutions is recorded.

Observations:

The odour of the cloth strips remains unchanged in contact with HCl. The cloth strips become odourless in contact with NaOH.

The odour of the vanilla essence remains unchanged in contact with HCl. The odour vanishes in contact with NaOH.

The odour of clove oil remains unchanged in contact with HCl and the odour vanishes in contact with NaOH.

Conclusions:

Since vanilla, onion and clove do not change odour in contact with acids but becomes odourless in contact with bases, they can be used as olfactory indicators.

“2. Complete Activity 2.2 (Page 18).

Similarly, test the change in the odour of clove oil with dilute HCl and dilute NaOH solutions and record your observations.

Take some finely chopped onions in a plastic bag along with some strips of clean cloth. Tie up the bag tightly and leave overnight in the fridge. The cloth strips can now be used to test for acids and bases.

Take two of these cloth strips and check their odour.

Keep them on a clean surface and put a few drops of dilute HCl solution on one strip and a few drops of dilute NaOH solution on the other.

Rinse both cloth strips with water and again check their odour.

Note your observations.

Now take some dilute vanilla essence and clove oil and check their odour.

Take some dilute HCl solution in one test tube and dilute NaOH solution in another. Add a few drops of dilute vanilla essence to both test tubes and shake well. Check the odour once again and record changes in odour, if any.” – Solved.