NCERT Class X Science Solutions: Chapter 2 – Acids, Bases and Salts Part 2

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Question 6:

Compounds such as alcohols and glucose also contain hydrogen but are not categorized as acids. Describe an activity to prove it.

Answer:

Two nails are fitted on a cork and are kept it in a 100 mL beaker. The nails are then connected to the two terminals of a 6-volt battery through a bulb and a switch. Some dilute HCl is poured in the beaker and the current is switched on. The same experiment is then performed with glucose solution and alcohol solution.

Observations:

It will be observed that the bulb g lows in the HCl solution and does not g low in the glucose solution.

Compounds such as alcohols and glucose also contain hydrogen …

Categorized as Acids

Result:

HCl dissociates into H+ and Cl− ions. These ions conduct electricity in the solution resulting in the glowing of the bulb. On the other hand, the glucose solution does not dissociate into ions. Therefore, it does not conduct electricity.

Conclusion:

From this activity, it can be concluded that all acids contain hydrogen but not all compounds containing hydrogen are acids.

That is why, though alcohols and glucose contain hydrogen, they are not categorized as acids.

Question 7:

Why does distilled water not conduct electricity, whereas rain water does?

Answer:

Distilled water is a pure form of water and is devoid of any ionic species. Therefore, it does not conduct electricity. Rain water, being an impure form of water, contains many ionic species such as acids and therefore it conducts electricity.

Question 8:

Why do acids not show acidic behaviour in the absence of water?

Answer:

Acids do not show acidic behaviour in the absence of water because the dissociation of hydrogen ions from an acid occurs in the presence of water only. It is the hydrogen ions that are responsible for the acidic behaviour.

Question 9:

Five solutions A, B, C, D and E when tested with universal indicator showed pH as 4, 1, 11, 7 and 9, respectively. Which solution is?

  1. Neutral?

  2. Strongly acidic?

  3. Strongly alkaline?

  4. Weakly alkaline?

  5. Weakly acidic?

Arrange the pH in increasing order of hydrogen-ion concentration.

Answer:

  1. Neutral Solution D with pH 7

  2. Strongly alkaline Solution C with pH 11

  3. Strongly acidic Solution B with pH 1

  4. Weakly acidic Solution A with pH 4

  5. Weakly alkaline Solution E with pH 9

The pH can be arranged in the increasing order of the concentration of hydrogen ions as:

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