Class 10th Science Acids bases and Salts NCERT Solution CBSE 2023 - Free Printable

Let’s go through each question one by one, step by step, so you understand why the answers are what they are.

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Question 1: Why do HCl, HNO₃, etc., show acidic characters in aqueous solutions while solutions of compounds like alcohol and glucose do not show acidic character?

Step-by-step thinking:

- Acids like HCl (hydrochloric acid) and HNO₃ (nitric acid) break apart in water to give hydrogen ions (H⁺).
- These H⁺ ions don’t stay alone — they join with water molecules (H₂O) to form hydronium ions (H₃O⁺). That’s what makes the solution acidic.
- Example reaction:
HCl → H⁺ + Cl
Then: H⁺ + H₂O → H₃O⁺

- Now, alcohol and glucose also have hydrogen atoms in them — but those hydrogens are stuck tightly inside their molecules. They don’t break off as H⁺ ions when dissolved in water.
- No H⁺ ions = no acidity.

So, it’s not about having hydrogen — it’s about whether that hydrogen can become free H⁺ ions in water.

✔ Final Answer for Q1:
HCl and HNO₃ release H⁺ ions in water, which form H₃O⁺ and make the solution acidic. Alcohol and glucose contain hydrogen but cannot release H⁺ ions in water, so they don’t act as acids.

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Question 2: Why does an aqueous solution of an acid conduct electricity?

Step-by-step thinking:

- Electricity needs charged particles (ions) to move through a liquid to carry the current.
- When acids dissolve in water, they split into positive ions (like H⁺ or HO⁺) and negative ions (like Cl⁻ or NO⁻).
- These ions are free to move around in the solution.
- So, when you put electrodes in the solution, the ions move toward opposite charges — allowing electricity to flow.

✔ Final Answer for Q2:
Acid solutions conduct electricity because they produce moving ions (charged particles) when dissolved in water.

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Question 3: Why does dry HCl gas not change the colour of the dry litmus paper?

Step-by-step thinking:

- Litmus paper changes color only when it comes in contact with H⁺ ions (which come from acids in water).
- Dry HCl gas is just HCl molecules floating in air — no water, so no dissociation into H⁺ and Cl.
- Also, if the litmus paper is dry, there’s no water to help HCl turn into ions even if it touches the paper.
- So, no H⁺ ions → no color change.

✔ Final Answer for Q3:
Dry HCl gas doesn’t produce H⁺ ions without water, and dry litmus paper has no water to help form those ions — so no color change happens.

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Question 4: While diluting an acid, why is it recommended that the acid should be added to water and not water to the acid?

Step-by-step thinking:

- Mixing acid and water releases heat — it’s an exothermic process.
- If you add water to concentrated acid, the small amount of water can get very hot very fast — maybe even boil suddenly and splash out dangerous acid!
- But if you slowly add acid to a large amount of water, the heat spreads out safely in the bigger volume of water.
- It’s like pouring syrup into milk vs. pouring milk into syrup — one mixes smoothly, the other might splatter.

✔ Final Answer for Q4:
Adding acid to water lets the heat spread safely in the larger amount of water. Adding water to acid can cause sudden boiling and splashing of hot acid — which is dangerous.

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Final Answer:
Q1: HCl and HNO₃ release H⁺ ions in water to form H₃O⁺, making them acidic; alcohol and glucose cannot release H⁺ ions, so they aren’t acidic.
Q2: Acid solutions conduct electricity because they contain mobile ions that carry electric current.
Q3: Dry HCl gas doesn’t produce H⁺ ions without water, and dry litmus paper lacks water to allow ion formation — so no color change occurs.
Q4: Always add acid to water (not water to acid) to prevent dangerous splashing caused by rapid heat release during mixing.