Chemistry Worksheets Class 10 on Chapter 2 Acids, Bases and Salts - Set 1

Here is the solution and explanation for each question from the Chemistry Worksheet:

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Q1. The property which is not shown by acids is:

* a.) they have a sour taste.
* b.) they feel soapy.
* c.) they turn litmus red.
* d.) their pH is less than 7.

Answer: b.) they feel soapy.

Explanation:
Acids have several characteristic properties:
* They taste sour (like lemon juice or vinegar).
* They turn blue litmus paper red.
* Their aqueous solutions have a pH less than 7.
* They react with bases to form salts and water.

The property of feeling "soapy" or slippery is characteristic of bases, not acids. For example, soap itself is basic, and solutions of sodium hydroxide (NaOH) feel slippery on the skin. Therefore, feeling soapy is NOT a property of acids.

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Q2. A solution reacts with zinc granules to give a gas which burns with a pop sound. The solution contains:

* a.) Mg(OH)₂
* b.) Na₂CO₃
* c.) NaCl
* d.) HCl

Answer: d.) HCl

Explanation:
When zinc (Zn), a reactive metal, reacts with an acid, it produces hydrogen gas (H₂). The chemical reaction is:
`Zn + 2HCl → ZnCl₂ + H₂`

Hydrogen gas is highly flammable and burns with a distinctive "pop" sound when ignited. This is a standard test for hydrogen gas.

Let's check the other options:
* Mg(OH)₂ (Magnesium hydroxide): This is a base. It does not react with zinc to produce hydrogen gas.
* Na₂CO₃ (Sodium carbonate): This is a salt (of a weak acid and strong base). It reacts with acids to produce CO₂ gas, not H₂. CO₂ does not burn with a pop sound; it extinguishes flames.
* NaCl (Sodium chloride): This is a neutral salt. It does not react with zinc to produce any gas.

Only HCl (hydrochloric acid), being an acid, will react with zinc to produce hydrogen gas that burns with a pop sound.

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Q3. A solution turns red litmus blue. Its pH is likely to be:

* a.) 1
* b.) 4
* c.) 5
* d.) 10

Answer: d.) 10

Explanation:
Litmus paper is an indicator:
* Red litmus turns blue in the presence of a base.
* Blue litmus turns red in the presence of an acid.

Since the solution turns red litmus blue, it is basic. Basic solutions have a pH greater than 7.

Looking at the options:
* pH 1, 4, and 5 are all acidic (pH < 7).
* pH 10 is basic (pH > 7).

Therefore, the pH is likely to be 10.

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Q4. Which of the following salts does not contain water of crystallisation?

* a.) Blue vitriol
* b.) Baking soda
* c.) Washing soda
* d.) Gypsum

Answer: b.) Baking soda

Explanation:
Water of crystallisation refers to water molecules that are chemically bound within the crystal structure of a salt. Salts containing this are called hydrates.

Let's examine each option:
* Blue vitriol: This is copper(II) sulfate pentahydrate, CuSO₄·5H₂O. It clearly contains 5 molecules of water of crystallisation.
* Baking soda: This is sodium bicarbonate, NaHCO₃. It is an anhydrous salt, meaning it does *not* contain water of crystallisation in its normal solid form.
* Washing soda: This is sodium carbonate decahydrate, Na₂CO₃·10H₂O. It contains 10 molecules of water of crystallisation.
* Gypsum: This is calcium sulfate dihydrate, CaSO₄·2H₂O. It contains 2 molecules of water of crystallisation.

Therefore, baking soda (NaHCO₃) is the only one listed that does not contain water of crystallisation.

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Q5. Bases generate ___ ions in water.

* a.) H⁻
* b.) H⁺
* c.) OH⁻
* d.) OH⁺

Answer: c.) OH⁻

Explanation:
According to the Arrhenius definition of bases, a base is a substance that, when dissolved in water, increases the concentration of hydroxide ions (OH⁻).

For example:
* NaOH → Na⁺ + OH⁻
* Ca(OH)₂ → Ca²⁺ + 2OH⁻

Acids, on the other hand, generate H⁺ (or H₃O⁺) ions in water.

The other options are incorrect:
* H⁻ is the hydride ion, not produced by typical bases in water.
* H⁺ is produced by acids.
* OH⁺ is not a stable ion under normal aqueous conditions.

So, bases generate OH⁻ ions.

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Q6. What is the role of tartaric acid in baking powder?

Answer:
Tartaric acid in baking powder acts as an acid component that reacts with the base (usually sodium bicarbonate, NaHCO₃) when mixed with water. This reaction produces carbon dioxide (CO₂) gas, which gets trapped in the dough or batter, causing it to rise and become light and fluffy during baking.

Chemical Reaction:
`NaHCO₃ + H⁺ (from tartaric acid) → CO₂↑ + H₂O + Salt`

Without the acid, the sodium bicarbonate would not decompose to release CO₂ gas at room temperature or during baking. Tartaric acid provides the necessary H⁺ ions for this reaction. Sometimes, cream of tartar (potassium bitartrate) is used instead of tartaric acid for the same purpose.

In summary, tartaric acid ensures the production of carbon dioxide gas, which is essential for leavening (rising) baked goods.