Grade 10 : Science - 2. Acids/Bases (Set 1) | Concept of Maths

Question 1

1. A solution $X$ has a hydrogen ion concentration of $10^{-4} \text{ mol/L}$. What is the pH of this solution and its nature?

A) pH = 10, Basic

B) pH = 4, Basic

C) pH = 4, Acidic

D) pH = -4, Acidic

Answer

Correct Answer: C

Solution: The pH of a solution is calculated using the formula: $$pH = -\log_{10}[H^+]$$ Given $[H^+] = 10^{-4}$, we have: $$pH = -\log_{10}(10^{-4}) = -(-4) = 4$$ Since the $pH < 7$, the solution is Acidic.

Question 2

2. When Zinc granules are treated with dilute sulfuric acid ($H_2SO_4$), which gas is evolved and how can it be tested?

A) Hydrogen gas; burns with a pop sound

B) Oxygen gas; rekindles a glowing splint

C) Carbon dioxide; turns lime water milky

D) Sulfur dioxide; has a pungent smell

Answer

Correct Answer: A

Solution: Metals react with dilute acids to produce hydrogen gas and a salt: $$Zn(s) + H_2SO_4(aq) \rightarrow ZnSO_4(aq) + H_2(g)$$ Hydrogen gas is colorless and odorless, and it burns with a characteristic pop sound when a burning candle is brought near the mouth of the test tube.

Question 3

3. An aqueous solution turns red litmus paper blue. The pH of this solution is likely to be:

A) 4

B) 10

C) 1

D) 5

Answer

Correct Answer: B

Solution: Bases turn red litmus blue. On the pH scale ($0$ to $14$), acidic solutions have pH $< 7$, neutral solutions have pH $= 7$, and basic solutions have pH $> 7$. Among the options, only 10 is greater than 7.

Question 4

4. Calcium phosphate is present in tooth enamel. Its nature is:

A) Acidic

B) Neutral

C) Amphoteric

D) Basic

Answer

Correct Answer: D

Solution: Calcium phosphate ($Ca_3(PO_4)_2$) is a salt of a strong base (Calcium hydroxide) and a weak acid (Phosphoric acid). Therefore, its nature is Basic. This is why tooth decay starts when the pH in the mouth falls below 5.5 (becoming more acidic).

Question 5

5. What is the chemical formula for Bleaching Powder?

A) $Ca(OH)_2$

B) $CaOCl_2$

C) $CaCl_2$

D) $CaCO_3$

Answer

Correct Answer: B

Solution: Bleaching powder is produced by the action of chlorine on dry slaked lime: $$Ca(OH)_2 + Cl_2 \rightarrow CaOCl_2 + H_2O$$ The chemical name is Calcium Oxychloride, and its formula is $CaOCl_2$.

Question 6

6. Which of the following is the correct reaction for the preparation of Baking Soda?

A) $NaCl + H_2O + CO_2 + NH_3 \rightarrow NH_4Cl + NaHCO_3$

B) $2NaCl + H_2O + CO_2 \rightarrow Na_2CO_3 + 2HCl$

C) $NaOH + CO_2 \rightarrow NaHCO_3$

D) $Na_2CO_3 + H_2O \rightarrow 2NaOH + CO_2$

Answer

Correct Answer: A

Solution: Baking soda (Sodium hydrogen carbonate) is produced using the Solvay process where Sodium Chloride reacts with water, carbon dioxide, and ammonia: $$NaCl + H_2O + CO_2 + NH_3 \rightarrow NH_4Cl + NaHCO_3$$

Question 7

7. If a solution $A$ has a pH of 2 and solution $B$ has a pH of 6, which solution has a higher concentration of $H^+$ ions and by what factor?

A) Solution B is $10^4$ times more acidic than A

B) Solution A is $4$ times more acidic than B

C) Solution A is $10^4$ times more acidic than B

D) Solution B is $4$ times more acidic than A

Answer

Correct Answer: C

Solution: We know $[H^+] = 10^{-pH}$. For solution A: $[H^+]_A = 10^{-2} \text{ mol/L}$ For solution B: $[H^+]_B = 10^{-6} \text{ mol/L}$ Ratio: $$\frac{[H^+]_A}{[H^+]_B} = \frac{10^{-2}}{10^{-6}} = 10^{-2 - (-6)} = 10^4 = 10,000$$ Thus, Solution A is $10,000$ (or $10^4$) times more acidic than Solution B.

Question 8

8. Which substance is used for softening hard water?

A) Baking Soda

B) Washing Soda

C) Bleaching Powder

D) Plaster of Paris

Answer

Correct Answer: B

Solution: Sodium carbonate ($Na_2CO_3 \cdot 10H_2O$), commonly known as Washing Soda, is used in glass, soap, and paper industries and is specifically used for removing permanent hardness of water.

Question 9

9. When Gypsum is heated to $373\text{ K}$, it loses water molecules and becomes:

A) Slaked Lime

B) Quick Lime

C) Anhydrous Calcium Sulfate

D) Plaster of Paris

Answer

Correct Answer: D

Solution: On heating Gypsum ($CaSO_4 \cdot 2H_2O$) at $373\text{ K}$ ($100^{\circ}\text{C}$), it loses water molecules to form Calcium Sulfate Hemihydrate ($CaSO_4 \cdot \frac{1}{2}H_2O$), which is Plaster of Paris.

Question 10

10. An ant's sting contains which acid that causes pain and irritation?

A) Methanoic Acid

B) Acetic Acid

C) Citric Acid

D) Tartaric Acid

Answer

Correct Answer: A

Solution: Ant stings and nettle stings inject Methanoic acid (also known as Formic acid) into the skin, causing a burning sensation. This can be neutralized by rubbing a mild base like baking soda.

Grade 10 : Science - 2. Acids/Bases (Set 1) | Concept of Maths