Important Questions – Acids, Bases and Salts Class 10

📘 Important Questions – Acids, Bases and Salts

📚 Class 10 Science

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

   • Acids release $H^+$ ions (protons) only in the presence of water.

   • Without water, acids cannot ionize → no $H^+$ions → no acidic behaviour.

   2. What is the chemical name and formula of baking soda? Mention its one use.

   • Chemical name: Sodium hydrogen carbonate (or sodium bicarbonate).

   • Formula: $NaHCO_3$.

   • Use: It is used in making baking powder which helps cakes and bread to rise (as it releases $CO_2$ gas on heating).

   3. Why does dry HCl gas not change the colour of dry litmus paper, but wet HCl does?

   • Dry HCl has no $H^+$ ions because no water is present.

   • Wet HCl dissolves in water and forms $H^+$ ions → shows acidic character → changes blue litmus to red.

   
   

   4. How is plaster of Paris prepared? Write the balanced chemical equation.

   • Plaster of Paris is prepared by heating gypsum ($CaSO_4·2H_2O$) at 373 K.

   $$CaS{O}_4\cdot 2H_{2}O\stackrel{373K}{ \; \; \; \to }\mathrm{ \; \; C}aS{O}_4\cdot \frac{1}{2}{H}_{2}O+\frac{3}{2}{H}_{2}O$$

5. A solution turns red litmus blue. Its pH is likely to be: 6, 7, 8, or 4? Give reason.

• A solution that turns red litmus blue is basic.

• Among the options, pH 8 indicates a basic solution.
  ✅ Answer: pH = 8

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10 More Questions with Answers (Same Chapter)

Q6. Name one strong acid and one weak acid with examples.

• Strong acid: HCl (hydrochloric acid)

• Weak acid: CH₃COOH (acetic acid)

Q7. Which gas is usually liberated when an acid reacts with a metal? How can it be tested?

• Gas: Hydrogen ($H_2$)

• Test: Bring a burning matchstick near it → burns with a “pop” sound.

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Q8. What happens when zinc reacts with dilute sulphuric acid? Write the balanced equation.

$$Zn + H_2SO_4 \rightarrow ZnSO_4 + H_2 \uparrow$$

Q9. Name the acid present in the stomach. What is its function?

• Acid: Hydrochloric acid (HCl)

• Function: Helps in digestion by activating enzymes and killing bacteria.

Q10. Why are acids stored in glass bottles and not in metal containers?

• Acids corrode (react with) metals, but do not react with glass.

Q11. What is the chemical formula of bleaching powder? Mention one use.

• Formula: $CaOCl_2$

• Use: For disinfecting drinking water.

Q12. Write the reaction of a base with an acid (neutralization reaction) with example.

$$NaOH + HCl \rightarrow NaCl + H_2O$$

Q13. Why is common salt sometimes called “rock salt”?

• Because naturally occurring large crystals of salt are mined as “rock salt”.

Q14. What is the pH of pure water at room temperature?

• pH of pure water = 7 (neutral).

Q15. What is washing soda? Write its chemical formula and one use.

• Washing soda = Sodium carbonate decahydrate.

• Formula: $Na_2CO_3 \cdot 10H_2O$
  

• Use: Used in softening hard water.

Q16. Name the gas evolved when sodium hydrogen carbonate is heated. Write the reaction.

• Gas: Carbon dioxide ($CO_2$)

$$2NaHCO_3 \xrightarrow{\Delta} Na_2CO_3 + CO_2 + H_2O$$