Extra 30 short-answer questions from Chapter:2 Acids, Bases, and Salts for Class 10 CBSE Science:
What are acids? Give two examples.
Answer: Acids are substances that release H⁺ ions in aqueous solutions.
Example: Hydrochloric acid (HCl), Sulfuric acid (H₂SO₄)
What are bases? Give two examples.
Answer: Bases are substances that release OH⁻ ions in aqueous solutions.
Example: Sodium hydroxide (NaOH), Calcium hydroxide (Ca(OH)₂)
What is an alkali? Give an example.
Answer: An alkali is a water-soluble base.
Example: Potassium hydroxide (KOH)
Define the pH scale.
Answer: The pH scale measures the acidity or basicity of a solution on a scale of 0-14.
Acidic: pH < 7
Neutral: pH = 7
Basic: pH > 7
What happens to the pH of an acid when diluted?
Answer: The pH increases as the concentration of H⁺ ions decreases due to dilution.
What is the colour of litmus in acidic and basic solutions?
Answer:
Acidic solution: Blue litmus turns red
Basic solution: Red litmus turns blue
What is the colour of phenolphthalein in acids and bases?
Answer:
Acids: Colourless
Bases: Pink
What is the role of acids in our stomach?
Answer: The stomach secretes HCl to:
Kill bacteria
Aid digestion by breaking down food
Which acid is present in: (a) Vinegar (b) Lemon juice?
Answer:
(a) Acetic acid (CH₃COOH)
(b) Citric acid (C₆H₈O₇)
Which base is used in antacids? Why?
Answer: Magnesium hydroxide (Mg(OH)₂) is used in antacids to neutralize excess stomach acid.
What happens when an acid reacts with a metal? Give an example.
Answer: Acids react with metals to form salt and hydrogen gas.
Example: Zn+2HCl→ZnCl2+H2↑
What happens when acids react with metal carbonates?
Answer: Acids react with metal carbonates to produce salt, water, and CO₂ gas.
Example: Na2CO3+2HCl→2NaCl+H2O+CO2↑
What happens when acids react with bases? Name the reaction.
Answer: Acids react with bases to form salt and water. This is called a neutralization reaction.
Example: NaOH+HCl→NaCl+H2O
What is the reaction between quicklime and water? Why is it exothermic?
Answer:
Reaction: CaO+H2O→Ca(OH)2+Heat
It is exothermic because heat is released.
How do metal oxides react with acids? Give an example.
Answer: Metal oxides react with acids to form salt and water.
Example: CuO+2HCl→CuCl2+H2O
How do non-metal oxides react with water? Give an example.
Answer: Non-metal oxides react with water to form acids.
Example: CO2+H2O→H2CO3CO_2 + H_2O → H_2CO_3CO2+H2O→H2CO3
What happens when ammonia dissolves in water?
Answer:
Reaction: NH3+H2O→NH4OH
Forms ammonium hydroxide, a weak base.
Write the reaction of hydrochloric acid with sodium bicarbonate.
Answer:
Reaction: NaHCO3+HCl→NaCl+CO2+H2O
How is a salt formed? Give an example.
Answer: Salts are formed by the neutralization of acids and bases.
Example: NaOH+HCl→NaCl+H2O
Why do acids conduct electricity?
Answer: Acids release H⁺ ions in water, which help in the conduction of electricity.
What is the pH of pure water? Why?
Answer: The pH of pure water is 7 because it is neutral.
What is the chemical formula of baking soda? What is its use?
Answer: Formula: NaHCO₃
Used in baking, antacids, and fire extinguishers.
What is washing soda? Write its formula.
Answer: Washing soda is sodium carbonate decahydrate.
Formula: Na₂CO₃·10H₂O
What is Plaster of Paris? Write its formula.
Answer: Plaster of Paris is calcium sulphate hemihydrate.
Formula: CaSO₄·½H₂O
What happens when an acidic solution is mixed with a basic solution?
Answer: They undergo a neutralization reaction forming salt and water.
What is the chemical name of slaked lime? Write its formula.
Answer: Chemical name: Calcium hydroxide
Formula: Ca(OH)₂
What happens when excess CO₂ is passed through lime water?
Answer: Lime water turns milky due to the formation of CaCO₃.
Reaction: Ca(OH)2+CO2→CaCO3+H2O
Why does tooth enamel decay in the presence of acids?
Answer: Acids produced by bacteria in the mouth react with calcium phosphate (tooth enamel), leading to decay.
What is the effect of acid rain on buildings?
Answer: Acid rain reacts with limestone (CaCO₃) in buildings, causing damage.
Reaction: CaCO3+H2SO4→CaSO4+CO2+H2O
How does pH affect plant growth?
Answer:
Plants grow best in neutral/slightly acidic soil (pH 6-7).
Too much acidity or alkalinity damages roots and affects growth.
