Acids, Bases and Salts — Previous Year Questions (Class 10 Science)
This chapter covers properties of acids and bases, pH scale, neutralization reactions, and salt formation. Understanding these concepts is fundamental to c
TL;DR: This chapter covers properties of acids and bases, pH scale, neutralization reactions, and salt formation. Understanding these concepts is fundamental…
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This chapter covers properties of acids and bases, pH scale, neutralization reactions, and salt formation. Understanding these concepts is fundamental to c
Acids, Bases and Salts — Previous Year Questions with Solutions
Q (2023, 2 marks): Define an acid and a base according to Arrhenius theory. Give one example each.
Answer: Acid (Arrhenius): A substance that produces H+ ions (hydrogen ions) when dissolved in water.
Example: HCl (Hydrochloric acid) → H+ + Cl-
Base (Arrhenius): A substance that produces OH- ions (hydroxide ions) when dissolved in water.
Example: NaOH (Sodium hydroxide) → Na+ + OH-
Q (2022, 2 marks): What is the pH scale? Name one substance each with pH < 7 and pH > 7.
Answer: pH scale is used to measure the acidity or basicity of a solution. It ranges from 0 to 14.
At pH = 7: neutral (pure water)
pH < 7: acidic
pH > 7: basic
Example of acidic substance (pH < 7): Lemon juice (pH ≈ 2)
Example of basic substance (pH > 7): Baking soda solution (pH ≈ 8)
Q (2023, 1 mark): Write the chemical equation for neutralization of HCl with NaOH to form salt and water.
Answer: HCl + NaOH → NaCl + H2O
or in ionic form:
H+ + OH- → H2O
This is an exothermic neutralization reaction.
Q (2021, 2 marks): What happens when sodium carbonate is treated with dilute hydrochloric acid? Write equation.
Answer: When sodium carbonate reacts with dilute HCl, salt (sodium chloride), water, and carbon dioxide gas are produced.
Na2CO3 + 2HCl → 2NaCl + H2O + CO2↑
The gas evolved can be tested with lime water, which becomes milky.
Q (2022, 3 marks): Classify the following as acidic, basic, or neutral salts: NaCl, KNO3, Na2CO3, NH4Cl.
Answer: NaCl (Sodium chloride): Neutral salt (formed from strong acid HCl and strong base NaOH)
KNO3 (Potassium nitrate): Neutral salt (formed from strong acid HNO3 and strong base KOH)
Na2CO3 (Sodium carbonate): Basic salt (formed from weak acid H2CO3 and strong base NaOH. CO3^2- undergoes hydrolysis, producing OH-)
NH4Cl (Ammonium chloride): Acidic salt (formed from strong acid HCl and weak base NH3. NH4+ undergoes hydrolysis, producing H+)
Q (2023, 2 marks): How is bleaching powder prepared? Write the chemical equation.
Answer: Bleaching powder is prepared by the action of chlorine gas on dry slaked lime (calcium hydroxide).
2Ca(OH)2 + 2Cl2 → CaCl2 + Ca(OCl)2 + 2H2O
Or simplified: Ca(OH)2 + Cl2 → CaCl(OCl) + H2O
Bleaching powder is a mixture of calcium hypochlorite and calcium chloride.
Frequently Asked Questions
What is the difference between strength and concentration of acids/bases?
Strength refers to the degree of ionization (strong acids/bases ionize completely, weak ones partially). Concentration refers to the amount of solute per unit volume of solution. A dilute strong acid can have lower concentration than a concentrated weak acid.
How does an indicator help in identifying acids and bases?
Indicators are substances that change color in acidic or basic solutions. For example, methyl orange turns red in acid and yellow in base; phenolphthalein is colorless in acid and pink in base. They help identify the pH of solutions.
More Class 10 Science PYQs
- Chemical Reactions and Equations
- Light (Reflection and Refraction)
- Electricity
- Metals and Non-metals
- Life Processes
- Heredity and Evolution
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