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Practice Class 10 Science Chapter 2 – Acids, Bases and Salts with 5 NCERT-based MCQs on acid-base indicators, pH, hydronium ions, strength of acids and bases, and chemical properties of acidic and basic solutions.
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Chapter Information
Subject: Science
Class: 10
Chapter: Acids, Bases and Salts
Question Type: Multiple Choice Questions (MCQs)
Practice Set: 2
Difficulty Level: Moderate
Based On: NCERT Syllabus
Introduction
The acidic and basic nature of a solution depends on the ions present in it. When acids dissolve in water, they produce hydronium ions (H₃O⁺), while bases produce hydroxide ions.
The pH scale is used to measure how acidic or basic a solution is. Understanding pH and the role of water in producing ions is important for solving conceptual questions from this chapter.
This Practice Set 2 focuses on hydronium ions, pH, strength of acids and bases, and indicators.
What You Will Learn
✔ Hydronium ions
✔ Formation of H₃O⁺ ions
✔ pH scale
✔ Acidic and basic solutions
✔ Strength of acids and bases
✔ Universal indicator
✔ Relationship between pH and hydrogen ion concentration
Why This Topic Is Important
The pH scale is one of the most important concepts in the chapter. Questions may ask students to compare solutions according to their pH values or identify whether a solution is acidic, neutral or basic.
Understanding hydronium ions also helps explain why acids show their acidic properties in aqueous solutions.
5 MCQs with Answers and Detailed Solutions
Q1. What happens when hydrogen chloride gas is dissolved in water?
A) It produces sodium ions
B) It produces hydronium ions
C) It produces hydroxide ions only
D) It produces calcium ions
Answer: B) It produces hydronium ions
Detailed Solution
Hydrogen chloride (HCl) dissolves in water and forms hydronium ions.
The reaction can be represented as:
HCl + H₂O → H₃O⁺ + Cl⁻
The formation of H₃O⁺ ions is responsible for the acidic nature of the solution.
Therefore, the correct answer is B) It produces hydronium ions.
Exam Tip
Remember:
H⁺ + H₂O → H₃O⁺
In aqueous solution, hydrogen ions are associated with water molecules as hydronium ions.
Q2. Which solution has the highest concentration of hydrogen ions?
A) pH 2
B) pH 5
C) pH 7
D) pH 10
Answer: A) pH 2
Detailed Solution
The pH scale is related to the concentration of hydrogen ions.
A lower pH value means a higher concentration of hydrogen ions and therefore a more acidic solution.
Among the given values:
- pH 2 → strongly acidic
- pH 5 → acidic
- pH 7 → neutral
- pH 10 → basic
Therefore, the solution with pH 2 has the highest hydrogen ion concentration.
Hence, the correct answer is A.
Exam Tip
Remember:
Lower pH → More acidic → Higher H⁺ concentration
Higher pH → More basic → Lower H⁺ concentration
Q3. Which of the following represents a neutral solution at approximately room temperature?
A) pH 2
B) pH 5
C) pH 7
D) pH 12
Answer: C) pH 7
Detailed Solution
A neutral solution has approximately equal concentrations of hydrogen ions and hydroxide ions.
At around room temperature, a neutral aqueous solution has a pH of about 7.
For comparison:
- pH less than 7 → Acidic
- pH 7 → Neutral
- pH greater than 7 → Basic
Therefore, the correct answer is C) pH 7.
Exam Tip
The basic pH classification is:
pH < 7 → Acidic
pH = 7 → Neutral
pH > 7 → Basic
Q4. Which of the following solutions is the most basic?
A) pH 3
B) pH 6
C) pH 8
D) pH 12
Answer: D) pH 12
Detailed Solution
A solution becomes increasingly basic as its pH increases.
Among the given options, pH 12 is the highest value.
Therefore, it represents the most basic solution.
The order from more acidic to more basic is:
pH 3 → pH 6 → pH 8 → pH 12
Hence, the correct answer is D) pH 12.
Exam Tip
For pH comparison:
Lower pH = More acidic
Higher pH = More basic
Q5. Which indicator gives different colours over a range of pH values and is commonly used to estimate the pH of a solution?
A) Universal indicator
B) Sodium chloride
C) Copper sulphate
D) Distilled water
Answer: A) Universal indicator
Detailed Solution
A universal indicator is a mixture of several indicators that shows different colours at different pH values.
It can therefore be used to estimate the approximate pH of a solution.
The colour obtained is compared with a standard pH colour chart.
Thus, universal indicator is more useful for estimating pH than a single indicator that generally gives a limited colour change.
Therefore, the correct answer is A) Universal indicator.
Exam Tip
Remember:
Universal indicator → Different colours at different pH values → Approximate pH
Important Concepts
1. Hydronium Ion
When an acid dissolves in water, it produces hydrogen ions. These hydrogen ions combine with water molecules to form hydronium ions (H₃O⁺).
H⁺ + H₂O → H₃O⁺
The presence of hydronium ions gives an aqueous solution its acidic character.
2. pH Scale
The pH scale is used to express the acidic or basic nature of a solution.
Generally:
pH < 7 → Acidic
pH = 7 → Neutral
pH > 7 → Basic
3. Hydrogen Ion Concentration
The acidic strength of an aqueous solution is related to its hydrogen ion concentration.
A higher concentration of hydrogen ions corresponds to a lower pH.
Therefore:
Higher H⁺ concentration → Lower pH
4. Universal Indicator
A universal indicator gives different colours over a range of pH values.
It is useful for estimating the approximate pH of a solution.
5. Strength of Acids and Bases
The strength of an acid or base is related to the extent to which it ionises in aqueous solution.
A strong acid produces a relatively high concentration of hydrogen ions in solution, while a weak acid produces a lower concentration.
Similarly, strong and weak bases differ in their extent of ionisation.
Related Practice Questions
Q1. What is a hydronium ion?
Q2. What does a low pH value indicate?
Q3. What is the pH of a neutral solution at approximately room temperature?
Q4. Which solution is more acidic: pH 3 or pH 5?
Q5. Why is a universal indicator useful?
Mini Quiz Challenge
Try answering these questions within 60 seconds.
Q1. Which ion is responsible for the acidic nature of an aqueous solution?
A) H₃O⁺
B) Na⁺
C) Cl⁻
D) Ca²⁺
Q2. Which pH value represents the most acidic solution?
A) 2
B) 6
C) 8
D) 11
Q3. A solution with pH 9 is:
A) Strongly acidic
B) Weakly acidic
C) Neutral
D) Basic
Q4. What happens to acidity when hydrogen ion concentration increases?
A) Acidity increases
B) Acidity decreases
C) It becomes neutral
D) No change occurs
Q5. Which indicator can be used to estimate the approximate pH of a solution?
A) Universal indicator
B) Sodium chloride
C) Copper sulphate
D) Water
Exam Tips
✔ Remember the formation of H₃O⁺ ions.
✔ Learn the basic classification of the pH scale.
✔ Remember that lower pH means greater acidity.
✔ Remember that higher pH means greater basicity.
✔ Practise comparing solutions based on their pH values.
✔ Understand the difference between indicators and the pH scale.
✔ Learn the role of universal indicator in estimating pH.
Quick Revision Notes
✔ Hydronium ion: H₃O⁺
✔ Hydronium formation: H⁺ + H₂O → H₃O⁺
✔ pH < 7: Acidic
✔ pH = 7: Neutral at approximately room temperature
✔ pH > 7: Basic
✔ Lower pH: Higher hydrogen ion concentration
✔ Higher pH: Lower hydrogen ion concentration
✔ Universal indicator: Used to estimate approximate pH through colour changes
Common Mistakes Students Make
❌ Thinking that a higher pH value means greater acidity.
❌ Confusing hydrogen ions with hydroxide ions.
❌ Forgetting the formation of hydronium ions in water.
❌ Treating every indicator as a universal indicator.
❌ Assuming that pH 7 is acidic.
❌ Confusing the strength of an acid with the amount of acid present in a solution.
Key Takeaways
✔ Acids produce hydronium ions in aqueous solution.
✔ Hydrogen ions associate with water molecules to form H₃O⁺.
✔ The pH scale indicates the acidic or basic nature of a solution.
✔ Lower pH values indicate greater acidity.
✔ Higher pH values indicate greater basicity.
✔ A pH of about 7 represents a neutral aqueous solution at approximately room temperature.
✔ Universal indicator helps estimate the approximate pH of a solution.
FAQs
Q. What is a hydronium ion?
Answer:
A hydronium ion is H₃O⁺, formed when a hydrogen ion combines with a water molecule.
Q. What does a low pH value indicate?
Answer:
A low pH value indicates a higher hydrogen ion concentration and therefore greater acidity.
Q. What is the pH of a neutral solution?
Answer:
At approximately room temperature, a neutral aqueous solution has a pH of about 7.
Q. Which is more basic, pH 8 or pH 12?
Answer:
pH 12 is more basic because a higher pH indicates greater basicity.
Q. What is the use of a universal indicator?
Answer:
A universal indicator gives different colours at different pH values and can be used to estimate the approximate pH of a solution.
Conclusion
Class 10 Science Chapter 2 – Acids, Bases and Salts focuses on hydronium ions, hydrogen ion concentration, the pH scale, universal indicators and the acidic or basic nature of solutions.
Understanding these concepts is important for solving numerical, conceptual and application-based questions related to pH and the strength of acids and bases.
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