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Chemical Properties of Acids and Bases

🎓 Class 10 Science CBSE Theory Ch 2 — Acids, Bases and Salts ⏱ ~23 min
🌐 Language: [gtranslate]

This MCQ module is based on: Chemical Properties of Acids and Bases

[myaischool_lt_science_assessment grade_level="class_10" science_domain="chemistry" difficulty="intermediate"]

Introduction: Acids, Bases and Their Indicators

You already know from everyday life that a lemon tastes sour and soap feels slippery. The sour taste is due to the presence of an acid, while the slippery nature of soap is because it contains a base. But tasting substances in a laboratory is extremely dangerous! So scientists use special substances called indicators to test whether a substance is acidic or basic.

IndicatorColour in AcidColour in Base
Litmus (blue)Turns redRemains blue
Litmus (red)Remains redTurns blue
TurmericRemains yellowTurns red/brown
Methyl orangeRed/pinkYellow
PhenolphthaleinColourlessPink/magenta
Key Idea: Indicators help us classify substances as acidic, basic or neutral without tasting them. Litmus paper is the most commonly used indicator in school laboratories.

2.1 Understanding the Chemical Properties of Acids and Bases

In this section, we will systematically explore how acids and bases behave when they react with metals, with each other, and with metal carbonates and bicarbonates. Each reaction reveals important chemical behaviour.

2.1.1 How Do Acids and Bases React with Metals?

Activity 2.1 — Metals Reacting with Dilute Acids L3 Apply
Predict first: When you place a piece of zinc or magnesium into dilute hydrochloric acid, what do you expect to see? What gas might form?
  1. Set up the apparatus as shown in Fig 2.1. Take a few pieces of zinc granules in a test tube.
  2. Add about 5 mL of dilute hydrochloric acid (HCl) to the test tube.
  3. Observe the surface of the metal carefully for bubbles.
  4. Bring a burning matchstick (or candle) near the mouth of the test tube. Listen for a sound.
  5. Repeat the experiment using dilute sulphuric acid (H2SO4) and metals like magnesium (Mg) and iron (Fe).
Observations:
Bubbles of gas are produced at the surface of the metal. When a burning matchstick is brought to the mouth of the test tube, a pop sound is heard. This confirms the gas is hydrogen (H2).

Chemical equations:
\(\text{Zn}(s) + 2\text{HCl}(aq) \rightarrow \text{ZnCl}_2(aq) + \text{H}_2(g)\uparrow\)
\(\text{Mg}(s) + 2\text{HCl}(aq) \rightarrow \text{MgCl}_2(aq) + \text{H}_2(g)\uparrow\)
\(\text{Fe}(s) + \text{H}_2\text{SO}_4(aq) \rightarrow \text{FeSO}_4(aq) + \text{H}_2(g)\uparrow\)
General pattern: Metal + Dilute Acid → Salt + Hydrogen gas
H₂ gas ↑ Pop sound! Dilute HCl Zn granules Test tube with delivery tube Water trough Gas jar
Fig 2.1: Zinc granules reacting with dilute HCl. Hydrogen gas is collected over water and tested with a burning splint (pop sound).
Activity 2.2 — Metals Reacting with Bases L3 Apply
Predict first: Acids react with metals to produce hydrogen. Do you think bases can also produce hydrogen when reacted with metals?
  1. Take a few pieces of zinc granules in a test tube and add sodium hydroxide (NaOH) solution.
  2. Observe for any gas evolution. Test the gas with a burning splint.
  3. Repeat with aluminium foil/granules instead of zinc.
Observations:
Bubbles appear and the gas again burns with a pop sound, confirming it is hydrogen.

Chemical equations:
\(2\text{NaOH}(aq) + \text{Zn}(s) \rightarrow \text{Na}_2\text{ZnO}_2(aq) + \text{H}_2(g)\uparrow\)

Sodium zincate

\(2\text{NaOH}(aq) + 2\text{Al}(s) + 2\text{H}_2\text{O}(l) \rightarrow 2\text{NaAlO}_2(aq) + 3\text{H}_2(g)\uparrow\)

Sodium aluminate

Conclusion: Both acids and certain bases react with metals to produce hydrogen gas. However, not all metals react with bases — only amphoteric metals like zinc and aluminium do.
Important: The reaction of bases with metals is not as common as acids with metals. Only certain metals such as zinc (Zn) and aluminium (Al) react with strong bases like NaOH to liberate hydrogen gas.

2.1.2 How Do Acids and Bases React with Each Other?

Activity 2.3 — Neutralisation Reaction L3 Apply
Predict first: What happens when an acid and a base are mixed together? Will the resulting solution be acidic, basic, or something else?
  1. Take about 2 mL of NaOH solution in a test tube and add a few drops of phenolphthalein indicator. The solution turns pink.
  2. Now add dilute HCl drop by drop while swirling the tube.
  3. Continue until the pink colour just disappears. The solution is now neutral.
  4. Touch the bottom of the test tube — you will feel warmth.
Observations:
The pink colour disappears when enough HCl is added, indicating the base has been fully neutralised. The test tube feels warm because the reaction is exothermic (releases heat).

Chemical equation:
\(\text{NaOH}(aq) + \text{HCl}(aq) \rightarrow \text{NaCl}(aq) + \text{H}_2\text{O}(l)\)
General pattern:
Acid + Base → Salt + Water

This reaction is called a neutralisation reaction. The salt produced (NaCl) and water are the products. Energy is released in the form of heat.

Neutralisation: When an acid reacts with a base, they neutralise each other forming a salt and water. This is accompanied by the release of heat energy (exothermic process).
Activity 2.4 — Reaction of Metallic Oxides with Acids L3 Apply
Predict first: Metallic oxides are basic in nature. If we mix a metallic oxide with an acid, will a neutralisation-like reaction occur?
  1. Take a small quantity of copper oxide (CuO) — a black powder — in a beaker.
  2. Add dilute hydrochloric acid slowly while stirring.
  3. Observe the colour change of the solution.
Observations:
The black copper oxide dissolves and the solution turns blue-green, which is the colour of copper chloride (CuCl2) solution.

\(\text{CuO}(s) + 2\text{HCl}(aq) \rightarrow \text{CuCl}_2(aq) + \text{H}_2\text{O}(l)\)

This confirms that metallic oxides are basic in nature — they react with acids just like bases do, producing a salt and water.

2.1.3 How Do Metal Carbonates and Bicarbonates React with Acids?

Activity 2.5 — Carbonates/Bicarbonates Reacting with Acids L3 Apply
Predict first: When you add vinegar (acid) to baking soda (NaHCO₃), you see fizzing. What gas do you think is produced?
  1. Set up the apparatus as shown in Fig 2.3. Take a test tube with sodium carbonate (Na2CO3) or sodium bicarbonate (NaHCO3).
  2. Add dilute hydrochloric acid to it.
  3. Pass the gas produced through freshly prepared lime water — Ca(OH)2 solution.
  4. Observe what happens to the lime water.
Observations:
Brisk effervescence occurs. The gas turns the lime water milky, confirming it is carbon dioxide (CO2).

Chemical equations:
\(\text{Na}_2\text{CO}_3(s) + 2\text{HCl}(aq) \rightarrow 2\text{NaCl}(aq) + \text{H}_2\text{O}(l) + \text{CO}_2(g)\uparrow\)
\(\text{NaHCO}_3(s) + \text{HCl}(aq) \rightarrow \text{NaCl}(aq) + \text{H}_2\text{O}(l) + \text{CO}_2(g)\uparrow\)
General pattern:
Metal carbonate/bicarbonate + Acid → Salt + Water + CO₂
Lime water test:
\(\text{Ca(OH)}_2(aq) + \text{CO}_2(g) \rightarrow \text{CaCO}_3(s)\downarrow + \text{H}_2\text{O}(l)\)

The white precipitate of calcium carbonate (CaCO3) makes the lime water appear milky. This is the standard test for carbon dioxide gas.

Test tube A Na₂CO₃ + dil. HCl CO₂ gas Test tube B Lime water Ca(OH)₂ Turns milky! Why does lime water turn milky? Ca(OH)₂ + CO₂ → CaCO₃↓ + H₂O The white precipitate of calcium carbonate (CaCO₃) makes the solution appear milky.
Fig 2.3: CO2 gas produced from the reaction of sodium carbonate with dilute HCl is passed through lime water, which turns milky due to the formation of insoluble CaCO3.

Similarly, when limestone (calcium carbonate, CaCO3) reacts with dilute hydrochloric acid:

\(\text{CaCO}_3(s) + 2\text{HCl}(aq) \rightarrow \text{CaCl}_2(aq) + \text{H}_2\text{O}(l) + \text{CO}_2(g)\uparrow\)
Summary of Reactions:
  • Metal + Acid → Salt + Hydrogen gas (H2)
  • Base + Metal → Salt + Hydrogen gas (for Zn, Al)
  • Acid + Base → Salt + Water (neutralisation)
  • Acid + Metal carbonate/bicarbonate → Salt + Water + CO2
  • Acid + Metal oxide → Salt + Water

Competency-Based Questions

In a chemistry practical, Ananya took three test tubes: Tube A contained zinc granules with dilute HCl, Tube B had NaOH solution with zinc, and Tube C contained Na2CO3 with dilute H2SO4. She tested each gas produced with a burning splint or lime water.

Q1. L1 Remember What is the general reaction when an acid reacts with a metal?

  • A. Metal + Acid → Salt + Oxygen
  • B. Metal + Acid → Salt + Hydrogen
  • C. Metal + Acid → Salt + Water
  • D. Metal + Acid → Metal oxide + Hydrogen
Answer: B. When a metal reacts with a dilute acid, a salt and hydrogen gas are produced. The hydrogen gas can be confirmed by the pop-sound test with a burning splint.

Q2. L2 Understand In Tube C, the gas turned lime water milky. Write the balanced equation for the reaction of Na2CO3 with dilute H2SO4. Identify the gas. (2 marks)

Answer:
\(\text{Na}_2\text{CO}_3(s) + \text{H}_2\text{SO}_4(aq) \rightarrow \text{Na}_2\text{SO}_4(aq) + \text{H}_2\text{O}(l) + \text{CO}_2(g)\uparrow\)
The gas produced is carbon dioxide (CO2), which turns lime water milky by forming insoluble calcium carbonate: Ca(OH)2 + CO2 → CaCO3↓ + H2O.

Q3. L4 Analyse Both Tube A and Tube B produce the same gas when tested with a burning splint. What does this tell us about the reaction of bases with metals? (3 marks)

Answer: Both tubes produce hydrogen gas (confirmed by the pop sound). This demonstrates that bases, like acids, can also react with certain metals (such as zinc and aluminium) to produce hydrogen gas. However, unlike acids which react with most metals, only specific metals that are amphoteric (react with both acids and bases) show this behaviour with bases. For zinc: 2NaOH(aq) + Zn(s) → Na2ZnO2(aq) + H2(g).

Q4. L3 Apply A student added dilute HCl to baking soda (NaHCO3) and passed the resulting gas into lime water. Write two balanced equations for: (i) the reaction of NaHCO3 with HCl, and (ii) the reaction of CO2 with lime water. (3 marks)

Answer:
(i) \(\text{NaHCO}_3(s) + \text{HCl}(aq) \rightarrow \text{NaCl}(aq) + \text{H}_2\text{O}(l) + \text{CO}_2(g)\uparrow\)
(ii) \(\text{Ca(OH)}_2(aq) + \text{CO}_2(g) \rightarrow \text{CaCO}_3(s)\downarrow + \text{H}_2\text{O}(l)\)
The white precipitate of CaCO3 causes the lime water to appear milky.

Q5. L5 Evaluate Rahul claims: "All metals react with NaOH to produce hydrogen gas." Is this statement correct? Justify your answer with examples. (3 marks)

Answer: Rahul's statement is incorrect. Not all metals react with NaOH. Only certain metals like zinc and aluminium, which are amphoteric in nature, react with NaOH to produce hydrogen gas. Metals such as iron (Fe), copper (Cu), and gold (Au) do not react with NaOH. For example, Zn reacts: 2NaOH + Zn → Na2ZnO2 + H2↑, but iron does not react with NaOH solution under normal conditions.

Assertion-Reason Questions

Assertion (A): When zinc reacts with dilute hydrochloric acid, zinc chloride and hydrogen gas are formed.

Reason (R): Hydrogen gas burns with a pop sound when a burning splint is brought near it.

  • A. Both A and R are true, and R is the correct explanation of A.
  • B. Both A and R are true, but R is NOT the correct explanation of A.
  • C. A is true, but R is false.
  • D. A is false, but R is true.
Answer: B. Both statements are true. Zinc does react with dilute HCl to form ZnCl2 and H2. Hydrogen gas does burn with a pop sound. However, the pop sound test (R) is a method to identify hydrogen gas, not the reason for its formation. The reason hydrogen forms is because the acid donates H+ ions which get reduced to H2.

Assertion (A): When CO2 gas is passed through lime water, it turns milky.

Reason (R): CO2 reacts with calcium hydroxide to form insoluble calcium carbonate.

  • A. Both A and R are true, and R is the correct explanation of A.
  • B. Both A and R are true, but R is NOT the correct explanation of A.
  • C. A is true, but R is false.
  • D. A is false, but R is true.
Answer: A. Both are true and R correctly explains A. CO2 reacts with Ca(OH)2 to form CaCO3 (insoluble white precipitate) + H2O. This white precipitate of CaCO3 suspended in the solution makes the lime water look milky.

Assertion (A): Neutralisation is an exothermic reaction.

Reason (R): In a neutralisation reaction, an acid and a base react to form salt and water with the release of heat.

  • A. Both A and R are true, and R is the correct explanation of A.
  • B. Both A and R are true, but R is NOT the correct explanation of A.
  • C. A is true, but R is false.
  • D. A is false, but R is true.
Answer: A. Both are true and R correctly explains A. Neutralisation always releases heat energy, making the test tube feel warm. NaOH + HCl → NaCl + H2O + Heat. The reason accurately describes what happens and explains why the reaction is exothermic.

Did You Know?

Frequently Asked Questions — Chemical Properties of Acids and Bases

What is chemical properties of acids and bases in Class 10 Science (CBSE board)?

Chemical Properties of Acids and Bases is a key topic in NCERT Class 10 Science Chapter 2 — Acids, Bases and Salts. It explains chemical properties of acids and bases — reactions with metals, carbonates, oxides and neutralisation. Core ideas covered include acid, base, indicator, litmus. Mastering this subtopic is essential for scoring well in the CBSE Class 10 Science board exam because board papers repeatedly test these concepts through MCQs, short answers and long-answer questions. This part gives a complete, exam-ready explanation with activities, diagrams and competency-based practice aligned to NCERT.

Why is acid important in NCERT Class 10 Science?

Acid is important in NCERT Class 10 Science because it forms the foundation for understanding chemical properties of acids and bases in Chapter 2 — Acids, Bases and Salts. Without a clear idea of acid, students cannot answer higher-order CBSE board questions involving base, indicator, litmus. Board papers regularly include 2-mark and 3-mark questions on this concept, and competency-based questions often link acid to real-life situations. Building clarity here pays off directly in board marks.

How is chemical properties of acids and bases tested in the Class 10 Science CBSE board exam?

The CBSE Class 10 Science board exam tests chemical properties of acids and bases through a mix of 1-mark MCQs, 2-mark short answers, 3-mark explanations with examples, 5-mark descriptive questions (often with diagrams or balanced equations) and 4-mark competency-based questions. Expect direct questions on acid, base, indicator and application-based questions drawn from NCERT activities. Students who follow NCERT thoroughly and practice this chapter's questions consistently score in the 90%+ range.

What are the key terms to remember for chemical properties of acids and bases in Class 10 Science?

The key terms to remember for chemical properties of acids and bases in NCERT Class 10 Science Chapter 2 are: acid, base, indicator, litmus, neutralisation reaction, metal carbonate reaction. Each of these concepts carries exam weightage and regularly appears in the CBSE board paper. Write clear one-line definitions of every term in your revision notes and revisit them before the exam. Linking these terms visually through a flowchart or concept map makes recall easier during the Class 10 Science board exam.

Is Chemical Properties of Acids and Bases included in the Class 10 Science syllabus for 2025–26 CBSE board exam?

Yes, Chemical Properties of Acids and Bases is a part of the NCERT Class 10 Science syllabus (2025–26) prescribed by CBSE. It falls under Chapter 2 — Acids, Bases and Salts — and is examined in the annual board paper. The current syllabus retains the full treatment of acid, base, indicator as per the NCERT textbook. Because CBSE bases every board question on NCERT, studying this part thoroughly ensures complete syllabus coverage and guarantees marks from this chapter.

How should I prepare chemical properties of acids and bases for the CBSE Class 10 Science board exam?

Prepare chemical properties of acids and bases for the CBSE Class 10 Science board exam in three steps. First, read this NCERT part carefully, highlighting definitions and diagrams of acid, base, indicator. Second, solve every in-text question and end-of-chapter exercise — CBSE questions often come directly from NCERT. Third, practice competency-based and assertion-reason questions to sharpen reasoning. Write answers in the exam-style format (point-wise with diagrams) and time yourself. This method delivers confidence and full marks in the board exam.

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