WILLER SELECT NEET 2027

Acids, Bases & Salts

Comprehensive Mastery Guide for NEET Aspirants

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This specially curated content is part of Willer Academy's NEET 2027 Strategic Preparation Program, designed by our expert faculty and AI-powered learning systems to give you a competitive edge.

Programmer Note: Willer Select students receive customized learning paths with this material optimized for NEET 2027 preparation, including spaced repetition scheduling and competency mapping.

I. Foundational Concepts

1. Acids

Definition: Substances that release hydrogen ions (H⁺) in aqueous solutions.

Key Properties:

• Sour taste (e.g., lemon, vinegar)
• Turn blue litmus → red
• Conduct electricity (due to mobile H⁺ ions)
• React with active metals to release H₂ gas

NEET Focus

Arrhenius Theory: Acids increase H⁺ concentration in water.

HCl → H⁺ + Cl⁻

Medical Connection: Stomach acid (HCl) helps digestion but excess causes acidity (treated with antacids).

2. Bases

Definition: Substances that release hydroxide ions (OH⁻) in water.

Key Properties:

• Bitter taste, soapy feel
• Turn red litmus → blue
• Conduct electricity (due to OH⁻ ions)

Teaching Demonstration

Test soap solution (pH ~10) with litmus paper to show base properties.

3. Salts

Definition: Ionic compounds formed by neutralization reactions (acid + base).

HCl + NaOH → NaCl + H₂O

NEET Relevance: Salt balance crucial in human physiology (electrolytes).

II. Core Theory & Mechanisms

1. pH Scale (0-14)

Measures H⁺ ion concentration:

• pH < 7: Acidic (higher H⁺ concentration)
• pH = 7: Neutral (pure water at 25°C)
• pH > 7: Basic (higher OH⁻ concentration)

Classroom Activity

Use pH strips to test various substances:

Substance	pH	Nature
Gastric juice	1.5-2.0	Strongly acidic
Blood	7.35-7.45	Slightly basic
Pancreatic fluid	8.1-8.3	Basic

2. Neutralization Reactions

H⁺(aq) + OH⁻(aq) → H₂O(l) ΔH = -57.3 kJ/mol (exothermic)

Medical Application

Antacids like Mg(OH)₂ neutralize excess stomach acid:

Mg(OH)₂ + 2HCl → MgCl₂ + 2H₂O

3. Metal-Acid Reactions

Zn + 2HCl → ZnCl₂ + H₂↑

Redox Mechanism

Oxidation: Zn → Zn²⁺ + 2e⁻

Reduction: 2H⁺ + 2e⁻ → H₂↑

III. Industrial Processes (NEET Weightage)

1. Chlor-Alkali Process (NaOH Production)

2NaCl(aq) + 2H₂O(l) → 2NaOH(aq) + Cl₂(g) + H₂(g)

Electrode	Reaction	Product
Anode (+ve)	2Cl⁻ → Cl₂ + 2e⁻	Chlorine gas
Cathode (-ve)	2H₂O + 2e⁻ → H₂ + 2OH⁻	Hydrogen gas + NaOH

NEET Trick

Remember: "A Cat Has No Clothes" for electrode products:

• Anode → Cl₂
• Cathode → H₂ + NaOH

2. Bleaching Powder (CaOCl₂)

Ca(OH)₂ + Cl₂ → CaOCl₂ + H₂O

Active Component: Hypochlorite ion (ClO⁻) acts as oxidizing agent.

IV. Willer Select NEET Optimization

For Willer Select Programmers

This content is tagged with:

• NEET 2027 competency codes: C3.1 (Acid-Base), C3.2 (Salts)
• Difficulty levels: Basic (70%), Moderate (25%), Advanced (5%)
• Recommended spaced repetition intervals: 1d, 7d, 30d

NEET Previous Year Questions Analysis

2022 Question: "Why doesn't dry HCl change litmus color?"

Key Concept: H⁺ ions are produced only in aqueous solution.

2021 Question: "Which salt is used in antacids?"

Answer: Sodium bicarbonate (NaHCO₃) or magnesium hydroxide [Mg(OH)₂].

Willer Memory Technique

"POP Goes the Bone":

• Plaster of Paris (CaSO₄·½H₂O) used for bone fractures

Willer Select NEET 2027 Roadmap

This content is part of our 3-Year NEET Preparation Program:

Year	Focus	Acids-Bases Milestone
2024-25	Concept Building	Mastery of basic reactions
2025-26	Application	Medical applications
2026-27	NEET Optimization	PYQ analysis & speed drills

Faculty Note

Willer Select students receive additional:

• Monthly competency assessments
• Personalized doubt-clearing sessions
• AI-generated practice tests

WILLER SELECT - NEET 2027

Acids, Bases & Salts - CBSE Class 10

Comprehensive Question Bank with Solutions

I. Indicators (5 Markers)

Indicator	Acid (pH < 7)	Base (pH > 7)	NEET Connection
Litmus	Red	Blue	Diagnostic tests
Phenolphthalein	Colorless	Pink	Titration experiments
Methyl Orange	Red	Yellow	Gastric pH analysis
Turmeric	Yellow	Reddish-brown	Natural pH detector

CBSE Practical Question:

Q: A student observes that onion smell vanishes when added to solution X but remains in solution Y. Identify X and Y.

A: X = Base (e.g., NaOH), Y = Acid (e.g., HCl). Onion is an olfactory indicator.

II. MCQs (20 Questions)

1. Which acid is present in ant sting?

(a) Citric acid

(b) Formic acid (Correct)

(c) Lactic acid

(d) Acetic acid

2. The pH of a solution decreases from 7 to 2. This means:

(a) Solution becomes more basic

(b) Solution becomes more acidic (Correct)

(c) No change in acidity

(d) Solution becomes neutral

20. Plaster of Paris hardens by:

(a) Combining with water (Correct)

(b) Losing water

(c) Oxidation

(d) Reduction

III. Assertion-Reasoning (5 Questions)

1. Assertion (A): Dry HCl gas doesn't change the color of litmus paper.

Reason (R): H⁺ ions are produced only in aqueous solution.

Answer: Both A and R are true, and R explains A.

2. Assertion (A): Sodium carbonate is called washing soda.

Reason (R): It is used for water softening.

Answer: Both A and R are true, but R doesn't explain A.

5. Assertion (A): Antacids contain bases like Mg(OH)₂.

Reason (R): They neutralize excess stomach acid.

Answer: Both A and R are true, and R explains A.

IV. Practical-Based Questions (10 Marks)

Experiment 1: Neutralization Reaction

Procedure:

1. Take 10ml dilute NaOH in a conical flask
2. Add 2 drops phenolphthalein (turns pink)
3. Add dilute HCl dropwise until color disappears

Observation: Pink → colorless (endpoint reached)

Precaution: Swirl the flask continuously

Experiment 2: Metal-Acid Reaction

Question: Why does copper not react with dilute HCl?

Answer: Copper is below hydrogen in reactivity series.

V. Previous Year CBSE Questions (2020-2024)

2024 Q: Which salt is used in fire extinguishers?

Answer: Sodium bicarbonate (NaHCO₃)

2023 Q: Name the acid present in tamarind.

Answer: Tartaric acid

2022 Q: What happens when Plaster of Paris mixes with water?

Answer: Hardens to form gypsum (CaSO₄·2H₂O)

Willer Select NEET 2027 Special

Competency Mapping

Topic	CBSE Marks	NEET Relevance
pH Concept	3	Blood pH regulation
Salt Preparation	4	Medicinal salts

AI-Powered Analysis

Willer Select students receive:

• Personalized question recommendations
• Difficulty-adjusted practice sets
• Performance analytics dashboard

Class 10 Chemistry: Acids, Bases and Salts

Complete Question Bank with Answers

Short Answer Questions (2 Marks Each)

1. Why does dry HCl gas not change the color of dry litmus paper?

Dry HCl gas doesn't contain free H⁺ ions. Litmus changes color only in the presence of H⁺ ions which are formed when HCl dissolves in water (HCl + H₂O → H₃O⁺ + Cl⁻).

2. What happens when Plaster of Paris is mixed with water?

Plaster of Paris (CaSO₄·½H₂O) reacts with water to form gypsum (CaSO₄·2H₂O) and hardens:

CaSO₄·½H₂O + 1½H₂O → CaSO₄·2H₂O

This hardening property makes it useful for making casts, sculptures, and wall plasters.

3. Name the acid present in ant sting and give its chemical formula.

Formic acid (Methanoic acid), Chemical formula: HCOOH

It causes irritation and burning sensation when ants bite. Rubbing baking soda (a base) neutralizes the effect.

4. Why is sodium hydrogen carbonate used as an antacid?

Sodium hydrogen carbonate (NaHCO₃) is a mild base that neutralizes excess stomach acid (HCl):

NaHCO₃ + HCl → NaCl + H₂O + CO₂

It provides quick relief from acidity and heartburn.

5. What is the chemical name and formula of bleaching powder?

Chemical name: Calcium oxychloride

Formula: CaOCl₂

It is produced by the reaction: Ca(OH)₂ + Cl₂ → CaOCl₂ + H₂O

6. Why does distilled water not conduct electricity?

Distilled water lacks ions (H⁺ and OH⁻) in sufficient concentration to conduct electricity. Pure water has very low dissociation (H₂O ⇌ H⁺ + OH⁻) with only 1×10⁻⁷ M of each ion at 25°C.

7. What is the pH range of acidic, basic and neutral solutions?

• Acidic solutions: pH < 7
• Neutral solutions: pH = 7
• Basic solutions: pH > 7

The pH scale ranges from 0 (most acidic) to 14 (most basic).

8. Give two examples of olfactory indicators.

1. Onion: Smell disappears in basic solution but remains in acidic solution
2. Vanilla: Smell disappears in basic solution but remains in acidic solution

These indicators change their smell in acidic or basic media.

9. What happens when carbon dioxide is passed through lime water?

When CO₂ is passed through lime water [Ca(OH)₂], it turns milky due to formation of insoluble calcium carbonate:

Ca(OH)₂ + CO₂ → CaCO₃↓ + H₂O

With excess CO₂, the milkiness disappears as soluble calcium bicarbonate forms:

CaCO₃ + H₂O + CO₂ → Ca(HCO₃)₂

10. Why do acids not show acidic behavior in absence of water?

Acids show acidic behavior only when H⁺ ions are released, which requires water. In absence of water:

• Acids remain in molecular form (e.g., HCl as molecules)
• No free H⁺ ions are available to show acidic properties
• Water helps in ionization: HCl + H₂O → H₃O⁺ + Cl⁻

Assertion-Reasoning Questions (3 Marks Each)

1. Assertion (A): Sodium hydroxide is called caustic soda.
Reason (R): It is highly corrosive and can cause severe burns.

Answer: Both A and R are true and R is the correct explanation of A.

Explanation: NaOH is called caustic soda because of its highly corrosive nature that can burn skin and other tissues. The term "caustic" refers to its ability to corrode or burn organic matter.

2. Assertion (A): Baking soda is used in fire extinguishers.
Reason (R): It decomposes to produce carbon dioxide gas when heated.

Answer: Both A and R are true and R is the correct explanation of A.

Explanation: Baking soda (NaHCO₃) decomposes when heated to produce CO₂ gas which helps in extinguishing fires by cutting off oxygen supply:

2NaHCO₃ → Na₂CO₃ + H₂O + CO₂

3. Assertion (A): Tooth decay starts when pH of mouth falls below 5.5.
Reason (R): Acid produced by bacteria dissolves calcium phosphate of tooth enamel.

Answer: Both A and R are true and R is the correct explanation of A.

Explanation: Bacteria in mouth produce acids (pH < 5.5) by fermentation of food particles. These acids react with calcium phosphate [Ca₃(PO₄)₂] of enamel causing tooth decay.

4. Assertion (A): Copper does not react with dilute hydrochloric acid.
Reason (R): Copper is below hydrogen in the reactivity series.

Answer: Both A and R are true and R is the correct explanation of A.

Explanation: Metals below hydrogen in reactivity series cannot displace hydrogen from acids. Copper (Cu) being less reactive than hydrogen doesn't react with dilute HCl.

5. Assertion (A): Farmers add slaked lime to acidic soils.
Reason (R): Slaked lime is a base that neutralizes soil acidity.

Answer: Both A and R are true and R is the correct explanation of A.

Explanation: Slaked lime [Ca(OH)₂] is added to acidic soils to neutralize excess acids and bring pH to optimal level (6-7) for plant growth:

Ca(OH)₂ + 2H⁺ → Ca²⁺ + 2H₂O

Long Answer Questions (5 Marks Each)

1. Explain the chlor-alkali process with labeled diagram. Write chemical equations involved and mention two uses of each product.

Chlor-alkali Process: Electrolysis of concentrated NaCl solution (brine)

Process Description:

1. Concentrated NaCl solution is electrolyzed using inert electrodes
2. Chlorine gas is produced at anode
3. Hydrogen gas at cathode
4. Sodium hydroxide solution forms near cathode

Chemical Equations:

At anode (Oxidation): 2Cl⁻ → Cl₂ + 2e⁻

At cathode (Reduction): 2H₂O + 2e⁻ → H₂ + 2OH⁻

Overall reaction: 2NaCl + 2H₂O → 2NaOH + Cl₂ + H₂

Uses of Products:

Product	Uses
Chlorine (Cl₂)	Water treatment/disinfection PVC plastic production
Hydrogen (H₂)	Fuel for rockets Ammonia production (Haber process)
Sodium hydroxide (NaOH)	Soap and detergent manufacturing Paper production

2. What is pH scale? How is it significant in everyday life? Give three examples.

pH Scale: A logarithmic scale (0-14) that measures hydrogen ion concentration in a solution:

pH = -log[H⁺]

Where [H⁺] is hydrogen ion concentration in moles per liter

Significance in Daily Life:

1. Digestive System:
   • Stomach pH ~1.5 (HCl) helps activate pepsin enzyme for protein digestion
   • Heartburn occurs when stomach acid refluxes into esophagus (pH ~6-7)
2. Tooth Care:
   • Tooth enamel (calcium phosphate) dissolves at pH < 5.5
   • Bacteria produce acids from food debris, lowering mouth pH
   • Toothpaste is basic (pH ~8) to neutralize acids
3. Agriculture:
   • Most crops grow best in soil pH 6-7
   • Acidic soils (pH < 5) are treated with lime [Ca(OH)₂]
   • Basic soils (pH > 8) are treated with organic matter
4. Blood pH:
   • Maintained at 7.35-7.45 for proper enzyme function
   • pH < 7.35 (acidosis) or > 7.45 (alkalosis) can be life-threatening

3. Describe the preparation, properties and uses of baking soda. Write chemical equations involved.

Preparation of Baking Soda (NaHCO₃):

Produced by Solvay process:

NaCl + NH₃ + CO₂ + H₂O → NaHCO₃ + NH₄Cl

Properties:

• White crystalline solid
• Mildly alkaline (pH ~8.4)
• Decomposes on heating: 2NaHCO₃ → Na₂CO₃ + H₂O + CO₂
• Reacts with acids: NaHCO₃ + HCl → NaCl + H₂O + CO₂

Uses:

1. Antacid: Neutralizes excess stomach acid
2. Baking: Produces CO₂ making cakes fluffy
3. Fire Extinguisher: Releases CO₂ which smothers fires
4. Cleaning Agent: Mild abrasive and deodorizer
5. Preparation of baking powder: Mixed with tartaric acid

4. Explain how acids and bases are identified using (a) litmus paper (b) phenolphthalein (c) methyl orange. Give color changes observed.

Indicator Tests:

Indicator	Acid	Base	Neutral
Litmus paper	Blue → Red	Red → Blue	No change (purple)
Phenolphthalein	Colorless	Colorless → Pink	Colorless
Methyl orange	Red	Yellow	Orange

Mechanism:

• Litmus: Weak acid that changes structure at different pH
• Phenolphthalein: Colorless in acid (pH < 8.3), pink in base (pH > 10)
• Methyl orange: Red at pH < 3.1, yellow at pH > 4.4

Practical Applications:

1. Litmus: Quick acid/base test
2. Phenolphthalein: Used in strong acid-strong base titrations
3. Methyl orange: Used in weak base-strong acid titrations

5. Differentiate between acids and bases with three properties each. Give two examples of each that you use in daily life.

Differences:

Property	Acids	Bases
Taste	Sour (e.g., lemon)	Bitter (e.g., baking soda)
Touch	No characteristic feel	Soapy/slippery
Litmus Test	Blue → Red	Red → Blue
pH	< 7	> 7
Reaction with metals	Produce H₂ gas	No reaction (except Al, Zn)

Daily Life Examples:

Acids	Bases
Citric acid (lemons, oranges) Acetic acid (vinegar)	Sodium hydroxide (soap, drain cleaner) Magnesium hydroxide (antacid tablets)

Neutralization Reaction Example:

HCl + NaOH → NaCl + H₂O

(Stomach acid) + (Antacid) → (Salt) + (Water)