Acids, Bases and Salts: Chemical Properties and Applications
Learning Outcomes
- Identify acids and bases using natural and synthetic indicators
- Explain the chemical properties of acids and bases with metals, metal carbonates and each other
- Understand the pH scale and its importance in everyday life
- Describe the process of neutralization and its applications
- Prepare common salts and understand their properties and uses
- Explain the importance of acids, bases and salts in daily life
Starter Questions
- Why do acids taste sour while bases taste bitter?
- How does litmus paper help identify acids and bases?
- What happens when an acid reacts with a metal?
- Why is pH important for our body functions?
- How are salts different from acids and bases?
Key Concepts & Activities
1. Indicators and Identification
Types of acid-base indicators:
| Indicator | Color in Acid | Color in Base | Source/Type |
|---|---|---|---|
| Litmus | Red | Blue | Natural (lichen) |
| Phenolphthalein | Colorless | Pink | Synthetic |
| Methyl Orange | Red | Yellow | Synthetic |
| Turmeric | Yellow | Reddish-brown | Natural |
| China Rose | Dark pink | Green | Natural |
Activity 1: Prepare natural indicators from beetroot, red cabbage and test various household substances.
2. Chemical Properties
Reactions of acids and bases:
| Reaction Type | Acid Example | Base Example | Products |
|---|---|---|---|
| With Metals | Zn + HCl → | Zn + NaOH → | Salt + H2 gas |
| With Carbonates | Na2CO3 + HCl → | - | Salt + CO2 + H2O |
| With Each Other | HCl + NaOH → | NaOH + HCl → | Salt + H2O |
| With Metal Oxides | CuO + HCl → | - | Salt + H2O |
| With Non-metal Oxides | - | Ca(OH)2 + CO2 → | Salt + H2O |
Activity 2: Perform reactions of acids with metals, carbonates and bases; observe gas evolution and other changes.
3. pH Scale and Importance
pH values of common substances:
| Substance | pH Range | Nature | Importance |
|---|---|---|---|
| Gastric juice | 1.5-2.0 | Strongly acidic | Digestion |
| Lemon juice | 2.0-3.0 | Acidic | Food flavoring |
| Pure water | 7.0 | Neutral | Biological processes |
| Blood | 7.35-7.45 | Slightly basic | Critical for life |
| Soap solution | 9-10 | Basic | Cleaning agent |
Activity 3: Measure pH of various household substances using pH paper and universal indicator.
4. Salts and Their Uses
Common salts and applications:
| Salt | Chemical Formula | Preparation Method | Uses |
|---|---|---|---|
| Sodium chloride | NaCl | Neutralization/from sea | Food, industry |
| Washing soda | Na2CO3.10H2O | Recrystallization | Cleaning, glass |
| Baking soda | NaHCO3 | Solvay process | Baking, antacid |
| Bleaching powder | CaOCl2 | Chlorine + slaked lime | Disinfectant |
| Plaster of Paris | CaSO4.½H2O | Heating gypsum | Cast, molds |
Activity 4: Prepare common salts like copper sulfate crystals and study their water of crystallization.
Period Wise Plan
Total Duration: 6 Periods (45 minutes each)
Period 1: Introduction to Acids and Bases
Key Topics: Properties, indicators, everyday examples
Activities:
- Taste test (safe substances only)
- Indicator preparation and testing
- Classifying household substances
Resources: Litmus paper, turmeric, lemon juice, soap solution
Period 2: Chemical Reactions of Acids
Key Topics: Reactions with metals, carbonates, bases
Activities:
- Hydrogen gas test with metals
- Carbon dioxide test with carbonates
- Neutralization demonstration
Resources: Zinc granules, sodium carbonate, HCl, NaOH
Period 3: pH Scale and Importance
Key Topics: pH concept, measurement, biological importance
Activities:
- Measuring pH of various solutions
- Role-play of pH in digestion
- Case study on acid rain
Resources: pH paper, universal indicator, case studies
Period 4: Salts and Their Preparation
Key Topics: Types of salts, preparation methods, water of crystallization
Activities:
- Crystallization of copper sulfate
- Comparing hydrated and anhydrous salts
- Preparing common salts
Resources: Copper sulfate, washing soda, plaster of Paris
Period 5: Applications of Salts
Key Topics: Bleaching powder, baking soda, plaster of Paris
Activities:
- Bleaching action demonstration
- Baking soda volcano experiment
- Making casts with plaster
Resources: Bleaching powder, vinegar, plaster molds
Period 6: Review & Assessment
Key Topics: Comprehensive review, concept clarification
Activities:
- Concept mapping
- Practical assessment
- Written test
Resources: Assessment sheets, concept maps
Teaching Strategies
Assessment Timeline
Formative: Ongoing through periods 1-5 (lab reports, quizzes, participation)
Summative: Period 6 (comprehensive test, practical evaluation)
Assessment
Formative Assessment
- Observation during practical activities
- Quick quizzes on chemical properties and pH
- Lab reports on salt preparation
- Participation in discussions and demonstrations
Summative Assessment
- Written exam covering all concepts
- Practical test on identification and reactions
- Project on everyday applications
- Presentation on importance of pH
Extended Learning
- Research project on industrial applications
- Field visit to water treatment plant
- Design challenge for natural indicators
- Debate on antacid effectiveness
Frequently Asked Questions
- Why do acids taste sour while bases taste bitter?
- Acids release hydrogen ions (H+) that stimulate sour taste receptors on our tongue. Bases release hydroxide ions (OH-) that activate bitter taste receptors, explaining their distinct tastes.
- How does litmus paper work as an indicator?
- Litmus contains dye molecules that change structure in acidic vs basic conditions. In acids, the molecules absorb light to appear red, while in bases they absorb different wavelengths to appear blue.
- Why doesn't dry HCl gas change litmus color?
- Dry HCl exists as molecules (HCl) that can't release H+ ions. Only in water does it ionize to form H+ and Cl- ions that can interact with indicators.
- What determines the strength of an acid or base?
- Strength depends on how completely the substance dissociates in water. Strong acids/bases dissociate completely (like HCl, NaOH), while weak ones only partially dissociate (like acetic acid, NH4OH).
- Why is plaster of Paris written with ½ water molecule?
- The formula CaSO4.½H2O indicates that two formula units share one water molecule in the crystal structure, hence the "half" water notation.
