๐งช Chemistry — General Chemistry
1. Matter
Chemistry is the branch of science that deals with the composition, structure, properties, and reactions of matter.
DEFINITION
- Anything which has mass and occupies space is matter
- Made up of small entities called atoms or molecules
- Entities attract each other through intermolecular forces
- Space between entities is called intermolecular space
CLASSIFICATION OF MATTER
- Physical classification: Solid, Liquid, Gas
- Chemical classification: Elements, Compounds, Mixtures
2. States of Matter
SOLID STATE
- Fixed shape and fixed volume
- Particles tightly packed; held in rigid positions
- Crystalline solids: Regular arrangement; sharp melting point (e.g., NaCl, Diamond)
- Amorphous solids: Irregular arrangement; no sharp melting point (e.g., Glass, Rubber, Plastic)
- Amorphous solids are also called supercooled liquids
LIQUID STATE
- Variable shape; fixed volume
- Particles loosely packed; free to move
- Compress only slightly
GASEOUS STATE
- Variable shape and volume
- Particles widely spaced
- Highly compressible
GAS LAWS
| Law | Relation | Constant |
|---|---|---|
| Boyle's Law | p ∝ 1/V | T |
| Charles' Law | V ∝ T | p |
| Gay-Lussac's Law | p ∝ T | V |
| Avogadro's Law | V ∝ n | T, p |
PLASMA & BEC
- Plasma: Super-energetic ionised gases; found in stars
- Bose-Einstein Condensate (BEC): Formed at extremely low temperatures
3. Interconversion of States
KEY PROCESSES
- Melting: Solid → Liquid (Melting point decreases with impurities)
- Boiling: Liquid → Gas (Boiling point increases with impurities)
- Vaporisation: Liquid → Gas at room temperature
- Condensation: Gas → Liquid
- Freezing: Liquid → Solid (Freezing point decreases with impurities)
- Sublimation: Solid → Gas directly (e.g., Camphor, Naphthalene, NH₄Cl)
KEY POINTS
- Latent heat: Heat absorbed without temperature change during change of state
- Boiling point of water: 100°C
- At high altitude, food cooks late due to lower boiling point
- In pressure cooker, food cooks early due to higher boiling point
- Ethylene glycol: Used as antifreeze
- Sea water remains liquid below 0°C due to dissolved salt
4. Substances
TYPES OF SUBSTANCES
- Deliquescent: Absorbs moisture and forms saturated solution (e.g., NaOH, KOH, CaCl₂)
- Hygroscopic: Forms hydrates but not saturated solution (e.g., Quick lime, Na₂CO₃)
- Efflorescent: Loses water of crystallisation (e.g., Na₂CO₃·10H₂O)
5. Elements, Compounds and Mixtures
ELEMENTS
- Simplest form of matter; cannot be split by chemical/physical methods
- 118 elements known (94 natural, 23 artificial)
- Classified as: Metals, Non-metals, Metalloids
COMPOUNDS
- Two or more elements combined in fixed ratio
- Cannot be separated by physical methods
- Properties different from constituent elements
- Fixed melting and boiling point
- Examples: Water, Ammonia, CO₂, Sugar
MIXTURES
- Two or more elements/compounds in any ratio
- Can be separated by physical methods
- Shows properties of constituents
- Homogeneous: Uniform composition (e.g., Sugar in water)
- Heterogeneous: Non-uniform composition (e.g., Sand in water)
6. Separation Techniques
COMMON METHODS
| Method | Use |
|---|---|
| Filtration | Separate insoluble solid from liquid |
| Crystallisation | Purify solids (e.g., Salt from sea water) |
| Evaporation | Separate volatile solvent from non-volatile solute |
| Centrifugation | Separate cream from milk |
| Sublimation | Separate sublimable substances (e.g., NH₄Cl from NaCl) |
| Distillation | Separate liquids with different boiling points |
| Fractional Distillation | Separate liquids with close boiling points |
| Chromatography | Separate mixtures, purify compounds |
REVERSE OSMOSIS
- Solvent moves from higher concentration to lower concentration
- Used for desalination of sea water
7. Solution
DEFINITION
- Homogeneous mixture of two or more substances
- Solvent: Component present in larger quantity
- Solute: Component present in smaller quantity
TYPES OF SOLUTIONS
- Unsaturated: More solute can be dissolved
- Saturated: No more solute can be dissolved
- Supersaturated: More solute than saturated solution
CONCENTRATION TERMS
| Term | Definition |
|---|---|
| Molarity (M) | Moles of solute per litre of solution |
| Molality (m) | Moles of solute per kg of solvent |
| Normality (N) | Gram equivalent mass per litre |
| ppm | 1 mg solute in 1 litre solvent |
SOLUBILITY
- Amount of solute dissolved in 100g solvent to form saturated solution
- Increases with temperature for most substances
- Decreases with temperature for CaO, CaCO₃, CaSO₄ (dissolution evolves heat)
- Solubility of gases decreases with temperature
8. Colloidal Solution
DEFINITION
- Heterogeneous system with particles of size 1 nm to 100 nm
- Dispersed phase: Substance dispersed
- Dispersion medium: Substance in which dispersed
- Shows Tyndall effect (scattering of light)
TYPES OF COLLOIDS
| Dispersed Phase | Dispersion Medium | Example |
|---|---|---|
| Liquid | Gas | Fog, clouds, mist |
| Solid | Gas | Smoke |
| Gas | Liquid | Shaving cream |
| Liquid | Liquid | Milk, face cream (Emulsion) |
| Solid | Liquid | Milk of magnesia (Sol) |
| Gas | Solid | Foam, pumice stone |
| Liquid | Solid | Jelly, cheese (Gel) |
COLLOIDS AROUND US
- Clouds: Aerosol of water droplets in air
- Blue sky: Scattering of light by dust/water particles
- Blood: Colloidal solution of albuminoid
- Delta formation: Coagulation of clay by electrolytes in sea water
EMULSIONS
- Both dispersed phase and dispersion medium are liquids
- Examples: Milk, Cod liver oil
Summary: General Chemistry at a Glance
| Topic | Key Point |
|---|---|
| States of Matter | Solid, Liquid, Gas, Plasma, BEC |
| Crystalline Solids | Sharp melting point; regular arrangement |
| Amorphous Solids | No sharp melting point; supercooled liquids |
| Sublimation | Solid → Gas directly (Camphor, Naphthalene) |
| Colloidal Size | 1 nm to 100 nm |
| Tyndall Effect | Scattering of light by colloidal particles |
KEY TAKEAWAYS FOR UPSC
- Matter: Anything with mass and volume
- Amorphous solids: Glass, rubber, plastic (supercooled liquids)
- Sublimation: Camphor, Naphthalene, NH₄Cl
- Deliquescent: NaOH, KOH, CaCl₂
- Hygroscopic: Quick lime, Na₂CO₃
- Efflorescent: Na₂CO₃·10H₂O
- Colloidal size: 1 nm to 100 nm
- Tyndall effect: Scattering of light
- Reverse osmosis: Desalination of sea water
- Solubility of gases: Decreases with temperature
High-Yield Interactive UPSC Quiz (Chemistry — General Chemistry)
Q1. Which of the following is an example of an amorphous solid?
Correct Answer: C. Glass is an amorphous solid (supercooled liquid) with no sharp melting point.
Q2. What is the size range of colloidal particles?
Correct Answer: B. Colloidal particles have size range of 1 nm to 100 nm.
Q3. Which substance undergoes sublimation?
Correct Answer: B. Camphor, naphthalene, and ammonium chloride undergo sublimation.
Q4. Which of the following is a deliquescent substance?
Correct Answer: B. NaOH, KOH, and CaCl₂ are deliquescent substances.
Q5. What is the Tyndall effect?
Correct Answer: B. Tyndall effect is the scattering of light by colloidal particles.
Q6. Which technique is used for desalination of sea water?
Correct Answer: B. Reverse osmosis is used for desalination of sea water.
Q7. What happens to the solubility of gases in water with increase in temperature?
Correct Answer: A. Solubility of gases in water decreases with increase in temperature.
Q8. Which of the following is an emulsion?
Correct Answer: B. Milk is an emulsion where both dispersed phase and dispersion medium are liquids.
Q9. What is the boiling point of water at sea level?
Correct Answer: B. The boiling point of water at sea level is 100°C.
Q10. Which law states that V ∝ T at constant pressure?
Correct Answer: B. Charles' Law states that volume is directly proportional to temperature at constant pressure.