Topic Overview
🔬 Chapter Overview: Materials & Chemical Changes
This chapter is a favorite for AP TET as it covers the fundamentals of chemistry in our daily lives. We will explore why materials are different, how to separate them, and the crucial differences between acids, bases, and the changes materials undergo (like rusting).
1. Properties & Classification of Materials
We classify objects based on their properties. These properties determine what we use them for.
Key Properties
- Luster: Shininess. Metals are lustrous; non-metals are dull.
- Hardness: Resistance to scratching. Diamond is the hardest; chalk is soft.
- Conduction: Ability to allow heat or electricity to pass through. Metals are good conductors; wood/plastic are insulators.
- Transparency: How much light can pass through.
TRANSPARENCY CLASSIFICATION
| Type | Property | Example |
|---|---|---|
| Transparent | Allows all light to pass; can see clearly. | Glass, Clean Water |
| Translucent | Allows some light to pass; see blurry images. | Butter Paper, Frosted Glass |
| Opaque | Blocks all light; cannot see through. | Wood, Brick, Metal |
🌍 Real-Life Application: A cooking pan has two parts. The base is made of metal (a conductor) to quickly transfer heat to the food. The handle is made of plastic or wood (insulators) so we can hold it without getting burned.
2. Metals, Non-metals & Reactivity
Materials are broadly classified as metals and non-metals based on their physical and chemical properties.
COMPARISON: METALS vs. NON-METALS
| Property | Metals | Non-Metals |
|---|---|---|
| Luster | Lustrous (Shiny) | Dull (Not shiny) |
| State | Solid (except Mercury) | Solid, Liquid, or Gas |
| Malleability | High (can be beaten into sheets) | Low (Brittle, breaks if beaten) |
| Ductility | High (can be drawn into wires) | Low (Not ductile) |
| Conduction | Good conductors of heat & electricity | Poor conductors (Insulators) |
| Sonority | Sonorous (make a ringing sound) | Non-sonorous |
⚠️ Exam-Focus: The Exceptions!
- Mercury (Hg): A metal that is liquid at room temperature.
- Graphite (Carbon): A non-metal that conducts electricity.
- Iodine (I): A non-metal that is lustrous (shiny).
- Sodium (Na) & Potassium (K): Metals that are soft and can be cut with a knife.
Reactivity Order of Metals
This series shows which metals are “stronger” (more reactive). A more reactive metal will displace a less reactive one from its salt solution.
Most Reactive → Least Reactive
K (Potassium) > Na (Sodium) > Mg (Magnesium) > Al (Aluminum) > Zn (Zinc) > Fe (Iron) > Cu (Copper) > Ag (Silver) > Au (Gold)
🌍 Real-Life Application (Displacement): If you place an iron nail (Fe) in a blue copper sulphate solution (CuSO₄), the solution slowly turns green. Why? Iron is MORE reactive, so it “kicks out” the copper.
Fe + CuSO₄ → FeSO₄ + Cu (Iron + Copper Sulphate → Iron Sulphate + Copper)
Fe + CuSO₄ → FeSO₄ + Cu (Iron + Copper Sulphate → Iron Sulphate + Copper)
🧠 Memory Shortcut (Reactivity): Remember “Please Stop Calling Me A Zebra, I Like Calling Silver Gold.”
(K, Na, Ca, Mg, Al, Zn, Fe, Pb, Cu, Ag, Au)
(K, Na, Ca, Mg, Al, Zn, Fe, Pb, Cu, Ag, Au)
3. Methods of Separation (Mixtures)
Most things in nature are mixtures. We use separation techniques based on the different properties of the components.
| Method | Type of Mixture | Example |
|---|---|---|
| Handpicking / Sieving | Solid + Solid (different size/color) | Removing stones from rice; separating pebbles from sand. |
| Winnowing | Solid + Solid (heavy + light) | Separating husk (light) from grain (heavy) using wind. |
| Filtration | Insoluble Solid + Liquid | Separating mud from water; making tea (separating leaves). |
| Evaporation | Soluble Solid + Liquid | Getting salt from seawater (water evaporates, salt remains). |
| Sublimation | Solid + Solid (one sublimes) | Separating camphor (sublimes) from salt. |
| Chromatography | Colors in a liquid | Separating the different colors in black ink. |
🌍 Real-Life Application: When we make tea, we use filtration to separate the (insoluble) tea leaves from the liquid tea. If you wanted to get the sugar *back* from the sweet tea, you would have to use evaporation.
4. Saturated and Unsaturated Solutions
- Solute: The substance that is dissolved (e.g., Sugar).
- Solvent: The substance that does the dissolving (e.g., Water).
- Solution: The uniform mixture (e.g., Sugar Water).
Saturated vs. Unsaturated
Unsaturated: A solution that can still dissolve more solute.
Saturated: A solution that cannot dissolve any more solute at a given temperature. It is “full”.
💡 Concept Highlight: Effect of Temperature
- Solids (like Sugar): Solubility increases as temperature increases. You can dissolve more sugar in hot water than in cold.
- Gases (like CO₂): Solubility decreases as temperature increases. A warm soda goes “flat” faster because the gas escapes.
🌍 Real-Life Application: A cool drink (soda) is a solution of CO₂ gas (solute) dissolved in water (solvent). When you open the warm bottle, the gas quickly escapes (low solubility), and it goes flat. This is why sodas are “Best Served Chilled”.
5. Acids, Bases, and Salts
Substances are classified as acidic, basic, or neutral.
COMPARISON: ACIDS vs. BASES
| Property | Acids | Bases |
|---|---|---|
| Taste | Sour | Bitter |
| Feel | Often watery | Soapy / Slippery |
| Litmus Test | Turns Blue Litmus Red (BRA) | Turns Red Litmus Blue (RRB) |
| Examples | Lemon Juice (Citric Acid), Vinegar (Acetic Acid) | Soap, Baking Soda, Antacid tablets |
Indicators
Indicators are special substances that change color to show if a substance is acidic or basic.
- Litmus (Natural): Most common. (See table).
- Turmeric (Natural): Stays yellow in acid; turns reddish-brown in base (like on a curry stain with soap).
- Phenolphthalein (Synthetic): Stays colorless in acid; turns pink in base.
Neutralization
When an acid and a base react, they cancel each other out (neutralize) to form a salt and water. This reaction often produces heat.
Acid + Base → Salt + Water
HCl + NaOH → NaCl + H₂O
HCl + NaOH → NaCl + H₂O
🌍 Real-Life Application:
1. Indigestion: We take an Antacid (a base) to neutralize excess
stomach acid.
2. Ant Sting: An ant injects Formic Acid. We treat it with Baking Soda (a base) to neutralize it.
1. Indigestion: We take an Antacid (a base) to neutralize excess
stomach acid.
2. Ant Sting: An ant injects Formic Acid. We treat it with Baking Soda (a base) to neutralize it.
6. Physical & Chemical Changes
Materials around us are always changing. We group these changes into two types.
COMPARISON: PHYSICAL vs. CHEMICAL CHANGE
| Feature | Physical Change | Chemical Change |
|---|---|---|
| New Substance? | No new substance is formed. | Yes, one or more new substances are formed. |
| Reversible? | Usually reversible. | Usually irreversible. |
| Examples | Melting ice, boiling water, tearing paper, dissolving sugar. | Burning wood, rusting of iron, cooking an egg, souring of milk. |
🌍 Real-Life Application (Both): A burning candle shows both changes.
- Physical Change: The wax melts (solid → liquid). This is reversible.
- Chemical Change: The hot wax vapor burns (reacts with oxygen) to produce light, heat, CO₂, and water. This is irreversible.
Key Chemical Changes
- Rusting of Iron: This is a slow chemical change that requires both Oxygen AND Water. Rust is a new substance (hydrated iron oxide).
- Galvanization: A method to prevent rusting by coating iron with a layer of Zinc (Zn).
- Crystallization: This is a physical change used for purification (like making sugar crystals from sugar syrup).
📝 AP TET Exam Tips & Sample Questions
Chemistry Memory Formula Sheet
- Neutralization: Acid + Base → Salt + Water
- Rusting: Iron + Oxygen (O₂) + Water (H₂O) → Rust
- Galvanization: Coating Iron with Zinc (Zn)
- Litmus Test: Acid = BRA (Blue → Red); Base = RRB (Red → Blue)
- Metal Oxide + Water → Base (e.g., MgO)
- Non-metal Oxide + Water → Acid (e.g., SO₂)
Sample AP TET Questions
- Which of the following is a chemical change?
A) Melting of ice B) Dissolving salt in water C) Rusting of an iron nail D) Tearing a piece of paper
Answer: C (Rust is a new substance) - A student tests a clear liquid with red litmus paper, and it turns blue. The liquid is:
A) An acid B) A base C) Neutral D) Water
Answer: B (Bases turn red litmus blue) - The process of coating iron with a layer of zinc to prevent rusting is called:
A) Crystallization B) Galvanization C) Evaporation D) Neutralization
Answer: B
🚀 Speed Tip: For “Physical vs. Chemical” questions, ask yourself one thing: “Is this a new substance, or just the same substance in a new shape/state?” If it’s new (ash, rust, cooked egg), it’s **chemical**. If it’s the same (ice/water, torn paper, salt/water), it’s **physical**.