Materials Around Us

Given: Observation of kitchen organisation of edibles.

Sample Answer (students may write their own observations):

In my kitchen, edibles are usually kept together without a fixed system — spices, grains, pulses, and snacks may all be on the same shelf.

A better sorting method could be:
- Group 1 – Grains and Pulses: Rice, wheat, dal, etc. (stored in large airtight containers)
- Group 2 – Spices and Condiments: Salt, turmeric, chilli powder, etc. (stored in small labelled jars)
- Group 3 – Liquids: Oil, vinegar, sauces (stored in bottles on a separate shelf)
- Group 4 – Snacks and Ready-to-eat items: Biscuits, namkeen, etc. (stored in sealed packets or boxes)
- Group 5 – Perishables: Vegetables, fruits, dairy (stored in the refrigerator)

This classification is based on the type of material, size, and storage requirement, making it easier to find items quickly and keep the kitchen organised.

Given: Scrambled words to be unscrambled and matched with properties.

Step 1 – Unscramble each word:
- (i) TREMAT → MATTER
- (ii) ULSBELO → SOLUBLE
- (iii) TNERPASNART → TRANSPARENT
- (iv) ERUSTL → LUSTRE

Step 2 – Match with properties:
- (i) MATTER → (b) Occupies space and has mass
- (ii) SOLUBLE → (d) Mixes completely in water
- (iii) TRANSPARENT → (a) Objects can be seen clearly through it
- (iv) LUSTRE → (c) Shiny surface

Final Answer:
(i) → (b), (ii) → (d), (iii) → (a), (iv) → (c)

Given: Containers used in shops and at home are usually transparent.

Concept: Transparent materials allow light to pass through them so that objects inside can be seen clearly.

Reasons:
1. Easy identification: When containers are transparent, we can see the contents inside without opening them. This saves time and effort.
2. Checking quantity: We can easily check how much of a material is left in the container without opening it.
3. Checking quality: We can observe the colour, texture, and condition of the stored material to check if it is still good to use.
4. Convenience in shops: Shopkeepers and customers can quickly identify the product, making buying and selling easier.

Conclusion: Transparent containers are preferred because they allow us to see the contents clearly, making storage and retrieval more convenient and efficient.

Given: Four statements to be evaluated as True or False.

Concepts used:
- Transparent: objects seen clearly through it; Translucent: objects seen but not clearly; Opaque: objects cannot be seen through it.
- Lustre: shiny surface, usually metals.
- Soluble: dissolves in water; Insoluble: does not dissolve.
- Matter: anything that occupies space and has mass.

(i) Wood is translucent while glass is opaque.
→ False [F]
Correction: Wood is opaque (you cannot see through it) while glass is transparent (you can see clearly through it).

(ii) Aluminium foil has lustre while an eraser does not.
→ True [T]
Aluminium is a metal and has a shiny (lustrous) surface. An eraser is made of rubber, which is non-lustrous.

(iii) Sugar dissolves in water whereas sawdust does not.
→ True [T]
Sugar is soluble in water and disappears on stirring. Sawdust is insoluble and remains floating or settles at the bottom.

(iv) An apple is a matter because it occupies no space and has mass.
→ False [F]
Correction: An apple is a matter because it occupies space and has mass. (Matter is defined as anything that occupies space and has mass.)

Given: Chairs can be made from wood, iron, plastic, bamboo, cement, and stones. We need to identify which material best fulfils each property.

(i) Hardness (does not bend or shake on sitting even after long use):
→ Iron, Cement, and Stone fulfil this property the most. These materials are very hard and rigid, so they do not bend or shake even after prolonged use.

(ii) Lightweight (easy to lift or to take from one place to another):
→ Plastic and Bamboo fulfil this property the most. They are light in weight and can be easily carried from one place to another.

(iii) Does not feel very cold when sitting during winters:
→ Wood, Bamboo, and Plastic fulfil this property the most. These materials do not conduct heat as readily as metals, so they do not feel very cold to the touch in winters. Iron, cement, and stone feel very cold in winter.

(iv) Can be cleaned regularly and made to look new even after long use:
→ Plastic fulfils this property the most. Plastic chairs can be wiped clean easily, do not rust, and retain their appearance for a long time. Wood can also be polished to look new.

Given: Containers are needed for food waste, broken glass, and wastepaper.

We need to consider properties such as hardness, durability, ability to be cleaned, safety, and weight.

(i) Food waste:
→ Material chosen: Plastic or metal (steel/aluminium)
- Properties to consider: Should be waterproof (food waste may be wet), easy to clean (to prevent smell and germs), durable, and should have a lid to prevent smell from spreading. Plastic is lightweight and easy to clean; metal is more durable.

(ii) Broken glass:
→ Material chosen: Thick metal (steel or iron) or hard, thick plastic
- Properties to consider: The container must be hard and sturdy so that sharp glass pieces do not pierce through it. It should be rigid and not easily breakable. A soft or thin container (like a paper bag) would be dangerous as glass pieces could cut through it.

(iii) Wastepaper:
→ Material chosen: Cardboard box or plastic bin
- Properties to consider: Should be lightweight (paper is not very heavy), large enough to hold paper, and easy to empty. Since paper is dry, the container does not need to be waterproof. A cardboard box or a simple plastic bin works well.

Conclusion: The choice of material for a container depends on the nature of the waste — whether it is wet or dry, sharp or soft, heavy or light.

Given: Air allows us to see through it clearly; a wooden door does not allow us to see through it at all.

Concept:
- Transparent materials allow light to pass through completely, so objects can be seen clearly through them (e.g., air, clear glass).
- Opaque materials do not allow light to pass through them at all, so objects cannot be seen through them (e.g., wood, metal).

Since air allows us to see each other clearly → air is transparent.
Since a wooden door does not allow us to see through it → wood is opaque.

Correct Answer: Option (i) — transparent, opaque

Given:
- Material X: rigid, does not change shape easily; dissolves completely in water.
- Material Y: easily changes shape when pressed; does not dissolve in water.

Identifying Material X:
- It is hard (rigid, does not change shape easily).
- It is soluble in water (dissolves completely).
- A material that is hard and soluble in water could be sugar or salt (common salt/sodium chloride).
- Both sugar and salt are hard crystalline solids that dissolve completely in water.

Identifying Material Y:
- It is soft (easily changes shape when pressed).
- It is insoluble in water (remains unchanged).
- A material that is soft and insoluble in water could be rubber, clay, wax, or sponge.
- For example, clay is soft and does not dissolve in water; rubber is soft and insoluble in water.

Conclusion:
- Material X is hard because it is rigid and resists compression or change in shape. (e.g., sugar or salt)
- Material Y is soft because it easily changes its shape when pressed. (e.g., rubber or clay)

Justification: Hardness and softness are properties related to how easily a material can be compressed or scratched. Solubility is a separate property related to how a material behaves in water. Material X is hard yet soluble, while Material Y is soft yet insoluble — showing that hardness and solubility are independent properties.

Given: Five clues describing five different materials. Each clue describes a different material.

(a) I have lustre.
→ I am a metal (such as iron, copper, aluminium, or gold).
Metals have shiny surfaces and are said to be lustrous.

(b) I can be easily compressed.
→ I am a soft material such as sponge, cotton, or rubber.
Soft materials can be easily compressed or change shape when pressed.

(c) I am hard and soluble in water.
→ I am sugar or salt (common salt).
Both are hard crystalline solids that dissolve completely in water.

(d) You cannot see clearly through me.
→ I am a translucent material such as butter paper or frosted glass.
Translucent materials allow some light to pass through but objects cannot be seen clearly through them.

(e) I have mass and volume but you cannot see me.
→ I am air (or any gas).
Air is matter — it has mass and occupies space (volume) — but it is invisible to the naked eye.

Given: Students are asked to create their own 'Who am I?' riddle based on properties of materials.

Sample 'Who am I?' created by a student:

(a) I am non-lustrous (I do not have a shiny surface).
(b) I am opaque — you cannot see through me at all.
(c) I am hard and cannot be easily compressed or scratched.
(d) I am insoluble in water.
(e) I am used to make furniture, doors, and pencils.

Answer: I am WOOD.

*(Students may create their own riddles for materials like glass, iron, rubber, plastic, etc., using properties such as lustre, hardness, transparency, solubility, mass, and volume.)*

Given materials: vinegar, honey, mustard oil, water, glucose, wheat flour.

Concept: Soluble materials dissolve completely in a solvent (like water); insoluble materials do not dissolve and remain as a separate layer or settle down.

Two pairs where one material is SOLUBLE in the other:

1. Glucose + Water: Glucose (a type of sugar) dissolves completely in water when stirred. → Glucose is soluble in water.

2. Honey + Water: Honey mixes completely with water when stirred. → Honey is soluble in water.

*(Vinegar also mixes with water, so vinegar + water is another valid pair.)*

Two pairs where one material is INSOLUBLE in the other:

1. Mustard oil + Water: Mustard oil does not dissolve in water. It forms a separate layer on top of water when left undisturbed. → Mustard oil is insoluble in water.

2. Wheat flour + Water: Wheat flour does not dissolve in water; it forms a suspension (cloudy mixture) and the particles settle at the bottom after some time. → Wheat flour is insoluble in water.

Summary Table:

| Pair | Soluble / Insoluble |
|---|---|
| Glucose + Water | Soluble |
| Honey + Water | Soluble |
| Mustard oil + Water | Insoluble |
| Wheat flour + Water | Insoluble |