MATTER IN OUR SURROUNDINGS - Q&A
Questions Page 3
1. Which of the following are matter?
Chair, air, love, smell, hate, almonds, thought, cold, lemon water, smell of perfume.
Matter is anything that occupies space and has mass.
The following items from the list are matter:
Chair, air, almonds, lemon water, smell of perfume (because it consists of matter particles diffusing in the air).
The following are not matter (they are feelings, sensations, or abstract concepts):
Love, smell (the sense itself), hate, thought, cold.
2. Give reasons for the following observation:
The smell of hot sizzling food reaches you several metres away, but to get the smell from cold food you have to go close.
This happens due to the process of diffusion. At higher temperatures, the kinetic energy of the particles increases, causing them to move much faster. The particles of aroma from hot sizzling food diffuse rapidly into the air and reach us even at a distance. In contrast, the particles of cold food have low kinetic energy and move slowly, so they do not diffuse far, requiring us to go close to smell them.
3. A diver is able to cut through water in a swimming pool. Which property of matter does this observation show?
This observation shows the following properties of matter:
1. The particles of matter (water) have spaces between them.
2. The forces of attraction between the particles of liquid (water) are not very strong, allowing the diver to displace the water and pass through it.
4. What are the characteristics of the particles of matter?
The main characteristics of particles of matter are:
1. Particles of matter have spaces between them.
2. Particles of matter are continuously moving (they possess kinetic energy).
3. Particles of matter attract each other.
Questions Page 6
1. The mass per unit volume of a substance is called density. (density = mass/volume).
Arrange the following in order of increasing density – air, exhaust from chimneys, honey, water, chalk, cotton and iron.
The order of increasing density is:
Air < Exhaust from chimneys < Cotton < Water < Honey < Chalk < Iron.
Explanation: Gases (Air, Exhaust) have the lowest density. Solids like Cotton have low density due to trapped air (porous). Liquids (Water, Honey) are denser, with Honey being denser than Water. Solids (Chalk, Iron) are generally the densest.
2. (a) Tabulate the differences in the characteristics of states of matter.
| Property | Solid | Liquid | Gas |
|---|---|---|---|
| Shape | Definite shape | No definite shape (takes shape of container) | No definite shape |
| Volume | Definite volume | Definite volume | No definite volume |
| Intermolecular Space | Very small (tightly packed) | Moderate (loosely packed) | Very large (free to move) |
| Force of Attraction | Very strong | Moderate (weaker than solids) | Negligible |
| Compressibility | Negligible | Low | High |
(b) Comment upon the following: rigidity, compressibility, fluidity, filling a gas container, shape, kinetic energy and density.
Rigidity: The tendency of a substance to maintain its shape when subjected to outside force. Solids are rigid.
Compressibility: The property of being reduced in volume under pressure. Gases are highly compressible.
Fluidity: The ability to flow. Liquids and gases are fluids.
Filling a gas container: A gas fills a container completely because its particles move randomly at high speeds in all directions.
Shape: Solids have a fixed shape. Liquids and gases do not have a fixed shape.
Kinetic Energy: The energy possessed by particles due to their motion. Gases have the maximum kinetic energy, followed by liquids, and solids have the least.
Density: Mass per unit volume. Solids usually have high density, while gases have low density.
3. Give reasons
(a) A gas fills completely the vessel in which it is kept.
(b) A gas exerts pressure on the walls of the container.
(c) A wooden table should be called a solid.
(d) We can easily move our hand in air but to do the same through a solid block of wood we need a karate expert.
(a) The particles of a gas have negligible force of attraction and high kinetic energy. They move randomly in all directions at high speeds, thus filling the entire available space of the vessel.
(b) The gas particles move randomly and hit each other and the walls of the container with force. This force exerted by gas particles per unit area on the walls creates pressure.
(c) A wooden table has a definite shape, a definite volume, is rigid, and cannot be compressed. These are characteristics of a solid, so it is called a solid.
(d) In air, the particles are far apart and the force of attraction is very weak, making it easy to break through them. In a solid block of wood, the particles are tightly packed with very strong forces of attraction. To break these forces and move a hand through, a large amount of force is required (like that of a karate expert).
4. Liquids generally have lower density as compared to solids. But you must have observed that ice floats on water. Find out why.
Although ice is a solid, it floats on water because its density is lower than that of liquid water. This happens because the structure of ice creates a cage-like arrangement with vacant spaces between the water molecules. This makes the volume of ice larger than the same mass of water, resulting in lower density.
Questions Page 9
1. Convert the following temperature to celsius scale:
a. 300 K
b. 573 K
The formula to convert Kelvin to Celsius is: T(°C) = T(K) - 273
a. 300 K = 300 - 273 = 27°C
b. 573 K = 573 - 273 = 300°C
2. What is the physical state of water at:
a. 250°C
b. 100°C?
a. At 250°C: Since the boiling point of water is 100°C, at 250°C water exists in the gaseous state (steam).
b. At 100°C: This is the boiling point of water. At this temperature, water can exist in both the liquid state and the gaseous state (as steam), as the phase change occurs here.
3. For any substance, why does the temperature remain constant during the change of state?
During a change of state (like melting or boiling), the heat energy supplied is used up in overcoming the forces of attraction between the particles to change their state, rather than increasing the kinetic energy (temperature) of the particles. This heat is known as latent heat. Therefore, the temperature remains constant until the entire substance has changed state.
4. Suggest a method to liquefy atmospheric gases.
Atmospheric gases can be liquefied by:
1. Increasing the pressure: This brings particles closer together.
2. Decreasing the temperature: This reduces the kinetic energy of the particles.
So, applying high pressure and lowering the temperature is the method to liquefy gases.
Questions Page 10
1. Why does a desert cooler cool better on a hot dry day?
A desert cooler works on the principle of evaporation. On a hot, dry day, the temperature is high and the humidity (moisture in air) is low. These conditions increase the rate of evaporation of water. Since evaporation causes cooling (by absorbing latent heat from the surroundings), the cooler works more effectively.
2. How does the water kept in an earthen pot (matka) become cool during summer?
An earthen pot has many microscopic pores in its walls. Water seeps out through these pores to the surface and evaporates. The energy required for evaporation (latent heat of vaporization) is taken from the water inside the pot and the pot itself. This loss of heat makes the remaining water cool.
3. Why does our palm feel cold when we put some acetone or petrol or perfume on it?
Acetone, petrol, and perfume are volatile liquids (they evaporate quickly). When put on the palm, they absorb the heat energy required for evaporation from the palm or the surroundings. This loss of heat causes the palm to feel cold.
4. Why are we able to sip hot tea or milk faster from a saucer rather than a cup?
A saucer provides a larger surface area than a cup. Evaporation is a surface phenomenon; a larger surface area increases the rate of evaporation. Faster evaporation causes faster cooling of the tea or milk, allowing us to sip it more quickly.
5. What type of clothes should we wear in summer?
We should wear cotton clothes in summer. During summer, we sweat more. Cotton is a good absorber of water, so it absorbs the sweat from our body and exposes it to the atmosphere for easy evaporation. As the sweat evaporates, it absorbs heat from the body, keeping us cool and comfortable.
Exercises
1. Convert the following temperatures to the celsius scale.
(a) 293 K (b) 470 K
Formula: °C = K - 273
(a) 293 K = 293 - 273 = 20°C
(b) 470 K = 470 - 273 = 197°C
2. Convert the following temperatures to the kelvin scale.
(a) 25°C (b) 373°C
Formula: K = °C + 273
(a) 25°C = 25 + 273 = 298 K
(b) 373°C = 373 + 273 = 646 K
3. Give reason for the following observations.
(a) Naphthalene balls disappear with time without leaving any solid.
(b) We can get the smell of perfume sitting several metres away.
(a) Naphthalene undergoes sublimation, a process where a solid changes directly into a gas without becoming a liquid. Therefore, the balls keep forming vapors over time and eventually disappear without leaving any residue.
(b) Perfume contains volatile solvents that turn into gas vapor quickly. These gas particles move at high speeds and diffuse (mix) into the air particles rapidly, carrying the smell to us even several meters away.
4. Arrange the following substances in increasing order of forces of attraction between the particles— water, sugar, oxygen.
The force of attraction is weakest in gases, stronger in liquids, and strongest in solids.
Oxygen (Gas) < Water (Liquid) < Sugar (Solid)
Order: Oxygen < Water < Sugar
5. What is the physical state of water at—
(a) 25°C (b) 0°C (c) 100°C ?
(a) 25°C: Liquid state (Room temperature).
(b) 0°C: Solid state (Ice) or Liquid state (Water). This is the freezing/melting point where both phases can coexist.
(c) 100°C: Liquid state (Water) or Gaseous state (Steam). This is the boiling point where both phases can coexist.
6. Give two reasons to justify—
(a) water at room temperature is a liquid.
(b) an iron almirah is a solid at room temperature.
(a) Water is a liquid at room temperature because:
1. It has a definite volume but no definite shape (it takes the shape of the container).
2. It flows (has fluidity).
(b) An iron almirah is a solid because:
1. It has a fixed shape and a fixed volume.
2. It is rigid and cannot be compressed.
7. Why is ice at 273 K more effective in cooling than water at the same temperature?
Ice at 273 K (0°C) absorbs latent heat of fusion from the substance it is cooling to melt into water. Water at 273 K has already absorbed this heat. Therefore, ice absorbs more heat energy from the surroundings than water at the same temperature, causing more effective cooling.
8. What produces more severe burns, boiling water or steam?
Steam produces more severe burns. This is because particles in steam at 373 K (100°C) have absorbed extra energy in the form of latent heat of vaporization compared to boiling water at the same temperature. When steam touches skin, it releases this massive amount of extra heat, causing worse burns.
9. Name A,B,C,D,E and F in the following diagram showing change in its state
A: Fusion (or Melting) — Solid to Liquid
B: Vaporisation — Liquid to Gas
C: Condensation — Gas to Liquid
D: Solidification — Liquid to Solid
E: Sublimation — Solid to Gas (Increase heat, decrease pressure)
F: Deposition (or Sublimation) — Gas to Solid (Decrease heat, increase pressure)