Comprehensive Notes on Matter in Our Surroundings

Matter in Our Surroundings

Introduction

• Everything in the universe is made up of "matter." Scientists define matter as any material that occupies space and has mass. Examples include air, food, stones, clouds, stars, plants, animals, water droplets, and sand particles.
• Early Indian philosophers classified matter into five basic elements called "Panch Tatva": air, earth, fire, sky, and water. They believed all living and non-living things were composed of these elements.
• Ancient Greek philosophers had a similar classification of matter.
• Modern scientists classify matter based on physical properties and chemical nature. This chapter focuses on the physical properties of matter. Chemical aspects will be discussed later.

1.1 Physical Nature of Matter

1.1.1 Matter is Made Up of Particles

• Two schools of thought existed regarding the nature of matter:
  • One believed matter was continuous, like a block of wood.
  • The other believed matter was made up of particles, like sand.

Activity 1.1: Deciding the Nature of Matter
* Take a 100 mL beaker.
* Fill half the beaker with water and mark the water level.
* Dissolve some salt/sugar with a glass rod.
* Observe any change in water level.
* The salt or sugar spreads throughout the water to answer that matter is made up of particles.

1.1.2 How Small Are These Particles of Matter?

Activity 1.2: Estimating the Size of Matter Particles
* Take 2-3 crystals of potassium permanganate and dissolve them in 100 mL of water.
* Take out approximately 10 mL of this solution and put it into 90 mL of clear water.
* Repeat the dilution process 5 to 8 times.
* Observe that the water is still colored, indicating that a few crystals of potassium permanganate can color a large volume of water (about 1000 L).
* This suggests that there are millions of tiny particles in just one crystal of potassium permanganate, which keep dividing into smaller particles.
* The same activity can be done using 2 mL of Dettol instead of potassium permanganate to detect the smell even on repeated dilution.
* Particles of matter are very small, beyond our imagination.

1.2 Characteristics of Particles of Matter

1.2.1 Particles of Matter Have Space Between Them

• In Activities 1.1 and 1.2, sugar, salt, Dettol, and potassium permanganate distribute evenly in water.
• Similarly, when making tea, coffee, or lemonade, particles of one type of matter get into the spaces between particles of the other.
• This shows that there is enough space between particles of matter.

1.2.2 Particles of Matter Are Continuously Moving

Activity 1.3: Observing Movement of Particles
* Put an unlit incense stick in a corner of the class and note how close one must go to smell it.
* Light the incense stick and observe if the smell can be detected from a distance.

Activity 1.4: Observing Diffusion
* Take two glasses/beakers filled with water.
* Put a drop of blue or red ink slowly along the sides of the first beaker and honey in the same way in the second beaker.
* Leave them undisturbed and record observations.
* Note the immediate observations after adding ink and honey.
* Observe how many hours or days it takes for the color of ink to spread evenly throughout the water.

Activity 1.5: Effect of Temperature on Mixing
* Drop a crystal of copper sulfate or potassium permanganate into a glass of hot water and another containing cold water without stirring.
* Observe the area just above the solid crystal in the glass.
* Observe changes over time.
* Determine what this suggests about the particles of solid and liquid.
* Note if the rate of mixing changes with temperature and why.

• From the activities above, we observe that particles of matter are continuously moving, possessing kinetic energy. As temperature increases, particles move faster, implying that kinetic energy increases with temperature.
• Particles of matter intermix on their own by getting into the spaces between the particles. This intermixing of particles of two different types of matter on their own is called diffusion. Diffusion becomes faster on heating because particles move faster.

1.2.3 Particles of Matter Attract Each Other

Activity 1.6: Demonstrating Interparticle Attraction Through a Game
* Make four groups to form human chains:
* The first group should hold each other from the back and lock arms.
* The second group should hold hands.
* The third group should form a chain by touching each other with only their finger tips.
* The fourth group of students should run around and try to break the three human chains into as many small groups as possible.
* Observe which group was the easiest to break and why. This illustrates the varying forces of attraction between particles.

Activity 1.7: Breaking Substances
* Take an iron nail, a piece of chalk, and a rubber band.
* Try breaking them by hammering, cutting, or stretching.
* Determine which of the three substances has particles held together with greater force.

Activity 1.8: Cutting the Surface of Water
* Take some water in a container and try cutting the surface of water with fingers.
* Note if it's possible to cut the surface of water.
* Consider the reason behind the surface of water remaining together.

• These activities suggest that particles of matter have a force acting between them, keeping the particles together. The strength of this force of attraction varies from one kind of matter to another.

1.3 States of Matter

• Matter exists in three different states: solid, liquid, and gas. These states arise due to the variation in the characteristics of the particles of matter.

1.3.1 The Solid State

Activity 1.9: Observing Solids
* Collect a pen, a book, a needle, and a piece of wooden stick.
* Sketch the shape of the above articles in a notebook by moving a pencil around them.
* Check if all these have a definite shape, distinct boundaries, and a fixed volume.
* Hammer, pull, or drop them to note what happens.
* Try to compress them by applying force.

• All the above are examples of solids. We can observe that all these have a definite shape, distinct boundaries, and fixed volumes, showing negligible compressibility.
• Solids have a tendency to maintain their shape when subjected to outside force. Solids may break under force, but it is difficult to change their shape, so they are rigid.
• Consider the following:
  • (a) A rubber band changes its shape on stretching but regains the same shape when the force is removed. If excessive force is applied, it breaks, however, it's considered a solid.
  • (b) Sugar and salt when kept in different jars take the shape of the jar, however, the shape of each individual sugar or salt crystal remains fixed, whether we take it in our hand, put it in a plate or in a jar, thus they are solid.
  • (c) A sponge has minute holes in which air is trapped. When we press it, the air is expelled out, and we are able to compress it, but the sponge is a solid.

1.3.2 The Liquid State

Activity 1.10: Observing Liquids
* Collect water, cooking oil, milk, juice, and a cold drink.
* Collect containers of different shapes and put a 50 mL mark on these containers using a measuring cylinder from the laboratory.
* Note what will happen if these liquids are spilt on the floor.
* Measure 50 mL of any one liquid and transfer it into different containers one by one. Check if the volume remains the same.
* Check if the shape of the liquid remains the same.
* When you pour the liquid from one container into another, check if it flows easily.

• We observe that liquids have no fixed shape but have a fixed volume. They take up the shape of the container in which they are kept.
• Liquids flow and change shape, so they are not rigid but can be called fluid.
• Solids and liquids can diffuse into liquids. Gases from the atmosphere diffuse and dissolve in water. These gases, especially oxygen and carbon dioxide, are essential for the survival of aquatic animals and plants. All living creatures need to breathe for survival. The aquatic animals can breathe underwater due to the presence of dissolved oxygen in water.
• Thus, we may conclude that solids, liquids, and gases can diffuse into liquids. The rate of diffusion of liquids is higher than that of solids. This is due to the fact that in the liquid state, particles move freely and have greater space between each other as compared to particles in the solid state.

1.3.3 The Gaseous State

Activity 1.11: Compressibility of Matter
* Take three 100 mL syringes and close their nozzles by rubber corks.
* Remove the pistons from all the syringes.
* Leaving one syringe untouched, fill water in the second and pieces of chalk in the third.
* Insert the pistons back into the syringes. You may apply some vaseline on the pistons before inserting them into the syringes for their smooth movement.
* Now, try to compress the content by pushing the piston in each syringe.

• We have observed that gases are highly compressible as compared to solids and liquids. The liquefied petroleum gas (LPG) cylinder that we get in our home for cooking or the oxygen supplied to hospitals in cylinders is compressed gas. Compressed natural gas (CNG) is used as fuel these days in vehicles. Due to its high compressibility, large volumes of gas can be compressed into a small cylinder and transported easily.
• The particles of the aroma of food mix with the particles of air spread from the kitchen, reach us, and even farther away. The smell of hot cooked food reaches us in seconds compared to the rate of diffusion of solids and liquids. Due to the high speed of particles and large space between them, gases show the property of diffusing very fast into other gases.
• In the gaseous state, the particles move about randomly at high speed. Due to this random movement, the particles hit each other and also the walls of the container. The pressure exerted by the gas is because of this force exerted by gas particles per unit area on the walls of the container.

1.4 Can Matter Change its State?

• Water can exist in three states of matter: solid (ice), liquid (water), and gas (water vapor).

1.4.1 Effect of Change of Temperature

Activity 1.12: Effect of Heating on Matter
* Take about 150 g of ice in a beaker and suspend a laboratory thermometer so that its bulb is in contact with the ice.
* Start heating the beaker on a low flame.
* Note the temperature when the ice starts melting.
* Note the temperature when all the ice has converted into water.
* Record observations for the conversion of solid to liquid state.
* Now, put a glass rod in the beaker and heat while stirring till the water starts boiling.
* Keep a careful eye on the thermometer reading till most of the water has vaporized.
* Record observations for the conversion of water in the liquid state to the gaseous state.

• On increasing the temperature of solids, the kinetic energy of the particles increases. Due to the increase in kinetic energy, the particles start vibrating with greater speed. The energy supplied by heat overcomes the forces of attraction between the particles. The particles leave their fixed positions and start moving more freely. A stage is reached when the solid melts and is converted to a liquid.
• The minimum temperature at which a solid melts to become a liquid at the atmospheric pressure is called its melting point. The melting point of a solid indicates the strength of the force of attraction between its particles. The melting point of ice is $273.15 K$. The process of melting, that is, the change of solid-state into the liquid state is also known as fusion.
• When a solid melts, its temperature remains the same, even though we continue to heat the beaker, that is, we continue to supply heat. This heat gets used up in changing the state by overcoming the forces of attraction between the particles. As this heat energy is absorbed by ice without showing any rise in temperature, it is considered that it gets hidden into the contents of the beaker and is known as latent heat. The word latent means hidden.
• The amount of heat energy required to change 1 kg of a solid into a liquid at atmospheric pressure at its melting point is known as the latent heat of fusion. So, particles in water at $0^\circ C$ ($273 K$) have more energy compared to particles in ice at the same temperature.
• When we supply heat energy to water, particles start moving even faster. At a certain temperature, a point is reached when the particles have enough energy to break free from the forces of attraction of each other. At this temperature, the liquid starts changing into gas.
• The temperature at which a liquid starts boiling at atmospheric pressure is known as its boiling point. Boiling is a bulk phenomenon. Particles from the bulk of the liquid gain enough energy to change into the vapor state. For water, this temperature is $373 K$ ($100^\circ C = 273 + 100 = 373 K$).
• Particles in steam, that is, water vapor at $373 K$ ($100^\circ C$) have more energy than water at the same temperature. This is because particles in steam have absorbed extra energy in the form of latent heat of vaporization.
• The state of matter can be changed into another state by changing the temperature. Substances around us change state from solid to liquid and from liquid to gas on the application of heat. But some change directly from the solid-state to the gaseous state and vice versa without changing into the liquid state.

Note: Kelvin is the SI unit of temperature, $0^\circ C = 273.15 K$. For convenience, we take $0^\circ C = 273 K$ after rounding off the decimal. To change a temperature on the Kelvin scale to the Celsius scale, subtract 273 from the given temperature, and to convert a temperature on the Celsius scale to the Kelvin scale, add 273 to the given temperature.

Activity 1.13: Sublimation of Camphor
* Take some camphor, crush it, and put it in a china dish.
* Put an inverted funnel over the china dish.
* Put a cotton plug on the stem of the funnel.
* Now, heat slowly and observe.

• A change of state directly from solid to gas without changing into the liquid state is called sublimation, and the direct change of gas to solid without changing into the liquid is called deposition.

1.4.2 Effect of Change of Pressure

• The difference in various states of matter is due to the difference in the distances between the constituent particles. Applying pressure and reducing temperature can liquefy gases.
• Applying pressure and reducing temperature can liquefy gases.
• Solid $CO_2$ gets converted directly into a gaseous state on a decrease of pressure to 1 atmosphere without coming into a liquid state. This is the reason that solid carbon dioxide is also known as dry ice.
• Pressure and temperature determine the state of a substance, whether it will be solid, liquid, or gas.

atmosphere (atm) is a unit of measuring pressure exerted by a gas. The unit of pressure is Pascal (Pa): 1 atmosphere = $1.01 × 10^5 Pa$. The pressure of air in the atmosphere is called atmospheric pressure. The atmospheric pressure at sea level is 1 atmosphere and is taken as the normal atmospheric pressure.

1.5 Evaporation

• Evaporation is the phenomenon of change of liquid into vapors at any temperature below its boiling point.

1.5.1 Factors Affecting Evaporation

Activity 1.14: Factors Affecting Evaporation
* Take 5 mL of water in a test tube and keep it near a window or under a fan.
* Take 5 mL of water in an open china dish and keep it near a window or under a fan.
* Take 5 mL of water in an open china dish and keep it inside a cupboard or on a shelf in the class.
* Record the room temperature.
* Record the time or days taken for the evaporation process in the above cases.
* Repeat the above three steps of activity on a rainy day and record observations.

• Observations on the effect of temperature, surface area, and wind velocity (speed) on evaporation:
  • An increase in surface area increases the rate of evaporation.
  • An increase in temperature increases the rate of evaporation because more particles gain enough kinetic energy to go into the vapor state.
  • A decrease in humidity increases the rate of evaporation as humidity is the amount of water vapor present in the air.
  • An increase in wind speed increases the rate of evaporation because the particles of water vapor move away with the wind, decreasing the amount of water vapor in the surrounding.

1.5.2 How Does Evaporation Cause Cooling?

• In an open vessel, the liquid keeps on evaporating. The particles of liquid absorb energy from the surrounding to regain the energy lost during evaporation. This absorption of energy from the surroundings makes the surroundings cold.
• When acetone (nail polish remover) is poured on the palm, the particles gain energy from the palm or surroundings and evaporate, causing the palm to feel cool.
• After a hot sunny day, people sprinkle water on the roof or open ground because the large latent heat of vaporization of water helps to cool the hot surface.
• During summer, we perspire more because the body's mechanism keeps us cool. During evaporation, the particles at the surface of the liquid gain energy from the surroundings or body surface and change into vapor. The heat energy equal to the latent heat of vaporization is absorbed from the body, leaving the body cool.
• Cotton, being a good absorber of water, helps in absorbing sweat and exposing it to the atmosphere for easy evaporation. Water vapor present in the air, on coming in contact with the cold glass of water, loses energy and gets converted to a liquid state, which we see as water droplets.

Key Concepts

• Matter is made up of small particles.
• The matter around us exists in three states—solid, liquid, and gas.
• The forces of attraction between the particles are maximum in solids, intermediate in liquids, and minimum in gases.
• The spaces in between the constituent particles and the kinetic energy of the particles are minimum in the case of solids, intermediate in liquids, and maximum in gases.
• The arrangement of particles is most ordered in the case of solids; in the case of liquids, layers of particles can slip and slide over each other, while for gases, there is no order; particles just move about randomly.
• The states of matter are inter-convertible. The state of matter can be changed by changing temperature or pressure.
• Sublimation is the change of solid-state directly to the gaseous state without going through the liquid state.
• Deposition is the change of the gaseous state directly to the solid-state without going through the liquid state.
• Boiling is a bulk phenomenon. Particles from the bulk (whole) of the liquid change into the vapor state.
• Evaporation is a surface phenomenon. Particles from the surface gain enough energy to overcome the forces of attraction present in the liquid and change into the vapor state.
• The rate of evaporation depends upon the surface area exposed to the atmosphere, the temperature, the humidity, and the wind speed.
• Evaporation causes cooling.
• Latent heat of vaporization is the heat energy required to change 1 kg of a liquid to gas at atmospheric pressure at its boiling point.
• Latent heat of fusion is the amount of heat energy required to change 1 kg of solid into liquid at its melting point.
• Some measurable quantities and their units to remember:
  • Temperature Unit: Kelvin, Symbol: K
  • Length Unit: Metre, Symbol: m
  • Mass Unit: Kilogram, Symbol: kg
  • Weight Unit: Newton, Symbol: N
  • Volume Unit: Cubic Metre, Symbol: $m^3$
  • Density Unit: Kilogram per Cubic Metre, Symbol: kg $m^{-3}$
  • Pressure Unit: Pascal, Symbol: Pa