CLASS 9TH DAY 1

INTRODUCTION

STATES OF MATTER

The following video is an introduction to matter and states of matter. Please go through it.

Terms & Definitions👇 👇

Anything that occupies space and has mass is called matter. For example: Chair, bed, river, mountain, dog, tree, building, etc.

Characteristics of matter:

Matter is made up of small particles called atoms.
These particles are too small to be observed with naked eye.
These particles are constantly moving constantly.
These particles have spaces between them.
Particles of matter attract each other because of the force of attraction.

Change of State of Matter:

Physical states of matter can be inter converted into each other by following two ways:

By changing the temperature
By changing the pressure

Effect of Change of Temperature:

(a)Solid to liquid:

On increasing the temperature of solids, the kinetic energy of the particles increases which overcomes the forces of attraction between the particles thereby solid gets converted to a liquid.
Melting: Change of solid state of a substance into liquid is called melting.
Melting point: The temperature at which a solid melts to become a liquid at the atmospheric pressure is called its melting point.
Melting point of ice is 0oc.

(b) Liquid to gas:

On heating a liquid like water, the kinetic energy of its particles increases as high as in a gas, thus causing the liquid to change to a gas.
Boiling: The change of a liquid substance into gas on heating is called boiling.
Boiling point: The temperature at which a liquid boils and changes rapidly into a gas at the atmospheric pressure is called its boiling point.
Boiling point if water is 100oC.
On cooling a gas like steam (or water vapour), the kinetic energy of its particles is lowered down, causing them to move slowly and bringing them closer, forming a liquid.
Condensation: The process, in which a gas, on cooling, turns into a liquid at a specific temperature is called condensation or liquefaction.

(c) Liquid to solid:

When a liquid is cooled down by lowering its temperature, its particles lose the kinetic energy and come to a stationary position, causing the liquid to turn to solid.
Freezing: The change of a liquid substance into solid by lowering its temperature is called freezing.
Freezing point: The temperature at which the state of a substance changes from a liquid to a solid is called the freezing point of that substance.

Fusion:The process of melting, that is, change of solid state into liquid state is also known as fusion.

Latent heat: The heat energy that is required to change the state of a substance without causing any ruse in the temperature of the substance is called latent heat. Since, the heat energy is hidden in the bulk of the matter, it is called latent heat.

Latent heat of fusion: The heat energy required to convert 1 kilogram of a solid into liquid at atmospheric pressure, at its melting point, is known as the latent heat of fusion
Latent heat of vaporization: The heat energy required to convert 1 kilogram of liquid into gas, at atmospheric pressure, at its boiling point, is known as the latent heat of vaporization
Note: Water vapour at 373 K have more energy than water at the same temperature because
particles in steam have absorbed extra energy in the form of latent heat of vaporization.

Sublimation: The change of state of a substance directly from a solid to gas or gas to solid, without changing into the liquid state, is called sublimation.

Effect of change of pressure:

Gas to liquid: Gases can be liquefied by applying pressure and reducing the temperature. When a high pressure is applied to a gas, it gets compressed and if the temperature is lowered, the gas is liquefied.
Solid CO2 gets converted directly to gaseous state on decrease of pressure to 1 atmosphere without coming into liquid state. This is the reason that solid carbon dioxide is also known as dry ice.

Activity Discussion

Let’s discuss the activity we did at the end of states of matter video. You must have seen that the water level was less in both the containers. However the water level had gone down more in the container which was kept in sunlight as compared to the container kept inside the house.

Where had the water gone ? Well the water had evaporated. The level had decreased more in container kept outside because rate of evaporation increases due to temperature. Let’s see more about evaporation in the following video.

EVAPORATION

Terms & Definitions

Evaporation:

The process of conversion of a substance from the liquid state to the gaseous state at any temperature below its boiling point is called evaporation or vaporisation.

Factors affecting the rate of evaporation:

Surface area: The rate of evaporation increases on increasing the surface area of the liquid.
Temperature: The rate of evaporation increases with an increase in temperature.
Humidity: Decrease in the humidity increases the rate of evaporation.
Wind speed: An increase in the wind speed increases the rate of evaporation.

Evaporation causes cooling:

During the process of evaporation, the particles of liquid absorb energy or latent heat of vaporization from the surrounding to get converted to gaseous state. This absorption of energy from the surroundings make the surroundings cold.

Water Cycle Example Video👉 👉

Tyndall effect

There are three types of mixtures:

Solutions: A solution is a homogeneous mixture of two or more components. The components of a solution are atoms, ions, or molecules, making them 10-9 m or smaller in diameter.

Example: Sugar and water

Suspensions: The particles in suspensions are larger than those found in solutions. Components of a suspension can be evenly distributed by mechanical means, like by shaking the contents but the components will eventually settle out.

Example: Oil and water

Colloids: Particles intermediate in size between those found in solutions and suspensions can be mixed in such a way that they remain evenly distributed without settling out. These particles range in size from 10-8 to 10-6 m in size and are termed colloidal particles or colloids. The mixture they form is called a colloidal dispersion. A colloidal dispersion consists of colloids in a dispersing medium.

Example: Milk

The Tyndall effect is the phenomenon in which the particles in a colloid scatter the beams of light that are directed at them. This effect is exhibited by all colloidal solutions and some very fine suspensions. Therefore, it can be used to verify if a given solution is a colloid. The intensity of scattered light depends on the density of the colloidal particles as well as the frequency of the incident light.

When a beam of light passes through a colloid, the colloidal particles present in the solution do not allow the beam to completely pass through. The light collides with the colloidal particles and is scattered (it deviates from its normal trajectory, which is a straight line). This scattering makes the path of the light beam visible.

Click on the link to learn more about Tyndall effect.👉 👉

Try this activity at home to understand the tyndall effect better and see it with your own eyes.👇 👇

Step 1: Colloids

You’ll need an eyedropper with a small amount of milk, a spoon, and a beaker with 250 ml of water. Squeeze a few drops of milk from the eyedropper into the beaker and stir. Shine the laser through the beaker and you should now be able to observe the Tyndall effect.

You’ll notice that you can’t see the laser beam piercing through the air, but you can see the beam in the diluted milk and water mixture. A glass of milk is an example of a colloid and the Tyndall effect is what gives it its translucent appearance.

Step 2: Suspensions

Stir 5 grams (1 teaspoon) of dirt from your garden into a beaker with 250 ml (about 8 ounces) of water. Before the dirt settles, shine the laser pointer through the beaker. You should be able to observe the Tyndall effect before the particulate (the particles of dirt suspended in the water) settles to the bottom of the beaker. Suspensions are heterogeneous (lumpy/grainy—the grains of dirt suspended in the water). Particles in a suspension are usually large enough to see with the naked eye or be viewed through an optical microscope. They are often large enough to be filtered from the water, and, of course, will eventually settle to the bottom of the beaker.

Step 3: Solutions

Stir 5 grams (1 teaspoon) of table salt (NaCl) into a beaker with 250 ml (about 8 ounces) of water. Stir until all the salt (solute) dissolves in the water (solvent). When the NaCl dissolves in water it separates into sodium (Na+) cations and chloride (Cl-) anions too small to be seen with the naked eye and will not scatter the light from the laser beam.

Shine the laser pointer through the beaker containing the saline solution and, well, nothing interesting was supposed to happen. But you can see the Tyndall Effect in my sample of table salt and water.

Step 4: Conclusion

To conlclude, you can demonstrate the Tyndall effect with a laser pointer to see Tyndall scattering in a colloid (milk), and in a suspension (dirt).

Milk is mostly an emulsion of milk fat and water. The milk fat globules are too small to be seen with the naked eye or even through an optical microscope, but (unlike a solution) are large enough to scatter light and create the Tyndall effect.

FUN ACTIVITY: How to tie a tie?

Most of us wear a tie to school. It is a daily struggle for some of us, and some just get the knot tied once and hope it doesn’t open. Sometimes we also want to experiment with the tie knot for events or formal gatherings. So click on the link below to learn 8 ways to tie a tie knot.