5. Substances in the Surroundings-Their States and Properties
States of Water:
Solid: Ice
Liquid: Water
Gas: Water vapour (steam)
Change of State of Substances:
When a substance transitions from one state (solid, liquid, gas) to another, this is known as a "change of state."
Activity with Wax:
1. Heating Wax:
Upon heating, the solid wax melts and turns into a liquid.
2. Initial State of Wax:
Solid
3. After Heating:
Wax becomes a liquid.
When cooled in cold water, the wax solidifies again, returning to its original solid state.
This illustrates melting (solid to liquid) and solidification (liquid to solid) as examples of change of state.
Important Questions:
1. Substances Freezing in Winter:
Ghee, coconut oil
2. Liquids Changing into Vapour:
Spirit, petrol, camphor
3. Solids Subliming (Directly Changing to Gas):
Camphor, naphthalene balls, ammonium chloride
Key Learning Points:
The state of a substance (solid, liquid, or gas) depends on temperature.
Substances can transition between states when heated (melting, evaporation) or cooled (solidification, condensation).
Some substances can skip the liquid state, directly changing from solid to gas (sublimation).
Scientist Contribution:
J. Willard Gibbs (19th Century):
Demonstrated that the physical state of a substance influences its properties and depends on the arrangement of its particles.
These concepts are essential for understanding the behavior of materials in our environment.
Detailed Characteristics of Solids, Liquids, and Gases:
1. Solids:
Example: A piece of iron.
Shape: Solids have a definite shape of their own and retain this shape regardless of how they are placed or kept.
Volume: Solids have a fixed, definite volume. When solids like sugar or sand are poured onto a flat surface, they form a heap instead of spreading out evenly.
2. Liquids:
Examples: Water, spirit, oil.
Shape: Liquids do not have a shape of their own. They take the shape of the container they are placed in, meaning they adapt their form to the boundaries of the container.
Volume: Liquids have a specific volume, meaning they occupy a definite portion of the container. Liquids can spread out on a flat surface when poured and flow down slopes due to gravity.
3. Gases:
Example: Air.
Shape: Gases do not have a shape of their own and spread to fill all available space within a container.
Volume: Gases do not have a definite volume. When gases are placed in a closed container, the volume they occupy can change depending on the pressure applied.
Heat and Change of Physical State:
Heat causes substances to change between their solid, liquid, and gaseous states.
On Heating:
Solids change into liquids (melting).
Liquids change into gases (evaporation/vaporization).
On Cooling:
Gases change into liquids (condensation).
Liquids change into solids (freezing).
This process is also known as a phase change, where energy (heat) is either absorbed or released to cause the change in state.
Questions for Thought:
Does water change into vapor immediately when heated on a stove?
Ans-
No, water does not immediately change into vapor when heated on a stove. It first absorbs heat and its temperature rises gradually. Once it reaches its boiling point (100°C or 212°F at sea level), it starts to convert into vapor. The process continues as long as heat is supplied.
Does water freeze into ice as soon as it is placed in a fridge?
Ans-
No, water does not freeze into ice as soon as it is placed in a fridge. The temperature of the water needs to drop below 0°C (32°F) for it to freeze, and this process takes time depending on the temperature inside the fridge or freezer, the amount of water, and the container it's in.
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The change in physical state requires the substance to gain or lose a specific amount of heat before transitioning to another state.
Measuring Temperature:
Thermometer: A device used to measure the temperature of a substance.
When a substance gains heat, it warms up, and eventually becomes hot. If the temperature becomes too high, it can cause burns or scalds when touched.
Using your hand to measure temperature is inaccurate and potentially dangerous.
Types of Thermometers:
1. Mercury Thermometer: The traditional thermometer, where mercury inside expands or contracts depending on the temperature, giving an accurate reading.
2. Digital Thermometer: Modern thermometers that show a digital readout of temperature, often in degrees Celsius (°C).
Measuring Temperature and Boiling
1. Measuring Temperature using a Thermometer:
1) The thermometer bulb contains mercury.
2) The level of mercury in the capillary tube rises or falls based on temperature.
3) The temperature is read from the scale beside the mercury column.
4) To measure the temperature of water:
5) Immerse the bulb in water fully.
6) Record the temperature of hot and cold water.
Examples of Temperatures:
Boiling water: 100°C
Freezing water: 0°C
Air (winter night): <15°C
Air (summer afternoon): >35°C
Inside a fridge: <5°C
Inside the freezer: -18°C
Body temperature: ~37°C
2. Boiling:
1. Water evaporates continuously at all temperatures, but evaporation is faster at higher temperatures.
2. As water is heated, the temperature increases and evaporation rate rises.
Boiling of Water (Ebullition):
1. At sea level, water boils at 100°C.
2. Bubbles rise as the water reaches the boiling point.
Condensation:
1. Water vapor condenses back to liquid when cooled.
2. Boiling point (100°C) and condensation point are the same.
Notes on Changes in Physical State (Page 35):
Key Concepts:
1. Boiling and Melting:
When a substance gains heat, it either melts or boils depending on its state (solid to liquid, or liquid to gas).
2. Condensation and Freezing:
When a substance loses heat, it condenses (gas to liquid) or freezes (liquid to solid).
3. Freezing Point:
The temperature at which water or other substances turn into ice (solid form).
For water, this point is 0°C, which is the same as its melting point.
4. Temperature Below Freezing:
Temperatures below freezing (e.g., -18°C in freezers) show how water freezes below 0°C.
5. Melting Point:
The same temperature as the freezing point of a substance (e.g., ice melts at 0°C).
6. Boiling Point:
Each substance has its specific boiling point (where it turns from liquid to gas).
7. Condensation Point:
The same as the boiling point but occurs during cooling.
Examples of Substances and Their States:
Candle: Freezing point 60°C, Boiling point 350°C.
Plastic: Freezing point above 250°C, Boiling point 954°C.
Iron: Freezing point 1535°C, Boiling point 2862°C.
Practical Uses:
1. Candles: Made by melting paraffin wax.
2. Dry Ice (solid CO₂): Used for cooling, like in ice cream and freezing.
3. Liquid Nitrogen: Used in animal husbandry.
4. Silica (sand): Melted to make glass.
5. Metals (Gold and Silver): Melted to make jewelry.
6. Iron: Melted to create tools.
Key Observations:
The boiling point and freezing point provide insight into whether a substance is solid, liquid, or gas at room temperature.
Sublimation Experiment:
Setup:
1. A crucible is filled with sand and a few iodine crystals.
2. The crucible is placed on a tripod for heating.
3. A funnel is inverted over the crucible, with its stem blocked using a cotton plug.
4. A burner is lit beneath the crucible to heat the iodine.
Observation:
Iodine crystals do not melt but sublimate (change from solid to gas).
The gaseous iodine particles cool and solidify, sticking to the funnel walls.
Conclusion:
The process is sublimation, where a solid transitions directly into a gas without becoming a liquid first.
Use Your Brain Power:
Why does the smell of camphor spread when a box is opened?
Camphor also sublimates, changing directly from solid to gas, which allows its smell to spread quickly.
Identifying Substances:
How to identify the following:
Glass: Determine if it is plastic, steel, or glass based on properties like transparency.
Rod: Identify whether it is iron or aluminum by its weight, color, and magnetic properties.
Door: Check if it is wooden or glass by looking at the material and texture.
White powder: Test if it is salt or chalk by checking properties like solubility in water.
Key properties for identification:
Transparency
Hardness
Weight
Color
Sound produced
Solubility in water
Properties of Substances
1. Brittleness :
When pressure is applied to substances like chalk, brick, alum, glass, or rajgira wadi, they break into small pieces or particles.
Such substances are called brittle.
Definition: Brittleness is the property of substances that allows them to break into pieces under pressure.
2. Hardness :
Example: An iron nail easily pierces wet mud but faces resistance with cardboard and wood.
Definition: Hardness is determined by the amount of resistance a substance offers when another object is pushed through it.
Note: The hardest known substance is diamond.
3. Elasticity :
Examples: Stretching a rubber band or applying pressure on a sponge.
These substances return to their original shape after the applied force is removed.
Definition: Elasticity is the property of substances that enables them to regain their original shape after deformation.
4. Fluidity :
Experiment: Dropping water, honey, and gum on a sloping metal sheet shows how liquids flow.
Definition: Fluidity is the ability of a liquid to flow. Liquids flow downwards on a sloping surface, and fluidity is determined by how easily the liquid flows.
5. Density:
When two blocks of the same size (e.g., wood and iron) are compared, the iron block is heavier due to its higher density.
Definition: Density is the property that describes the mass per unit volume of a substance. Substances with greater density are heavier than those with lower density, even if they have the same volume.
6. Solubility:
Certain solid substances dissolve in specific liquids. This ability to dissolve is called solubility.
Examples:
Salt is soluble in water but insoluble in kerosene.
Sugar is soluble in water but may not dissolve in kerosene.
Fine sand does not dissolve in water or kerosene, hence is insoluble.
7.Transparency:
A substance is transparent when we can see through it, meaning light passes through it.
Examples of transparent materials: glass, some plastics, clean water, air.
Metals:
Metals include substances like copper, gold, iron, and aluminium.
These substances are obtained from minerals found in the earth's crust.
Metals are a group of substances with various uses in daily life.
Properties of Metals:
Malleability:
The property by which metals can be hammered into thin sheets.
Example: Hammering a piece of copper or aluminium wire flattens it.
Ductility
Metals can be hammered and stretched into thin sheets or drawn into wires.
Ductility: The property of metals that allows them to be drawn into wires.
Common examples: Silver, gold, copper, platinum.
Electrical Conductivity
Electrical Conductivity: Metals allow electricity to pass through them.
All metals are conductors of electricity to varying degrees.
Thermal Conductivity
Thermal Conductivity: Metals transfer heat when heated at any one point, making the whole object hot.
Example: A metal rod being heated at one end.
Lustre
Metals have a natural shine called lustre, and their unique color helps in identification.
Example: Gold's characteristic yellow color, silver's reflective shine.
Sonority
Metals produce a ringing sound when struck. This property is known as sonority.
Example: The sound produced when a bell is struck or a string of an instrument is plucked.
Practical Observations:
1. Why are electric boards fitted on the wall made of plastic or wood?
Plastic and wood are insulators; they do not conduct electricity, making them safe for use in electrical installations.
2. Why is the handle of a cooker made of plastic?
Plastic is a poor conductor of heat, preventing the handle from becoming too hot and making it safe to touch.
Experimental Observations:
Striking metals produces a ringing sound (sonority), whereas striking wood or marble does not produce this effect.
Uses of Metals
Metals are used in various industries due to their ductility, cond
uctivity (thermal and electrical), lustre, and sonority.
Safety Precautions:
Avoid touching exposed electric wires or metal parts, especially during the rainy season.
Switch off electric appliances, including the main switch of the TV, to save electricity and prevent accidents.
Ensure regular checks of electric wiring and fittings by seniors or professionals.
Key Scientific Concepts:
1. States of Substances:
Solids, liquids, and gases.
2. Measuring Temperature:
Thermometers are used to measure how hot or cold a substance is.
3. Heat and Change of State:
Heat is responsible for changing the state of substances (solid to liquid, liquid to gas, etc.).
4. Properties of Substances:
Include hardness, elasticity, brittleness, fluidity, density, solubility, and transparency.
5. Metals and Their Properties:
Metals are a distinct group with properties like malleability, ductility, thermal and electrical conductivity, sonority, lustre, and specific colours.
Science Awareness:
Science is continuously evolving. Stay updated with research at state, national, and global levels.
Read newspapers regularly to stay informed about scientific developments.
Collect and share scientifica rticles to enhance knowledge and discussion.
