Chemicals and chemical changes.

Chemical Substances

Types of Chemical Substances

1. Pure Substances: Elements or compounds.

2. Mixtures: Combination of two or more substances not chemically combined.

Elements

1

. Definition: Substance made up of only one kind of atoms.

2.

Properties: Each element has its own distinct set of properties.

3. Examples: Silver, gold, aluminium, hydrogen, oxygen.

Compounds

1. Definition: Substance formed when

two or more elements combine chemically.

2. Properties: Properties of a compound differ from those of its constituent elements.

3. Examples

 Mixtures**

1 . Definition: Combination of two or

more substances not chemically combined.

2

. Properties: Retains properties of its components.

3. Examples: Air, mixture of iron filings and sulphur.

Chemical Symbols

1. Definition: Abbreviations used to represent elements.

2. Purpose: Simplifies writing and communication in chemistry.

Chemical Symbols and Atomicity

History of Chemical Symbols

1. Early Symbols: Pictorial symbols used by John Dalton.

2. Modern System: Developed by Jons Jacob Berzelius using letters of the English alphabet.

Features of Modern Chemical Symbols

1. First Letter: First letter of the element's name is used as its symbol.

2. Additional Letters: Second letter or distinct letter added when necessary.

3. Latin Names: Some symbols derived from Latin names (e.g., Au for Gold, Ag for Silver).

Examples of Chemical Symbols

1. Elements: H (Hydrogen), C (Carbon), O (Oxygen), N (Nitrogen).

2. Symbols from Latin Names: Na (Sodium), K (Potassium), Pb (Lead).

Chemical Formulae and Equations

Chemical Formulae

1. Definition: Representation of a molecule of a compound using chemical symbols of its constituent elements.

2. Examples: H2O (water), NaCl (common salt), CaCO3 (calcium carbonate).

Valency

1. Definition: Combining capacity of an atom of an element.

2. Examples: Hydrogen (1), Oxygen (2), Carbon (4).

Writing Chemical Formulae

1. Steps:

Write symbols of constituent elements.

Write valencies of elements.

Cross over valencies and write as subscripts.

Simplify formula if possible.

Atomicity

1

. Definition: Number of atoms present in one molecule of an element.

2. Types:

Monatomic: 1 atom (e.g., noble gases).

Diatomic: 2 atoms (e.g., oxygen, 02).

Tetratomic: 4 atoms (e.g.,

phosphorus, P4).

Chemical Equations

1 . Definition: Shorthand form of

representing a chemical reaction using symbols and formulae.

2. Components:

Reactants: Substances involved initially in the reaction.

Products: New substances formed in the reaction.

Writing Chemical Equations

1. Steps:

Identify reactants and products.

Write names of reactants on the left-hand side with a '+' sign between them.

Write names of products on the right-hand side with a '+' sign between them.

Use an arrow (→) to separate reactants from products.

Chemical Equations

Writing Chemical Equations

1. Steps:

Identify reactants and products.

Write names of reactants on the left-hand side with a '+' sign between them.

Write names of products on the right-hand side with a '+' sign between them.

Use an arrow (→) to separate reactants from products.

2. Example: Magnesium burns in oxygen to form magnesium oxide.

Word equation: magnesium + oxygen → magnesium oxide

Chemical equation: 2Mg + 02 → 2MgO

Balancing Chemical Equations

1. Definition: Ensuring the number of atoms of each element is equal on both sides of the equation.

2. Steps:

Count the number of atoms of each element on both sides.

Adjust coefficients to balance the equation.

Examples of Chemical Changes

1. Rusting of Iron: Iron reacts with

oxygen and moisture to form iron oxide (rust).

Chemical equation: 4Fe + 302 + 6H2O → 4Fe(OH)3

Importance of Chemical Equations

1. Representation: Chemical equations

represent chemical reactions in a concise and symbolic way.

2. Balancing: Balancing chemical equations ensures the law of conservation of mass is obeyed

Balancing Chemical Equations

1. Definition: Ensuring the number of atoms of each element is equal on both sides of the equation.

2. Steps:

Count the number of atoms of each element on both sides.

Adjust coefficients to balance the equation.

Examples of Chemical Changes

1. Rusting of Iron: Iron reacts with

oxygen and moisture to form iron oxide (rust).

Chemical equation: 4Fe + 302 + 6H2O → 4Fe(OH)3

Importance of Chemical Equations

1. Representation: Chemical equations

represent chemical reactions in a concise and symbolic way.

2. Balancing: Balancing chemical equations ensures the law of conservation of mass is obeyed.

Chemical Changes

Examples of Chemical Changes

1. Rusting of Iron: Iron reacts with

oxygen and moisture to form iron oxide (rust).

Conditions: Oxygen and water are essential for rusting.

Prevention: Oiling or galvanizing iron objects can prevent rusting.

2. Browning of Vegetables and Fruits:

Cut surfaces of vegetables and fruits turn brown due to reaction with atmospheric oxygen.

Prevention: Soaking cut vegetables and fruits in plain water can reduce browning.

3. Reaction between Vinegar and Baking Soda: Produces carbon dioxide gas.

Chemical equation: CH3COOH + NaHCO3 CH3COONa CO2 + H2O +

4. Reaction between Copper Sulphate Solution and Iron Nails: Iron displaces

copper from copper sulphate solution,

forming iron sulphate and copper.

Chemical equation: CuSO4 + Fe → FeSO4 + Cu

Characteristics of Chemical Changes

1. Permanent Change: Chemical

changes are often irreversible.

2. New Substances Formed: Chemical changes result in the formation of new substances with different properties

Physical and Chemical Changes

Physical Changes

1. Definition: Changes in which no new substances are formed.

2. Examples: Formation of ice from water, crystallization of common salt.

3. Characteristics: Properties such as color, shape, size, or physical form may change.

Chemical Changes

1. Definition: Changes in which new substances are formed.

2. Examples: Rusting of iron, reaction

between vinegar and baking soda, reaction between copper sulphate solution and iron nails.

3. Characteristics: Permanent change, new substances formed with different properties.

Crystallization

1. Definition: Process of obtaining crystals of a substance from its solution.

2. Example: Crystallization of common salt from seawater.

3. Steps:

Dissolve impure substance in water.

Filter the solution to remove insoluble impurities.

Allow the solution to cool and form crystals.

Examples of Chemical Reactions

1. Rusting of Iron: Iron reacts with

oxygen and moisture to form iron oxide (rust).

2. Reaction between Vinegar and Baking

Soda: Produces carbon dioxide gas.

3. Reaction between Copper Sulphate Solution and Iron Nails: Iron displaces copper from copper sulphate solution, forming iron sulphate and copper.

Understanding secularism

 Secularism: Separation of religion from

the state, ensuring equal treatment of all citizens regardless of their religious beliefs.

Indian Secularism: India adopted a

strategy of separating power from religion and state, preventing any one religion from dominating others.

Objectives:

Prevent one religious community from dominating another.

Ensure the state doesn't enforce any particular religion or take away individual freedom.

Prevent some members from dominating others within the same religious community.

Important Concepts

Secular State: A state that maintains

a principled distance from religion, neither promoting nor interfering with religious practices.

Non-Interference: The state doesn't interfere with religious practices unless they violate fundamental rights or laws.

Intervention: The state may intervene to prevent domination or protect individu rights.

Questions and Answers

1. What is secularism in the Indian context?

Indian secularism refers to the separation of power from religion and state, ensuring equal treatment of all citizens.

2. Why is it important for one religious community not to dominate another?

This ensures equality and prevents tyranny, promoting brotherhood and mutual cooperation.

3. What is the role of the state in promoting secularism? 

The state maintains a principled distance from religion, ensuring equal treatment and preventing domination.

4. Can the government intervene if a religious group says their religion allows infanticide?

Yes, the government can intervene as infanticide is a violation of fundamental rights and laws.

5. What are some examples of secular practices in India?

1.Examples include government schools not promoting any particular religion and laws

2.banning untouchability 

Question 1: Different types of religious practices

People in our neighborhood practice different religions like Hinduism, Islam, Sikhism, and Christianity. They visit temples, mosques, gurudwaras, and churches to pray and worship.

Question 2: Government intervention in infanticide

Yes, the government will stop infanticide because it's a crime and against human rights.

Question 3: Objectives of a secular state

No one religion should dominate another.

The state shouldn't force any particular religion.

Everyone should be equal within their own community.

Question 4: Religious holidays in school calendars

Our school calendar has holidays for different religions like Eid, Diwali, Christmas, and Guru Nanak Jayanti.

Question 5: Different views within the same religion

Yes, there can be different views within the same religion. For example, Hindus worship different gods, and Muslims are divided into Shia and Sunni.

Question 6: Indian state's role in religion

The Indian state respects all religions and doesn't interfere unless someone's rights are violated.

Question 7: Poster on peace and religious tolerance

The poster means that peace requires respecting differences and working together. It promotes harmony and acceptance among people of different religions.

The tsunami

 The Tsunami" chapter tells about the terrible 2004 tsunami.

Part 1: Stories of Bravery and Loss:

 It shares stories from the Andaman and Nicobar Islands.

Ignesious lost his family. Policeman Sanjeev saved others but drowned trying to help. Meghna, a 13-year-old, floated on a door for two days and survived. Almas Javed, 10, also survived byclinging to a log after her family was swept away.

Part 2: Tilly Smith's Quick Thinking

In Thailand, British schoolgirl Tilly Smith noticed the sea acting strangely.

Remembering a geography lesson about tsunamis, she warned her family and others to run to safety, saving many lives.

Part 3: Animals' Sixth Sense

The chapter notes that few animals died in the tsunami. It suggests animals have a "sixth sense" to feel danger. Elephants ran to high ground, and dogs refused to go to the beach, showing their ability to sense the disaster before humans.

In conclusion it shows the tsunami's destruction, human courage, and animals' amazing ability to sense danger.

The best Christmas present in the world summary

 The Best Christmas Present in the World" by Michael Morpurgo is a heartwarming story about the power of hope, peace, and human connection, even in the midst of war.

During World War I, British soldier Jim Macpherson writes a letter to his wife Connie on Christmas Eve, describing a remarkable event. On Christmas Day, Jim's battalion faces off against German soldiers, but instead of fighting, they call out "Merry Christmas" and come together to celebrate. They play an impromptu game of football, share food and drinks, and sing carols together.

In this moment of peace, Jim befriends a German soldier named Hans Wolf, and they discuss their lives, families, and shared love of literature. The letter is a testament to the humanity and kindness that can exist even in the midst of war.

Years later, a narrator discovers Jim's letter and decides to deliver it to Connie, now 101 years old and living in a nursing home. When he hands her the letter, Connie's eyes light up, and she mistakes the narrator for her husband Jim. She's overjoyed, and the letter brings back happy memories of their time together.

Chapter 1:Crop production and management.

 Introduction

Crops are plants that are grown and harvested for food, fiber, or other products.

Crop production involves preparing the soil, sowing seeds, providing nutrients, controlling pests and diseases, and harvesting.

Soil Preparation

1. Ploughing: Breaking up the soil to loosen it and remove weeds.

2.Levelling: Smoothing out the soil surface to ensure even water distribution.

3. Manuring: Adding organic matter to improve soil fertility.

Sowing Seeds

1. Seed selection: Choosing good quality

seeds that are suitable for the climate and soil.

2. Sowing depth: Sowing seeds at the correct depth to ensure proper germination.

3. Seed spacing: Planting seeds at the

correct distance to ensure proper growth.

Crop Management

1. Irrigation: Providing water to crops

through various methods like sprinklers, drip irrigation, or flood irrigation.

2. Fertilizers: Adding nutrients to the soil to promote healthy plant growth.

3. Pest control: Protecting crops from

pests and diseases using various methods like pesticides, biological control, or cultural control.

Harvesting and Storage

1. Harvesting: Cutting and gathering crops when they are mature.

2. Storage: Storing harvested crops in a dry, cool place to maintain their quality.

Types of Crops

1. Kharif crops: Crops grown during the monsoon season, such as rice, maize, and cotton.

2. Rabi crops: Crops grown during the

winter season, such as wheat, barley, and mustard.

Conclusion

Crop production and management involve various steps to ensure a healthy and productive crop. Understanding these steps is essential for farmers and agricultural professionals.

Chemical effect of electric current.

 

Introduction

Electric current can cause chemical changes in certain substances.

These chemical changes can be used for various applications.

Electrolysis

1. Definition: Electrolysis is the process

of using electric current to cause a chemical change in a substance.

2. Examples: Electrolysis of water, electroplating, and extraction of metals.

Electroplating

1. Definition: Electroplating is the process of depositing a thin layer of a material on an object using electrolysis.

2. Applications: Electroplating is used to protect metals from corrosion, improve appearance, and enhance durability. 

Chemical Effects of Electric Current

1. Decomposition: Electric current can cause decomposition of certain substances.

2. Chemical reactions: Electric current can initiate chemical reactions, leading to the formation of new substances.

Applications

1. Electroplating: Used for decorative and protective purposes.

2. Purification of metals: Used to purify metals like copper and zinc.

3. Extraction of metals: Used to extract metals like aluminum and sodium.

Conclusion

Electric current can cause significant chemical changes in substances, and understanding these effects is crucial for various applications. 

Understanding the constitution :class 8 chapter 1 political science

 1. Why does a democratic country need a Constitution?

A democratic country needs a Constitution to establish rules and limits for the government, protect citizens' rights, and ensure fairness and justice.

2. What is the difference in who exercises Executive Power in the above two Constitutions of Nepal?

In the 1990 Constitution, executive power was vested in the King and the Council of Ministers. In the 2015 Constitution, executive power is vested only in the Council of Ministers, indicating a shift towards a more democratic system.

3. What would happen if there were no restrictions on the power of elected representatives?

If there were no restrictions, elected representatives might misuse their power, become tyrannical, and disregard citizen4. Identify the minority and importance of respecting their views:

4. Identify the minority and importance of respecting their views:

(a) Minority: Female teachers. Respecting their views promotes gender equality.

(b) Minority: Buddhists. Respecting their views ensures religious tolerance.

(c) Minority: Non-vegetarians. Respecting their views accommodates dietary diversity.

(d) Minority: Students from less well-off families. Respecting their views promotes social equality.

5. Significance of key features:

Federalism: Allows power sharing

between central and state governments, promoting regional autonomy.

Separation of Powers: Prevents

concentration of power, ensuring checks and balances.

Fundamental Rights: Protects citizens' basic rights and freedoms.

Parliamentary Form of Government:

Ensures accountability of the government to elected representatives.

6. Indian States sharing borders with neighbouring nations:

(a) Bangladesh: West Bengal, Assam, Meghalaya, Tripura, Mizoram

(b) Bhutan: West Bengal, Assam, Arunachal Pradesh, Sikkim

(c) Nepal: Uttarakhand, Uttar Pradesh, Bihar, West Bengal, Sikkim