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Questions and Answers
Which of the following scenarios best illustrates a physical change?
Which of the following scenarios best illustrates a physical change?
- Melting of ice into water without altering its chemical composition. (correct)
- Digestion of food breaking down complex molecules.
- Burning wood, which produces ash, carbon dioxide, and other gases.
- Iron rusting when exposed to moisture and air.
A student observes a white substance dissolving in water, and the solution becomes cold. Which conclusion can be accurately drawn?
A student observes a white substance dissolving in water, and the solution becomes cold. Which conclusion can be accurately drawn?
- A physical change has occurred, and the process is endothermic. (correct)
- A chemical change has occurred, and the process is exothermic.
- A physical change has occurred because the substance's state changed.
- A chemical change has occurred because the temperature changed.
Which of the following is a necessary condition for iron to rust?
Which of the following is a necessary condition for iron to rust?
- Exposure to carbon dioxide and low humidity.
- Contact with both oxygen and water. (correct)
- Immersion in an acidic solution only.
- Presence of nitrogen and high temperatures.
What is the purpose of galvanization in preventing rust?
What is the purpose of galvanization in preventing rust?
Consider a scenario where magnesium ribbon is burned in the presence of oxygen. Which of the following observations would indicate that a chemical change has occurred?
Consider a scenario where magnesium ribbon is burned in the presence of oxygen. Which of the following observations would indicate that a chemical change has occurred?
Why is digestion considered a chemical change?
Why is digestion considered a chemical change?
Which of the following indicates that a chemical change has definitely occurred?
Which of the following indicates that a chemical change has definitely occurred?
What type of change is crystallisation?
What type of change is crystallisation?
Why does cutting a log of wood into pieces represent a physical change, while burning it is a chemical change?
Why does cutting a log of wood into pieces represent a physical change, while burning it is a chemical change?
In the copper sulphate and iron nail activity, what evidence suggests a chemical reaction occurred?
In the copper sulphate and iron nail activity, what evidence suggests a chemical reaction occurred?
What role does ozone play in protecting the Earth, and what type of change occurs when it provides this protection?
What role does ozone play in protecting the Earth, and what type of change occurs when it provides this protection?
How does increasing humidity affect the rate of iron rusting and why?
How does increasing humidity affect the rate of iron rusting and why?
In the experiment involving vinegar and baking soda, what evidence indicates a new substance has been formed?
In the experiment involving vinegar and baking soda, what evidence indicates a new substance has been formed?
Why is stainless steel resistant to rusting, unlike regular iron?
Why is stainless steel resistant to rusting, unlike regular iron?
When carbon dioxide is passed through lime water, it turns milky. What compound is formed that causes this?
When carbon dioxide is passed through lime water, it turns milky. What compound is formed that causes this?
Flashcards
Physical Change
Physical Change
Changes affecting shape, size, color, or state; generally reversible and form no new substances.
Physical Properties
Physical Properties
Properties like shape, size, color, and state of a substance.
Chemical Change
Chemical Change
Change where one or more new substances are formed; also called a chemical reaction.
Rusting
Rusting
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Galvanization
Galvanization
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Crystallization
Crystallization
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Study Notes
- Many changes occur daily in our surroundings, involving one or more substances.
- Changes are broadly classified into physical and chemical changes.
Physical Changes
- Physical changes affect physical properties like shape, size, color, and state.
- Generally reversible, and no new substances are formed during a physical change.
- Examples include:
- Cutting paper
- Chalk changing size
- Water changing state (solid to liquid to gas)
Chemical Changes
- Chemical changes, also called chemical reactions, involve the formation of new substances.
- Accompanied by:
- Release or absorption of heat, light, or radiation
- Production of sound
- Change in smell
- Color change
- Formation of gas
- Examples:
- Rusting of iron
- Burning magnesium ribbon
- Reaction of copper sulfate with iron
Rusting of Iron
- Rusting is a chemical change where iron reacts with oxygen and water to form rust (iron oxide).
- Essential for rusting: presence of oxygen and water.
- Rusting is faster in humid conditions.
- Prevention:
- Applying paint or grease
- Coating with chromium or zinc (galvanization)
- Stainless steel (iron mixed with carbon, chromium, nickel, and manganese) does not rust.
Other Chemical Reactions
- Magnesium reacts with oxygen to form magnesium oxide (ash).
- Mg + O₂ → MgO
- Magnesium oxide dissolves in water to form magnesium hydroxide (a base).
- MgO + H₂O → Mg(OH)₂
- Copper sulphate reacts with iron to form iron sulphate and copper.
- Vinegar (acetic acid) and baking soda react to produce carbon dioxide, which turns lime water milky.
Crystallisation
- Process of obtaining large, pure crystals of a substance from its solution.
- Example: Obtaining copper sulphate crystals by dissolving copper sulphate powder in water, heating, filtering, cooling, and allowing crystals to form.
Additional Points
- Ozone layer protects from harmful ultraviolet radiation by breaking down into oxygen, a chemical change.
- Galvanisation is a process of depositing a layer of zinc on iron to prevent rusting
- Photosynthesis and digestion are examples of chemical changes
- The iron pillar near Qutub Minar in Delhi, made over 1600 years ago, has not rusted, demonstrating advanced metal technology in ancient India.
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