Chemical and Physical Changes
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Questions and Answers

What happens to water when it changes from solid to liquid?

  • It forms a new substance.
  • It undergoes a chemical change.
  • It undergoes a physical change. (correct)
  • It loses its physical properties.

    • What can be observed when steam from boiling water contacts an inverted pan?

  • Water droplets form on the inner surface. (correct)
  • No physical change occurs.
  • The gas will turn into a solid.
  • The pan will get hotter.

    • Which of the following is a characteristic of a physical change?

  • Includes chemical reactions.
  • Properties such as shape can change. (correct)
  • The change is generally irreversible.
  • New substances are formed.

    • What causes a hack-saw blade to change color when heated?

    <p>It reacts chemically with the flame.</p> Signup and view all the answers

    What is rust?

    <p>An iron oxide that forms in moisture.</p> Signup and view all the answers

    What type of change occurs during the explosion of a firework?

    <p>Chemical change</p> Signup and view all the answers

    Which of the following processes is an example of a chemical change?

    <p>Photosynthesis in plants</p> Signup and view all the answers

    What is a common result of leaving iron objects exposed to air?

    <p>They rust over time.</p> Signup and view all the answers

    Which substance is formed as a result of rusting?

    <p>Iron oxide</p> Signup and view all the answers

    What type of change does the rusting of iron represent?

    <p>An irreversible chemical change.</p> Signup and view all the answers

    Which of the following correctly describes physical properties?

    <p>They are characteristics such as shape, size, and color.</p> Signup and view all the answers

    What condition is necessary for rusting to occur?

    <p>Oxygen and water</p> Signup and view all the answers

    What evidence indicates that spoilage of food is a chemical change?

    <p>Production of foul smell</p> Signup and view all the answers

    How can we characterize the browning of a cut apple over time?

    <p>Chemical change</p> Signup and view all the answers

    Which of the following is NOT a characteristic of chemical changes?

    <p>Reversibility under normal conditions</p> Signup and view all the answers

    What is the primary reason we must be cautious with fireworks?

    <p>They produce harmful pollutants</p> Signup and view all the answers

    What is the primary function of ozone in the atmosphere?

    <p>To absorb harmful ultraviolet radiation</p> Signup and view all the answers

    Which statement accurately describes the chemical change related to ozone?

    <p>Ozone absorbs radiation and breaks down to oxygen</p> Signup and view all the answers

    What method is commonly used to prevent rusting on iron articles?

    <p>Covering with a layer of paint or grease</p> Signup and view all the answers

    What process is used to deposit a layer of zinc on iron to prevent rusting?

    <p>Galvanisation</p> Signup and view all the answers

    In which scenario would rusting of iron occur the fastest?

    <p>In a coastal area with high humidity</p> Signup and view all the answers

    What is NOT a factor that contributes to rusting?

    <p>Exposure to ultraviolet light</p> Signup and view all the answers

    Which of the following statements is true about the chemical change associated with ozone?

    <p>Oxygen is a product of ozone breakdown</p> Signup and view all the answers

    Why are iron pipes in homes generally galvanised?

    <p>To prevent rusting</p> Signup and view all the answers

    What effect does saltwater have on rust formation in ships?

    <p>It accelerates the process of rust formation.</p> Signup and view all the answers

    What is the composition of stainless steel?

    <p>Iron mixed with carbon and metals like chromium, nickel, and manganese.</p> Signup and view all the answers

    What type of change is crystallization considered to be?

    <p>A physical change where a pure substance forms from a solution.</p> Signup and view all the answers

    What happens to the solution when copper sulphate is added while heating water?

    <p>It allows for more copper sulphate to dissolve as it heats.</p> Signup and view all the answers

    Why do ships suffer significantly from rusting despite often being made of stainless steel?

    <p>Saltwater increases the rate of rusting on various metal parts.</p> Signup and view all the answers

    What is a characteristic feature of the crystals obtained from evaporating sea water?

    <p>They are small and not pure.</p> Signup and view all the answers

    Which of the following processes primarily involves physical changes?

    <p>Crystallization of substances.</p> Signup and view all the answers

    What must be done to the solution containing copper sulphate before observing the crystals?

    <p>Do not disturb the solution while it cools.</p> Signup and view all the answers

    What type of change is represented by the process of liquified petroleum gas (LPG) transforming from liquid to gas?

    <p>Physical change</p> Signup and view all the answers

    Which process involves a chemical change when burning biogas?

    <p>Combustion of biogas</p> Signup and view all the answers

    Why does rusting of iron occur faster in coastal areas compared to deserts?

    <p>Higher levels of humidity and salt in coastal areas</p> Signup and view all the answers

    What is the role of painting an iron gate in preventing rust?

    <p>It provides a barrier against moisture and oxygen</p> Signup and view all the answers

    Which of the following statements about the gas transformation in LPG is true?

    <p>Both processes A and B are physical changes</p> Signup and view all the answers

    What could be a harmful change resulting from the improper disposal of animal waste?

    <p>Water contamination</p> Signup and view all the answers

    What is the primary outcome of cutting wood into small pieces?

    <p>Physical transformation</p> Signup and view all the answers

    What is the purpose of adding cooking oil to a water sample in the experiment with iron nails?

    <p>To create an oxygen barrier</p> Signup and view all the answers

    Study Notes

    Physical Changes

    • Physical properties of a substance include its shape, size, colour and state.
    • Changes where substances undergo changes in their physical properties are called physical changes.
    • Physical changes are generally reversible; the original substance can be retrieved.
    • No new substance is formed in a physical change.

    Chemical Changes

    • A chemical change results in the formation of a new substance with different properties.
    • Chemical changes are generally irreversible; it is difficult to get back the original substance.
    • Rusting of iron is a common example of chemical change.
    • Rust is iron oxide, which is formed when iron reacts with oxygen and water.
    • Burning, explosion, spoiling of food, neutralization of acid with a base, and the breakdown of ozone are all examples of chemical changes.

    Rusting of Iron

    • Rusting is a chemical change that affects iron articles and slowly destroys them.
    • The process of rusting can be represented by the following equation: Iron (Fe) + Oxygen (O2) + water (H2O) → rust (iron oxide Fe2O3)
    • Rusting requires the presence of both oxygen and water (or water vapour).
    • The higher the moisture content in the air, the faster the rusting process.

    Preventing Rusting

    • Rusting can be prevented by preventing iron articles from coming in contact with oxygen or water, or both.
    • Applying a coat of paint or grease can prevent rusting. These coats should be applied regularly.
    • Depositing a layer of a metal like chromium or zinc on iron, a process called galvanization, also prevents rusting.
    • Stainless steel, which is made by mixing iron with carbon and metals like chromium, nickel, and manganese, does not rust.

    Crystallisation

    • Pure substances can be formed from their solutions through a process called crystallisation.
    • Crystallisation involves allowing a solution to cool slowly, causing the dissolved substance to crystallize out of the solution.
    • It is an example of a physical change.
    • Large crystals of pure substances can be formed through crystallisation.

    Chemical vs. Physical Changes

    • It is important to be able to differentiate between physical and chemical changes.
    • Burning of wood is a chemical change, while cutting wood into small pieces is a physical change.
    • The formation of crystals from a solution is a physical change.
    • Rusting of iron is a chemical change.
    • Painting an iron gate prevents rusting by creating a barrier between the iron and oxygen and water.
    • Rusting is faster in coastal areas than in deserts because of the higher moisture content in the air.
    • The change of LPG from liquid to gas is a physical change, while the burning of the gas is a chemical change.
    • Anaerobic bacteria digesting waste and producing biogas is a chemical change, while burning the biogas is another chemical change.

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    Description

    Explore the differences between physical and chemical changes in substances. This quiz covers key concepts such as properties, reversibility, and examples of each type of change. Understand important processes like rusting and how substances interact.

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