Review the key concepts, formulae, and examples before starting your quiz.
🔑Concepts
A physical change is a change in which no new substance is formed. Examples include changes in shape, size, state, and the process of soil erosion where the top layer of earth is moved by natural agents like wind and water.
A chemical change is a change in which one or more new substances are formed. Chemical weathering of rocks, such as the reaction with acid rain, is a chemical change.
Rusting is a chemical change that occurs when iron is exposed to oxygen and moisture. The reaction is represented as:
Crystallization is the process of obtaining large crystals of pure substances from their solutions. It is a physical change because no new chemical substance is formed.
Galvanization is the process of depositing a layer of zinc () on iron to prevent rusting, as zinc is more reactive and prevents the iron from coming into contact with air and moisture.
When carbon dioxide () is passed through lime water (), it turns milky due to the formation of calcium carbonate (). This is a chemical change.
📐Formulae
💡Examples
Problem 1:
Explain why the burning of magnesium ribbon is considered a chemical change.
Solution:
Explanation:
When magnesium ribbon burns, it reacts with oxygen in the air to form a new substance, Magnesium Oxide (), which is a white powdery ash. Since a new substance is formed with different properties, it is a chemical change.
Problem 2:
What happens when an iron nail is placed in a solution of copper sulphate? Write the word and chemical equation.
Solution:
Explanation:
Iron () being more reactive than copper () displaces it from the copper sulphate solution. The blue color of the solution changes to green due to the formation of Iron Sulphate (), and a brown deposit of copper is seen on the nail.
Problem 3:
Classify the following as physical or chemical changes: (a) Erosion of soil by water, (b) Reaction between vinegar and baking soda.
Solution:
(a) Physical change, (b) Chemical change.
Explanation:
Soil erosion is a physical change because it involves the mechanical movement of soil particles from one place to another without changing their chemical nature. The reaction between vinegar () and baking soda () is a chemical change because it produces new substances like Carbon Dioxide () and Sodium Acetate.