Changes Around Us: Physical and Chemical - Some Other Processes Involving Chemical Changes
Review the key concepts, formulae, and examples before starting your quiz.
🔑Concepts
Rusting of Iron: It is a chemical change where iron reacts with oxygen and moisture () from the air to form a reddish-brown substance called rust (Hydrated Iron Oxide). Both oxygen and water are essential for rusting.
Prevention of Rusting: Rusting can be prevented by cutting off the contact of iron with air and moisture. Methods include painting, applying grease/oil, and Galvanization (the process of depositing a layer of zinc on iron).
Reaction between Copper Sulphate and Iron: When an iron nail is placed in a blue-colored Copper Sulphate () solution, it turns green due to the formation of Iron Sulphate (). A brown deposit of copper is seen on the nail. This is a displacement reaction.
Reaction between Vinegar and Baking Soda: Vinegar (Acetic acid) reacts with Baking Soda (Sodium Hydrogen Carbonate) to produce Carbon Dioxide () gas and other substances. The presence of is confirmed by passing it through lime water.
Lime Water Test: When gas is passed through lime water (), it turns milky due to the formation of insoluble Calcium Carbonate ().
Burning of Magnesium Ribbon: Burning magnesium in air is a chemical change. It reacts with oxygen to form a white powdery ash called Magnesium Oxide (). When dissolved in water, it forms Magnesium Hydroxide (), which is basic.
Crystallization: It is a process used to obtain large crystals of pure substances from their solutions. Although it involves a change in state/form, it is considered a physical change because no new chemical substance is formed.
📐Formulae
💡Examples
Problem 1:
A student drops an iron nail into a blue solution of Copper Sulphate. After some time, the solution turns green. Explain the chemical change using an equation.
Solution:
The change is a chemical reaction where iron displaces copper from copper sulphate. The green color is due to the formation of Iron Sulphate ().
Explanation:
The chemical equation is: . The blue solution changes to green , and brown copper is deposited on the iron nail.
Problem 2:
Explain why rusting is faster in coastal areas than in deserts.
Solution:
Rusting requires both oxygen and moisture (). Coastal areas have high humidity (water vapor content in air), whereas deserts have dry air.
Explanation:
The presence of salt in coastal water also speeds up the process of rust formation. In a desert, the lack of moisture significantly slows down the reaction: .
Problem 3:
What happens when Carbon Dioxide is passed through Lime Water? Provide the equation.
Solution:
The lime water turns milky because of the formation of Calcium Carbonate.
Explanation:
The reaction is: . The is a white precipitate that makes the solution appear cloudy or milky.