The Amazing World of Solutes, Solvents, and Solutions - Rusting of Iron and Crystallisation
Review the key concepts, formulae, and examples before starting your quiz.
🔑Concepts
A Solution is a homogeneous mixture of two or more substances. The component present in smaller quantity is the Solute, and the component in larger quantity is the Solvent (e.g., ).
Rusting of Iron is a chemical change that occurs when iron () reacts with oxygen () from the air and moisture ().
The presence of both oxygen and water is essential for rusting. Saltwater accelerates the process of rusting because it increases the conductivity of the electrolyte.
Galvanization is a method of preventing rust by depositing a layer of metal like Zinc () or Chromium () on iron objects.
Crystallisation is a physical change used to purify substances. It involves obtaining large, pure crystals of a substance from its saturated solution.
Stainless steel is made by mixing iron with carbon and metals like chromium (), nickel (), and manganese (); it does not rust.
📐Formulae
💡Examples
Problem 1:
Explain why rusting of iron objects is faster in coastal areas than in deserts.
Solution:
In coastal areas, the air contains a high amount of moisture (humidity) and salts from the sea, which act as catalysts for the reaction.
Explanation:
Rusting requires moisture () and oxygen (). Deserts have low humidity. Furthermore, the presence of salt in coastal water speeds up the formation of .
Problem 2:
How can you obtain pure crystals of Copper Sulphate from an impure sample?
Solution:
By the process of Crystallisation: Add Copper Sulphate powder to boiling water containing dilute until no more solute dissolves. Filter and cool undisturbed.
Explanation:
When the hot saturated solution of cools down, the solubility decreases, and atoms arrange themselves into a highly ordered lattice structure to form pure crystals.
Problem 3:
What happens when an iron nail is placed in a Copper Sulphate () solution?
Solution:
Explanation:
This is a displacement reaction. The blue color of changes to green due to the formation of Iron Sulphate (), and a brown deposit of Copper () is seen on the nail.