Review the key concepts, formulae, and examples before starting your quiz.
🔑Concepts
A mixture consists of two or more substances (elements or compounds) that are physically mixed together in any proportion, such as a mixture of (iron) and (sulfur).
The constituents of a mixture retain their original physical and chemical properties. For example, in a mixture of iron filings and sulfur, the iron remains magnetic and can be attracted by a magnet.
The components of a mixture can be separated by simple physical methods like filtration, evaporation, sublimation, distillation, or magnetic separation.
In a mixture, there is no fixed composition by mass. For instance, a salt solution can be prepared by dissolving or of in of .
Formation of a mixture does not involve a chemical reaction; therefore, there is no energy change (no heat or light is evolved or absorbed, i.e., ).
Mixtures do not have fixed melting or boiling points. These temperatures depend on the proportion of the components present in the mixture.
Mixtures can be classified as Homogeneous (uniform composition throughout, e.g., air) or Heterogeneous (non-uniform composition, e.g., a mixture of oil and ).
📐Formulae
💡Examples
Problem 1:
Identify whether a solution of in is a mixture or a compound, and explain why based on its separation.
Solution:
It is a mixture.
Explanation:
A solution of (salt) in (water) is a mixture because the salt can be recovered by the physical process of evaporation. Furthermore, the salt retains its salty taste, and the water retains its property of being a liquid, showing that no chemical bond was formed.
Problem 2:
Explain what happens when a magnet is brought near a mixture of filings and powder.
Solution:
The filings are attracted to the magnet, leaving behind.
Explanation:
This demonstrates a key characteristic of mixtures: the constituents (Iron, ) retain their individual properties (magnetism). In a compound like (Iron sulfide), the iron would lose its magnetic property.
Problem 3:
Air contains , , , and other gases. Why is air considered a mixture and not a compound?
Solution:
Air is a mixture because its components can be separated and their ratio varies.
Explanation:
Air is considered a mixture because: 1. Its composition varies from place to place (e.g., more in industrial areas). 2. Components like still support combustion, showing they retain their properties. 3. It can be separated into its constituent gases by physical means like fractional distillation of liquid air.