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Elements, Compounds and Mixtures - Characteristics of Mixtures

Grade 6ICSE

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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A mixture consists of two or more substances (elements or compounds) that are physically mixed together in any proportion, such as a mixture of FeFe (iron) and SS (sulfur).

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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.

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The components of a mixture can be separated by simple physical methods like filtration, evaporation, sublimation, distillation, or magnetic separation.

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In a mixture, there is no fixed composition by mass. For instance, a salt solution can be prepared by dissolving 5 g5\text{ g} or 10 g10\text{ g} of NaClNaCl in 100 ml100\text{ ml} of H2OH_2O.

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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., ΔH=0\Delta H = 0).

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Mixtures do not have fixed melting or boiling points. These temperatures depend on the proportion of the components present in the mixture.

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Mixtures can be classified as Homogeneous (uniform composition throughout, e.g., air) or Heterogeneous (non-uniform composition, e.g., a mixture of oil and H2OH_2O).

📐Formulae

Mass of Mixture=Mass of Component A+Mass of Component B\text{Mass of Mixture} = \text{Mass of Component A} + \text{Mass of Component B}

Percentage of Component=Mass of ComponentTotal Mass of Mixture×100\text{Percentage of Component} = \frac{\text{Mass of Component}}{\text{Total Mass of Mixture}} \times 100

Total Volume≈Volume of Solvent+Volume of Solute\text{Total Volume} \approx \text{Volume of Solvent} + \text{Volume of Solute}

💡Examples

Problem 1:

Identify whether a solution of NaClNaCl in H2OH_2O is a mixture or a compound, and explain why based on its separation.

Solution:

It is a mixture.

Explanation:

A solution of NaClNaCl (salt) in H2OH_2O (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 FeFe filings and SS powder.

Solution:

The FeFe filings are attracted to the magnet, leaving SS behind.

Explanation:

This demonstrates a key characteristic of mixtures: the constituents (Iron, FeFe) retain their individual properties (magnetism). In a compound like FeSFeS (Iron sulfide), the iron would lose its magnetic property.

Problem 3:

Air contains N2N_2, O2O_2, CO2CO_2, 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 CO2CO_2 in industrial areas). 2. Components like O2O_2 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.