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Nature of Matter: Elements, Compounds, and Mixtures - Metals and Non-metals

Grade 8CBSE

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

🔑Concepts

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Matter is classified into pure substances (elements and compounds) and impure substances (mixtures).

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Elements are pure substances consisting of only one type of atom, classified into metals, non-metals, and metalloids.

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Metals are generally hard, lustrous, malleable (can be beaten into thin sheets), ductile (can be drawn into wires), and are good conductors of heat and electricity.

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Non-metals are generally soft (except diamond), non-lustrous, brittle, and poor conductors of heat and electricity.

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Metals react with oxygen (O2O_2) to form basic oxides, such as Magnesium Oxide (MgOMgO).

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Non-metals react with oxygen to form acidic or neutral oxides, such as Sulfur dioxide (SO2SO_2).

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A more reactive metal displaces a less reactive metal from its salt solution; this is known as a displacement reaction.

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Compounds are substances formed by the chemical combination of two or more elements in a fixed ratio by mass, such as water (H2OH_2O) and carbon dioxide (CO2CO_2).

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Mixtures consist of two or more substances physically mixed in any proportion, maintaining their individual properties.

📐Formulae

2Mg+O2→2MgO2Mg + O_2 \rightarrow 2MgO

MgO+H2O→Mg(OH)2MgO + H_2O \rightarrow Mg(OH)_2

S+O2→SO2S + O_2 \rightarrow SO_2

SO2+H2O→H2SO3 (Sulfurous acid)SO_2 + H_2O \rightarrow H_2SO_3 \text{ (Sulfurous acid)}

Fe+CuSO4→FeSO4+CuFe + CuSO_4 \rightarrow FeSO_4 + Cu

2Al+6HCl→2AlCl3+3H2↑2Al + 6HCl \rightarrow 2AlCl_3 + 3H_2 \uparrow

4Fe+3O2+xH2O→2Fe2O3⋅xH2O (Rust)4Fe + 3O_2 + xH_2O \rightarrow 2Fe_2O_3 \cdot xH_2O \text{ (Rust)}

💡Examples

Problem 1:

What happens when a copper vessel is exposed to moist air for a long time? Provide the chemical equation.

Solution:

2Cu+H2O+CO2+O2→Cu(OH)2+CuCO32Cu + H_2O + CO_2 + O_2 \rightarrow Cu(OH)_2 + CuCO_3

Explanation:

When copper is exposed to moist air, it acquires a dull green coating. This green material is a mixture of copper hydroxide (Cu(OH)2Cu(OH)_2) and copper carbonate (CuCO3CuCO_3).

Problem 2:

Identify the type of reaction: Zn(s)+CuSO4(aq)→ZnSO4(aq)+Cu(s)Zn(s) + CuSO_4(aq) \rightarrow ZnSO_4(aq) + Cu(s) and explain why it occurs.

Solution:

Displacement Reaction.

Explanation:

Zinc (ZnZn) is more reactive than Copper (CuCu). Therefore, Zinc displaces Copper from its salt solution, Zinc Sulfate (ZnSO4ZnSO_4), resulting in the blue color of CuSO4CuSO_4 fading.

Problem 3:

Explain the nature of the product formed when phosphorus burns in oxygen and reacts with water.

Solution:

The product is Phosphorus pentoxide (P4O10P_4O_{10}), which forms Phosphoric acid (H3PO4H_3PO_4) in water, making it acidic.

Explanation:

Non-metals like phosphorus react with oxygen to form acidic oxides. When these oxides dissolve in water, they form acids that turn blue litmus paper red.