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Nature of Matter: Elements, Compounds, and Mixtures - What Are Minerals?

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 mixtures based on their chemical composition.

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Elements are pure substances consisting of only one type of atom, such as Gold (AuAu), Iron (FeFe), or Oxygen (O2O_2).

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Compounds are substances formed when two or more elements combine chemically in fixed proportions by mass. For example, Water (H2OH_2O) always contains Hydrogen and Oxygen in a 2:12:1 atomic ratio.

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Mixtures consist of two or more substances physically combined in any proportion. They can be homogeneous (e.g., Salt solution) or heterogeneous (e.g., Sand and water).

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Minerals are naturally occurring, inorganic solid substances with a definite chemical composition and an ordered crystalline structure. Most minerals are compounds, such as Quartz (SiO2SiO_2) and Calcite (CaCO3CaCO_3).

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A mineral from which a metal can be extracted easily and profitably is called an Ore. For example, Hematite (Fe2O3Fe_2O_3) is an ore of Iron.

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The chemical formula of a compound represents the number of atoms of each element present in one molecule of that compound.

📐Formulae

H2O (Water)H_2O \text{ (Water)}

NaCl (Common Salt / Sodium Chloride)NaCl \text{ (Common Salt / Sodium Chloride)}

SiO2 (Quartz / Silicon Dioxide)SiO_2 \text{ (Quartz / Silicon Dioxide)}

CaCO3 (Calcium Carbonate)CaCO_3 \text{ (Calcium Carbonate)}

Fe2O3 (Hematite / Iron Oxide)Fe_2O_3 \text{ (Hematite / Iron Oxide)}

Al2O3⋅2H2O (Bauxite / Aluminium Ore)Al_2O_3 \cdot 2H_2O \text{ (Bauxite / Aluminium Ore)}

💡Examples

Problem 1:

Calculate the total number of atoms present in 3 molecules of Calcium Carbonate (CaCO3CaCO_3).

Solution:

Total atoms = 3×(1 atom of Ca+1 atom of C+3 atoms of O)=3×5=153 \times (1 \text{ atom of } Ca + 1 \text{ atom of } C + 3 \text{ atoms of } O) = 3 \times 5 = 15 atoms.

Explanation:

One molecule of CaCO3CaCO_3 contains 11 Calcium atom, 11 Carbon atom, and 33 Oxygen atoms. For 33 molecules, we multiply the sum of atoms by 33.

Problem 2:

A sample of a mineral weighs 500500 grams. If it contains 125125 grams of pure Iron, calculate the percentage of Iron in the mineral sample.

Solution:

Percentage of Iron=Mass of IronTotal Mass×100\text{Percentage of Iron} = \frac{\text{Mass of Iron}}{\text{Total Mass}} \times 100 Percentage=125500×100=25%\text{Percentage} = \frac{125}{500} \times 100 = 25\%

Explanation:

The percentage composition is calculated by dividing the mass of the specific element by the total mass of the compound/mixture and multiplying by 100100.

Problem 3:

Identify whether the following are Elements, Compounds, or Mixtures: (a) Diamond (CC), (b) Sea Water, (c) Baking Soda (NaHCO3NaHCO_3).

Solution:

(a) Element, (b) Mixture, (c) Compound.

Explanation:

Diamond is made only of Carbon atoms (CC), so it is an element. Sea water contains various salts and water physically mixed, making it a mixture. Baking soda has a fixed chemical formula (NaHCO3NaHCO_3), making it a compound.