Question

1. give an example of each of the following: a) a heterogeneous mixture – b) a homogeneous mixture – c) an element – d) a compound – e) a physical property – f) a physical change – g) a chemical property – h) a chemical change – i) a solution –

Explanation:

• a) Heterogeneous mixture: A mixture with non - uniform composition. For example, a salad with lettuce, tomatoes, and cucumbers. The different components are visible and not uniformly distributed.
• b) Homogeneous mixture: A mixture with uniform composition throughout. For example, salt dissolved in water. The salt particles are evenly distributed in the water and the mixture has the same properties in all parts.
• c) Element: A substance that cannot be broken down into simpler substances by chemical means. For example, oxygen ($O_2$). It is made up of only oxygen atoms.
• d) Compound: A substance made up of two or more different elements chemically combined in a fixed ratio. For example, water ($H_2O$), which is made from hydrogen and oxygen in a 2:1 ratio by moles.
• e) Physical property: A property that can be observed or measured without changing the substance's chemical identity. For example, the density of gold. We can measure density without changing gold into another substance.
• f) Physical change: A change in which the substance's chemical identity remains the same, only its physical state or appearance changes. For example, melting ice. Ice (solid water) changes to liquid water, but it is still $H_2O$.
• g) Chemical property: A property that describes a substance's ability to undergo a chemical reaction and form new substances. For example, the flammability of methane. Methane can react with oxygen to form carbon dioxide and water.
• h) Chemical change: A change in which a new substance is formed. For example, burning wood. Wood (mainly cellulose) reacts with oxygen to form carbon dioxide, water, and ash (new substances).
• i) Solution: A homogeneous mixture of a solute and a solvent. For example, sugar dissolved in coffee. The sugar (solute) is evenly distributed in the coffee (solvent).

Answer:

• a) Heterogeneous mixture: Salad (lettuce, tomatoes, cucumbers)
• b) Homogeneous mixture: Salt - water solution
• c) Element: Oxygen ($O_2$)
• d) Compound: Water ($H_2O$)
• e) Physical property: Density of gold
• f) Physical change: Melting ice
• g) Chemical property: Flammability of methane
• h) Chemical change: Burning wood
• i) Solution: Sugar dissolved in coffee