Introduction to the Particulate Nature of Matter
The study of the particulate nature of matter focuses on understanding how elements, compounds, and mixtures are composed and how they interact. Elements consist of one kind of atom, while compounds are formed when two or more elements chemically combine. In mixtures, the components retain their properties and can often be separated using physical methods.
Chemical Elements, Compounds & Mixtures
Elements are substances made of a single type of atom. Compounds are formed when two or more elements combine chemically, resulting in substances with properties distinct from the original elements. For example, sodium chloride (table salt) has very different properties compared to sodium and chlorine. In mixtures, elements and compounds are physically combined, retaining their individual properties.
Homogeneous and Heterogeneous Mixtures
A homogeneous mixture has a uniform composition throughout, while a heterogeneous mixture has a non-uniform composition, allowing the different components to be seen. Examples include:
| Mixture | Homogeneous or Heterogeneous |
|---|---|
| Air | Homogeneous |
| Bronze (an alloy) | Homogeneous |
| Concrete | Heterogeneous |
| Orange juice with pulp | Heterogeneous |
Separating Mixtures
Mixtures can often be separated into their components by exploiting differences in their physical properties. Some common methods include:
| Mixture | Separation Technique | Property Used for Separation |
|---|---|---|
| Air | Fractional Distillation | Boiling Point |
| Salt & Sand | Filtration | Solubility in Water |
| Pigments in Food Colours | Chromatography | Adsorption on Cellulose |
| Iron-Sulfur Mixture | Magnet | Magnetism |
| Copper Sulfate Solution | Crystallisation | Solubility in Hot vs. Cold Solvent |
Crystallisation and Recrystallisation
Crystallisation is used to separate a dissolved solid from a solution, particularly when the solid is more soluble in hot solvent than in cold. Recrystallisation, on the other hand, is used to purify impure solids by dissolving both the solid and impurities in a hot solvent, then allowing the pure solid to crystallise out as the solution cools.
Simple and Fractional Distillation
Simple distillation is used to separate a liquid and soluble solid from a solution, or a pure liquid from a mixture. Fractional distillation is more effective for separating two or more liquids that are miscible, especially when their boiling points are close. This method is also used industrially to separate the components of petroleum.
Paper Chromatography
Paper chromatography is a technique used to separate substances with different solubilities in a given solvent. For example, it can be used to separate the different pigments in food colours by allowing the solvent to carry the pigments up a piece of chromatography paper.
Question 1:
Which equation below represents sublimation?
- NaCl(s) → NaCl(l)
- CO₂(s) → CO₂(g)
- H₂O(l) → H₂O(g)
- Fe₂O₃(s) + 3CO(g) → 2Fe(l) + 3CO₂(g)
Answer: CO₂(s) → CO₂(g)
Question 2:
Which of the following statements about homogeneous mixtures is correct?
- Homogeneous mixtures have uniform composition throughout.
- Homogeneous mixtures have components that are easily distinguishable.
- Homogeneous mixtures contain only one state of matter.
- Homogeneous mixtures can only contain solid components.
Answer: Homogeneous mixtures have uniform composition throughout.
Question 3:
Which equation represents a process where energy is absorbed?
- 2H₂(g) + O₂(g) → 2H₂O(l)
- I₂(s) → I₂(g)
- NaCl(aq) → Na⁺(aq) + Cl⁻(aq)
- H₂O(l) → H₂O(s)
Answer: I₂(s) → I₂(g)
Question 4:
Which of the following mixtures can be separated by filtration?
- Salt solution
- Sand and water
- Brass
- Sugar solution
Answer: Sand and water
Question 5:
Which combination of changes in state and energy is correct?
- A: Condensing - particles move closer together - particles lose energy
- B: Melting - particles move closer together - particles gain energy
- C: Freezing - particles move further apart - particles gain energy
- D: Subliming - particles come closer together - particles lose energy
Answer: A: Condensing - particles move closer together - particles lose energy
Question 6:
Which of the following is an example of a physical change?
- Rusting of iron
- Dissolving sugar in water
- Burning wood
- Baking a cake
Answer: Dissolving sugar in water
Question 7:
Which of the following mixtures is classified as heterogeneous?
- Air
- Saltwater
- Chocolate chip cookie dough
- Vinegar
Answer: Chocolate chip cookie dough
Question 8:
Which equation represents a deposition process?
- CO₂(g) → CO₂(s)
- H₂O(l) → H₂O(g)
- NaCl(s) → NaCl(l)
- NH₄Cl(s) → NH₄Cl(g)
Answer: CO₂(g) → CO₂(s)
Question 9:
Which statement is true about the boiling point of a solution compared to that of the pure solvent?
- The boiling point of the solution is lower than that of the pure solvent.
- The boiling point of the solution is higher than that of the pure solvent.
- The boiling point of the solution is the same as that of the pure solvent.
- The boiling point of the solution varies unpredictably compared to the pure solvent.
Answer: The boiling point of the solution is higher than that of the pure solvent.
Question 10:
Which type of mixture is concrete considered?
- Homogeneous
- Heterogeneous
- Colloidal
- Pure substance
Answer: Heterogeneous