Compounds and Mixtures

Compound is a pure substance made up of two or more elements in a chemical combination. The combinations are always in a fixed ratio. Examples of compounds are carbon dioxide and water.

Mixture is a physical combination of two or more substances in any ratio. It can also be defined as a substance which consists of two or more elements or compounds not chemically combined together. Examples of mixtures are sand and water, oil and water.

Differences between mixtures and compounds

Compounds Mixtures
The constituent elements cannot be separated by physical methods. The components can be separated from one another by physical methods.
Chemical changes are involved when compounds are formed. No chemical change occurs when mixtures are formed.
The components cannot be seen separately. Components may be seen separately.
They have always fixed composition by mass of the elements. Mixtures may vary in composition.
The properties of compounds are very different from those of the individual elements. The properties of mixtures are those of the individual components.

MIXTURES

Types of Mixtures

There are two types of mixtures,
  1. Homogeneous mixture
  2. Heterogeneous mixture
Homogeneous mixture is the mixture which has uniform composition throughout it. It has also uniform appearance and physical properties.
Examples of homogeneous mixtures are
  1. mixture of salt and water
  2. mixture of sugar and water.
Heterogeneous mixture is the mixture which has different composition, appearance and properties at various points in the mixture.
Examples of heterogeneous mixtures are mixtures of
  1. sand and water
  2. iron and sulphur
Generally mixtures can be
  1. Solid-solid mixture eg. salt and sugar
  2. Solid-liquid mixture eg. sand and water
  3. Liquid-liquid eg. ethanol and water

  1. SOLID-SOLID MIXTURES

    2. Here a solid substance is mixed with another solid substance.

    Some solid substances are melted and mixed together then allowed to cool.

    If this involves metals to metals or metals and non-metals, the resulting mixture is called alloy.

    Alloy is a homogeneous mixture of two or more metals or of metals and non-metals.

    Examples of alloys
    Alloy Composition
    Brass Copper + zinc
    Bronze Copper + tin
    Stainless steel Iron + chromium + nickel

  2. SOLID-LIQUID MIXTURES

    3. Here a solid substance is mixed with another substance which is in liquid state.

    1. SOLUTION

      2. Solution is a homogeneous mixture of two or more substances which are solute and solvent.

      Solute is the substance that dissolves in solvent while solvent is the substance that dissolves solute.

      Solvent is the component of the solution that is present in large amount in a solution.

      SOLUTE + SOLVENT → SOLUTION
      Examples of solutions

      Types of solutions

      Unsaturated solution is a solution that can dissolve more solute at a given temperature.

      Saturated solution is a solution that can dissolve no more solute at a given temperature.

      Super saturated solution is a solution that contains more solutes than it can hold at a given temperature.

      Applications of saturation


      Classification of solutions into three states of matter

      Solutions do not have to be solids dissolved in liquids, but it can be mixtures of various states of matter.

      Gaseous solution example air, water gas and producer gas

      Solid solution example all alloys such as brass, bronze and stainless steel

      Liquid solution example ethanol in water, petrol and kerosene

      There are two types of solvents
      • polar solvent
      • non-polar solvent.
      Substance can dissolve into these solvents according to the simple rule ‘like dissolves like’.

      NOTE
      Water is said to be universal solvent because it dissolves many substances than any other solvent known.

      Uses of solvents

    2. SUSPENSION

      3. A suspension is a liquid containing small particles of solids which are spread throughout it and the solid particles settle on standing.

      or

      Suspension is the heterogeneous mixture where solid particles are dispersed throughout a liquid and can settle at the bottom of container if left undisturbed.

      Examples are
      1. muddy and water
      2. sand and water
      3. chalk powder and water

      Differences between suspension and solution

      Solutions Suspensions
      They are homogeneous mixtures. They are heterogeneous mixtures.
      They are transparent or clear. They are opaque or not clear.
      Solute particles completely dissolved in a solvent. Solute particles settle if the suspension is undisturbed.
      Components can be separated by evaporation. Components can be separated by filtration.

    3. COLLOIDS

      4. Colloid is the mixture where very small particles of one substance are evenly spread throughout another substance.

      Colloids appear very similar to solutions but the components in colloids are not dissolved in each other.

      Colloid is also similar to suspension but the difference being that the particles in colloids do not settle at the bottom even when left undisturbed.

    Some examples of colloids are

    1. SOL - colloid in which small solid particles are suspended in a liquid for example paint, ink and blood.
    2. EMULSION – colloid in which liquid particles are spread throughout another liquid eg. milk
    3. GELS – colloid in which a liquid is dispersed throughout a solid eg. jelly.
    4. AEROSOL- colloid in which solid or liquid particles suspended in gas eg. smoke, fog and clouds
    5. FOAM- colloid in which gas particles are dispersed throughout a liquid or solid eg. shaving cream, lather.

  3. LIQUID-LIQUID MIXTURES

There are two types of liquid – liquid mixtures Examples of immiscible liquids are
  1. water and kerosene
  2. water and cooking oil
  3. water and petrol
immiscible liquids