Mixtures

A mixture is a substance in which two or more substances are mixed without a chemical reaction between them. The substances retain their original properties and can be separated from the mixture if need be. For example – a bowl of cereals mix, cookie dough, salt mixed in water, carbon dioxide in coke, a tossed salad etc. Air is the most common mixture around us.

CHARACTERISTICS OF MIXTURES

1. HOMOGENEOUS MIXTURE –

A homogenous mixture is a mixture that has the same proportion of the component substances throughout. The constituents are distributed uniformly in a homogeneous mixture. It has visibly indistinguishable parts. It can be a solid, liquid or a gaseous mixture. Examples –

  • Air is a homogeneous mixture of gaseous substances like nitrogen, oxygen and other substances.
  • Saline solution is a homogeneous mixture of water and salt.
  • Most alloys are homogenous mixtures of elements, that has a characteristic of a metal and at least one of the components is a metal. For e.g. steel is an alloy of iron and carbon.

2. HETEROGENEOUS MIXTURE –

A heterogeneous mixture is not blended together and do not have the same consistency throughout. They are non-uniform in their composition and we can see multiple distinguishable parts in it. Examples –

  • A mixture of sand and water.
  • A mixture of oil and water.
  • A mixture of salt and pepper.
  • A chocolate chip cookie – one bite may have more chocolate than the next.

Classification of Mixtures Based on Particle Size

Let’s take three glass beakers, each filled half with water. To the first beaker, we add some sugar, to the second some chalk powder and some milk in the third and mix all of them well. Let’s switch off the light and pass a beam of light through each beaker.

  1. The first beaker with sugar would be clear and we won’t be able to see the path of light as the sugar particles have dissolved and cannot scatter light. Such mixtures are known as SOLUTIONS.

A solution is a homogeneous mixture composed of two or more substances. It is commonly used for liquid state of matter, but solutions of gases and solids are also possible. It consists of a solute and a solvent. A solute is a substance dissolved in the solution and solvent is the substance in which the solute is dissolved. In a solution of saline water, salt is the solute and water is the solvent. 

  1. Chalk is insoluble in water and hence the beaker would have VISIBLE chalk particles suspended in water that would scatter the beam of light and we see the path of light. Such mixtures are known as SUSPENSIONS.

A suspension is a heterogeneous mixture in which solute particles do not dissolve but are suspended in the solvent and float around freely in it. The particles suspended are big enough to scatter light and they eventually settle down by the process of sedimentation. 

  1. The third beaker with milk will also scatter the light passing through it although the mixture looks even with no visible particles in it. Such mixtures are known as COLLOIDS.

Colloids exhibit properties intermediate between those of suspensions and solutions. They are small enough to keep afloat and not settle. At the same time they are big enough to scatter light. This makes the path of light visible. They are usually cloudy or opaque. Colloids can be in solid, liquid or gaseous media. Examples of colloids include smoke (solid in gas), ink (solid in liquid), some gems (solid in solid) among others.

 

Check Point

  1. The two characteristics of mixtures are __________ and __________.
  2. Air is an example of a ___________ mixture.
  3. The particle size in a solution are _______ than the particles in a suspension mixture.
  4. A mixture of water and milk is an example of a _________.
  5. A pack of M&Ms is an example of a _______________ mixture.

Answer Key

  1. Homogeneous and heterogeneous
  2. Homogeneous
  3. Smaller
  4. Colloid
  5. Heterogeneous