A solution is a homogeneous mixture of two or more substances. Lemonade, soda water etc. are all examples of solutions.

(i) A solution of sugar in water is a solid in liquid solution. In this solution, sugar is the solute and water is the solvent.

(ii) A solution of iodine in alcohol known as ‘tincture of iodine’, has iodine (solid) as the solute and alcohol (liquid) as the solvent.

(iii) Aerated drinks like soda water etc., are gas in liquid solutions. These contain carbon dioxide (gas) as solute and water (liquid) as
solvent.

(iv) Air is a mixture of gas in gas. Air is a homogeneous mixture of a number of gases. Its two main constituents are: oxygen (21%) and nitrogen (78%). The other gases are present in very small quantities.

`color{green}("𝐂𝐨𝐦𝐩𝐨𝐧𝐞𝐧𝐭𝐬 𝐨𝐟 𝐬𝐨𝐥𝐮𝐭𝐢𝐨𝐧:")`


`color{red}("𝟏 𝐒𝐨𝐥𝐮𝐭𝐞:")` The component of the solution that is dissolved in the solvent (usually present in lesser quantity) is called the solute.

`color{red}("𝟐 𝐒𝐨𝐥𝐯𝐞𝐧𝐭:")` The component of the solution that dissolves the other component in it (usually the component present in larger amount) is called the solvent.

`color{green}("𝐏𝐫𝐨𝐩𝐞𝐫𝐭𝐢𝐞𝐬 𝐨𝐟 𝐬𝐨𝐥𝐮𝐭𝐢𝐨𝐧:")`


`color{green}(•)` A solution is a homogeneous mixture.

`color{green}(•)` The particles of a solution are smaller than `color{red}("1 nm" (10^(-9) "metre)")` in diameter. So, they cannot be seen by naked eyes.

`color{green}(•)` Because of very small particle size, they do not scatter a beam of light passing through the solution. So, the path of light is not visible in a solution.

`color{green}(•)` The solute particles cannot be separated from the mixture by the process of filtration. The solute particles do not settle down when left undisturbed, that is, a solution is stable.

Depending upon the amount of solute present in a solution, it can be called a dilute, concentrated or a saturated solution.

`color{green}("𝐒𝐀𝐓𝐔𝐑𝐀𝐓𝐄𝐃 𝐒𝐎𝐋𝐔𝐓𝐈𝐎𝐍 :")` At any particular temperature, a solution that has dissolved as much solute as it is capable of dissolving, is said to be a saturated solution. In other words, when no more solute can be dissolved in a solution at a given temperature, it is called a saturated solution.

`color{green}("𝐒𝐎𝐋𝐔𝐁𝐈𝐋𝐈𝐓𝐘:")` The amount of the solute present in the saturated solution at this temperature is called its solubility.

`color{green}("𝐔𝐍𝐒𝐀𝐓𝐔𝐑𝐀𝐓𝐄𝐃 𝐒𝐎𝐋𝐔𝐓𝐈𝐎𝐍:")` If the amount of solute contained in a solution is less than the saturation level, it is called an unsaturated solution.

`color{red}("𝐃𝐢𝐟𝐟𝐞𝐫𝐞𝐧𝐭 𝐬𝐮𝐛𝐬𝐭𝐚𝐧𝐜𝐞𝐬 𝐢𝐧 𝐚 𝐠𝐢𝐯𝐞𝐧 𝐬𝐨𝐥𝐯𝐞𝐧𝐭 𝐡𝐚𝐯𝐞 𝐝𝐢𝐟𝐟𝐞𝐫𝐞𝐧𝐭 𝐬𝐨𝐥𝐮𝐛𝐢𝐥𝐢𝐭𝐢𝐞𝐬 𝐚𝐭 𝐭𝐡𝐞 𝐬𝐚𝐦𝐞 𝐭𝐞𝐦𝐩𝐞𝐫𝐚𝐭𝐮𝐫𝐞.")`


The concentration of a solution is the amount of solute present in a given amount (mass or volume) of solution, or the amount of solute dissolved in a given mass or volume of solvent.

`color{green}("𝐂𝐨𝐧𝐜𝐞𝐧𝐭𝐫𝐚𝐭𝐢𝐨𝐧 𝐨𝐟 𝐬𝐨𝐥𝐮𝐭𝐢𝐨𝐧 = 𝐀𝐦𝐨𝐮𝐧𝐭 𝐨𝐟 𝐬𝐨𝐥𝐮𝐭𝐞/ 𝐀𝐦𝐨𝐮𝐧𝐭 𝐨𝐟 𝐬𝐨𝐥𝐮𝐭𝐢𝐨𝐧 𝐎𝐫 𝐀𝐦𝐨𝐮𝐧𝐭 𝐨𝐟 𝐬𝐨𝐥𝐮𝐭𝐞/𝐀𝐦𝐨𝐮𝐧𝐭 𝐨𝐟 𝐬𝐨𝐥𝐯𝐞𝐧𝐭")`


There are various ways of expressing the concentration of a solution.


(i) `" Mass by mass percentage of solution"`

`color{red}(= "Mass of solute"/"Mass of solution" xx 100)`

(ii) `"Mass by volume percentage of a solution"`

`color{red}(= "Mass of solute"/"Volume of solution " xx 100)`

A suspension is a heterogeneous mixture in which the solute particles do not dissolve but remain suspended throughout the bulk of the medium.

`color{green}("𝐏𝐑𝐎𝐏𝐄𝐑𝐓𝐈𝐄𝐒 𝐎𝐅 𝐒𝐔𝐒𝐏𝐄𝐍𝐒𝐈𝐎𝐍")`

`color{green}(•)` Suspension is a heterogeneous mixture.

`color{green}(•)` The particles of a suspension can be seen by the naked eye.

`color{green}(•)` The particles of a suspension scatter a beam of light passing through it and make its path visible.

`color{green}(•)` The solute particles settle down when a suspension is left undisturbed, that is, a suspension is unstable. They can be separated from the mixture by the process of filtration.

Solutions in which the size of particles lies in between those of true solutions and suspensions are called colloidal solutions.

`color{green}("𝐂𝐎𝐌𝐏𝐎𝐍𝐄𝐍𝐓𝐒 𝐎𝐅 𝐂𝐎𝐋𝐋𝐎𝐈𝐃𝐀𝐋 𝐒𝐎𝐋𝐔𝐓𝐈𝐎𝐍𝐒:")`

(1) Dispersed phase

(2) Dispersion medium

The solute-like component or the dispersed particles in a colloid form the dispersed phase, and the component in which the dispersed phase is suspended is known as the dispersing medium.

Colloids are classified according to the state (solid, liquid or gas) of the dispersing medium and the dispersed phase.


`color{green}("𝐏𝐑𝐎𝐏𝐄𝐑𝐓𝐈𝐄𝐒 𝐎𝐅 𝐂𝐎𝐋𝐋𝐎𝐈𝐃𝐀𝐋 𝐒𝐎𝐋𝐔𝐓𝐈𝐎𝐍𝐒")`

`color{green}(•)` A colloid is a heterogeneous mixture.

`color{green}(•)` The size of particles of a colloid is too small to be individually seen by naked eyes.

`color{green}(•)` Colloids are big enough to scatter a beam of light passing through it and make its path visible.

`color{green}(•)` They do not settle down when left undisturbed, that is, a colloid is quite stable.

`color{green}("𝐓𝐘𝐍𝐃𝐀𝐋𝐋 𝐄𝐅𝐅𝐄𝐂𝐓")`

`color{green}(•)` The scattering of a beam of light by colloidal particles is called the Tyndall effect after the name of the scientist who discovered this effect.

`color{green}(•)` Tyndall effect can also be observed when a fine beam of light enters a room through a small hole. This happens due to the scattering of light by the particles of dust and smoke in the air.

`color{green}(•)` Tyndall effect can be observed when sunlight passes through the canopy of a dense forest. In the forest, mist contains tiny droplets of water, which act as particles of colloid dispersed in air.