Solubility - Class 6 Notes & Olympiad Questions

Solvent, Solute and Solution

Solvent

a) A solvent is a substance that has the ability to dissolve other substances.
b) It is usually a liquid, but it can also be a gas or a solid in some cases.
c) Solvents have the ability to break apart the particles of a solute and surround them, forming a solution.
d) Common examples of solvents include water, alcohol, and acetone.

Solute

a) A solute is a substance that gets dissolved in a solvent.
b) It can be a solid, liquid, or gas that is added to a solvent.
c) When a solute is added to a solvent, it disperses or dissolves into tiny particles within the solvent.
d) Examples of solutes include sugar, salt, and carbon dioxide.

Solution

a) A solution is a mixture that forms when a solute dissolves in a solvent.
b) It is a homogeneous mixture, which means it has a uniform composition throughout.
c) Solutions can be in different states, such as a solid dissolved in a liquid (e.g., salt water), a gas dissolved in a liquid (e.g., carbonated water), or a gas dissolved in another gas (e.g., air).
d) The solute particles in a solution are evenly distributed and cannot be easily separated from the solvent by filtration.

Water as a Universal Solvent

a) Water is often called a "universal solvent" because it has the ability to dissolve many different substances.
b) Water is made up of tiny particles called molecules. These molecules have a special shape that allows them to interact with other substances and dissolve them.
c) Water can dissolve many things, like sugar, salt, and even some chemicals. That's why we use water to make things like lemonade or tea.
d) Water's ability to dissolve so many things is important for living things. Our bodies are mostly made of water, and water helps carry nutrients and oxygen to our cells.
e) Water also plays a role in the natural purification process as it dissolves and removes pollutants from the environment.
f) It is important to note that everything cannot dissolve in water. Some things, like oil or plastic, don't mix well with water. For those things, we need different solvents.

What is Solubility?

Solubility refers to the ability of a substance to dissolve in another substance, usually a liquid.
In scientific terms, it often refers to the maximum amount of solute that can be dissolved in a given amount of solvent at a specific temperature.

Some key points about solubility are:

Different substances have different solubilities: Some substances dissolve easily in a particular liquid, while others may not dissolve at all or only dissolve to a limited extent.

Solubility is affected by temperature: In general, increasing the temperature of a solvent can increase the solubility of a solute. This means that more of the solute can dissolve in the solvent when the temperature is higher.

"Like dissolves like": Substances with similar chemical properties tend to dissolve in each other. For example, solvents like water can dissolve solutes like salt, sugar more readily, while solvents like oil can dissolve solutes like fats more easily.

Solubility is often expressed as grams of solute per 100 grams of solvent: For example, if you dissolve 20 grams of sugar in 100 grams of water, the solubility of sugar in water would be 20 grams per 100 grams of water.

Some substances have limited solubility: There are solutes that have a maximum amount that can dissolve in a given amount of solvent. This maximum solubility is called the saturation point. When you add more solute beyond the saturation point, it won't dissolve and will instead settle at the bottom or form crystals.

Types of Solutions on the Basis of Solubility

1. Unsaturated Solution

a) This type of solution can dissolve more solute at a given temperature.
b) It means that if you add more solute to the solution, it will still dissolve.
c) There is room for more solute to be dissolved.

2. Saturated Solution

a) In a saturated solution, the maximum amount of solute has been dissolved in the solvent at a given temperature.
b) If you try to add more solute, it will not dissolve. The solution is already holding as much solute as it can at that particular temperature.

3. Supersaturated Solution

a) This is a unique situation where a saturated solution is heated, allowing more solute to dissolve.
b) Then, while the solution is still hot, an additional solute is added, exceeding the normal solubility limit. This creates a supersaturated solution.
c) However, it is a very unstable state, and crystallisation occurs when the solution is cooled or disturbed. The excess solute forms solid crystals.