Classification of matter - Solutions - Content of solutions - Solubility

  Classification of matter - Solutions - Content of solutions - Solubility

Classification of matter(figure 1.1)

1.1

Pure substances and mixtures:

They can be distinguished into pure substances and mixtures.

Pure or specified substances:

They are those which, regardless of how they are prepared, have a definite composition and properties.

E.g. water (H2O), sugar, alcohol, oxygen (O2), iron (Fe) are pure substances

Mixtures:

They have a variable composition depending on the method of preparation and their origin.

Most of the substances we encounter are mixtures, the composition of which varies e.g. milk, oil, sea water.

Chemical compounds:

They are pure substances that can be broken down into other simpler ones and consist of at least two types of atoms (individuals with different atomic numbers).

Homogeneous and heterogeneous mixtures:

Homogeneous Mixtures (solutions):

They are homogeneous mixtures, i.e. they have the same composition and the same properties throughout their extent.

Characteristic of homogeneous mixtures is that we can not distinguish their components. For example, in seawater we can not distinguish salt.

Heterogeneous mixtures:

 They are non-uniform, i.e. they do not have the same composition throughout.

In these mixtures we distinguish several times their ingredients and their different properties, e.g. oil with water.

The homogeneous parts of a mixture are called phases.

Solution:

It is a homogeneous mixture of two or more substances, which are the components of the solution.

Solvent:

Of these components, the one that has the same physical state as the solution and is usually in excess is called a solvent. 

Dissolved substances:

The other components of the solution are called dissolved substances.

Solutions are divided into gases, liquids and solids. 

Molecular solutions:

 The solute is in the form of molecules.

Ionic or electrolytic solutions:

They contain the solute in the form of ions.

Content:

 Expresses the amount of solute contained in certain percentages of solution.

Many times we use the terms dense and sparse for solutions of relatively high or relatively low content, respectively.

The content of a solution is usually expressed in the following ways:

1. Percentage by weight (% w / w) 

The (% w / w) content expresses the mass (in g) of the solute in 100 g of solution.

2. Percentage by weight (% w / v) 

The% w / v content expresses the mass (in g) of the solute in 100 mL of solution.

3. Content in percent volume by volume (% v / v).

The% v / v content expresses the volume (in mL) of the solute in 100 mL of solution.

Soluble:

Has high solubility

Insoluble:

Has low solubility.

Solutions that contain the maximum amount of solute are called saturated solutions.

Solutions that contain less than the maximum amount of solute are called unsaturated.

The solubility of a substance is affected by the following factors:

a. the nature of the solvent

Here the general rule "the like dissolves the same" applies. This means that solvent and solute must have similar chemical structure (eg molecular or ionic composition).

b. temperature

Usually the solubility of solids in water increases with increasing temperature, while the solubility of gases in water decreases with increasing temperature.

c. pressure

In general, the solubility of gases in water increases with increasing pressure. Therefore, as soon as we open a bottle of carbonated beverage (the pressure decreases and becomes equal to atmospheric), the solubility of CO2 in water decreases and the beverage foams.