How is concentration expressed in mol/dm³?

Concentration in mol/dm³ is expressed as the number of moles of solute per cubic decimetre of solution.

In more detail, concentration is a measure of how much of a given substance (the solute) is mixed with another substance (the solvent). In chemistry, it's often important to know the concentration of a solution, as it can affect the rate of reactions and the properties of the solution. The unit mol/dm³ is commonly used in chemistry to express concentration.

The 'mol' part of the unit stands for moles, which is a standard scientific unit for amount of substance. One mole of a substance contains the same number of entities (such as atoms, molecules, or ions) as there are in 12 grams of carbon-12. This number is known as Avogadro's number, and it's approximately 6.022 x 10²³.

The 'dm³' part of the unit stands for cubic decimetre, which is a unit of volume. One cubic decimetre is equivalent to one litre.

So, when we say that a solution has a concentration of x mol/dm³, we mean that there are x moles of the solute in every cubic decimetre (or litre) of the solution. For example, if a solution has a concentration of 2 mol/dm³, this means there are 2 moles of the solute in every litre of the solution.

To calculate the concentration in mol/dm³, you divide the number of moles of solute by the volume of the solution in dm³. For example, if you have 3 moles of solute in 2 dm³ of solution, the concentration would be 3 ÷ 2 = 1.5 mol/dm³.

Remember, concentration tells us the amount of solute in a specific volume of solution, and it's a crucial concept in many areas of chemistry, including stoichiometry, chemical kinetics, and analytical chemistry.