Amount of Substance

Solutions

Solutions

A homogeneous mixtures of two or more substances in which the substance proportions are the same throughout the mixture is known as a solution. The solvent is the major component of a solution. In the majority of causes the solvent used is water.

  • The solutes are the minor components.

The concentration of the solution is the solute quantity within a fixed amount of solvent or solution. This is usually measured as either:

  • grams of solute per dm3 of solution
  • moles of solute per dm3 of solution (this is also called the molarity of the solution)

The number of moles of solute (n), the molarity of the solution (V), and the volume of solution (C) are related through the following equation:

n = C x V

The volume must be measured in dm3 or litres. If measured in cm3 then V/100 rather than V must be used.

If the concentration is in gdm-3 then it needs to be converted into molarity before using it in the above equation. This can be achieved using the following formula:

Cg = Cm x mr

In which:

  • C = concentration (measured in gdm-3)
  • Cm = molarity
  • mr = molar mass

Using this equation it is possible to work out the volume of one solution needed to react with another solution for which the volume is known.

It is important to remember that you need to convert all quantities into moles before making a comparison.

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Titration

Volumetric analysis is the quantitative investigation of chemical reactions in which reacting volumes are compared. Reacting volumes can be determined through the process of titration.

This procedure involves taking a solution which has an unknown concentration and titrating it against another solution of a known concentration. The former solution is put into a conical flask while the latter is put into a burette.