Concentration of a solution :– The concentration of a solution is the amount of solute present in a given quantity of the solution. In other words the mass of the solute in grams, which is present in 100 g of a solution.
In a solution the relative proportion of the solute and solvent can be varied. Depending upon the amount of solute present in a solution, it can be called a dilute, concentrated or a saturated solution. Different substances in a given solvent have different solubilities at the same temperature.
The most common method for expressing the concentration of a solution, is called percentage method.
The concentration of solution refers to the percentage of solute present in the solution. The percentage of solute can be expressed in terms of -
(i)Concentration of a solution in terms of mass of solute :– If the solution is of a 'solid solute' dissolved in a liquid, then we consider the 'mass percentage of solute' in calculating the concentration of soluton. So, in the case of a solid solute dissolved in a liquid solvent.
Mass by mass percentage of a solution =\( \frac{{Mass\,\,of\,\,solute\,(in\,\,grams)}} {{Mass\,\,of\,\,solution\,(in\,\,grams)}} \times 100 \)
The mass of solution = mass of solute + mass of solvent
Example:1 15 g of methyl alcohol is dissolved in 35 g of water. The weight percentage of methyl alcohol in solution is
(a) 30% (b) 50% (c) 70% (d) 75%
Solution : (a) \( \left( {Weight percentage = \frac{{Weight of solute}} {{Weight of solution}} \times 100} \right) \)
Total weight of solution = (15 + 35) g = 50 g
Weight percentage of methyl alcohol
\( = \frac{{Weightofmethylalcohol}} {{Weightofsolution}} \times 100 = \frac{{15}} {{50}} \times 100 = 30\% \)
(ii) Concentration by mass by volume percentage of a soluiton.
Mass by volume percentage of a solute in - Solution = \( \frac{{Mass\,\,of\,\,solute}} {{Volume\,\,of\,\,solution}} \times 100 \)
Depending upon the unit of the mass and volume, the mass by volume percentage of a solute in solution, can have following units.
(a) gram/ml (b) gram/litre
A solution contains 40g of acetic acid and 500 ml of aq. solution. What is the concentration of acetic acid solution?
Solution : \( \left( {Weight percentage by Volume = \frac{{Weight of solute}} {{Volume of solution}} \times 100} \right) \)
Weight of solute = 40 g
Volume of solution = 500 ml
Weight percentage by volume of acetic acid
\( = \frac{{Weightof\text{acetic acid}}} {{Volumeofsolution}} \times 100 = \frac{{40}} {{500}} \times 100 = 8\% \)