Concentration of solutions — Chemistry, 14–17 years
Concentration describes how much dissolved substance is packed into a given volume of solution.
How crowded is the solution?
A solution can look clear while containing very different amounts of dissolved substance. Concentration compares the amount of solute with the volume of solution, often in moles per litre, written mol/L or M. More solute in the same volume means a higher concentration; adding solvent usually makes it lower.
Why concentration matters
A reaction does not depend only on which substances are present; it also depends on how many particles meet in a space. Concentration gives scientists a fair way to compare solutions and prepare a mixture that is safe or reactive enough. That is why laboratory instructions specify both an amount and a final volume.
Calculating a concentration
A student dissolves 0.50 mol of sodium chloride and makes the total solution volume 2.0 L. The concentration formula is c = n ÷ V, where n is moles and V is litres. Substitute the values: c = 0.50 ÷ 2.0 = 0.25 mol/L, or 0.25 M. The final volume, not just the water added, is what belongs in the calculation.
Amount is not concentration
It is easy to think that the container with more dissolved substance must have the higher concentration. That is only true if both containers have the same volume. A large bottle can hold more solute overall but be more dilute, because the same particles are spread through much more solution.
Concentration outside school
Concentration is checked when making medicines, cleaning products and fertilisers, because too little may not work and too much may harm. It is also measured in rivers and drinking water to track pollutants. In each case, the important question is not only what is present, but how much is present in a given volume.
Keep exploring
Other languages
Loading MyLeoNes™…