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ChemistryEdu Logo Solution | Concentration Terms#

Concentration Terms#

  • Concentration Terms are used to express the amount of solute dissolved in a solvent.
  • There are different concentration terms like mass percentage, volume percentage, mass by volume percentage, parts per million, molarity, molality, mole fraction
  • We will discuss each one of them in detail.

Mass Percentage(w/w)#

Mass percentage of a component of a solution is defined as:

\[w/w = {Mass\ of\ component \times 100 \over Total\ mass\ of\ solution}\]

If 10 gram sugar is present in 90 gram water, find its mass percentage.

Here, the mass of solution is (10+90) grams = 100 grams.

\[w/w = {Mass\ of\ component \times 100 \over Total\ mass\ of\ solution}\]
\[= {10 \times 100 \over 100}\]
\[= {10}\]

Volume Percentage(v/v)#

Volume percentage of a component of a solution is defined as:

\[v/v = {Volume\ of\ component \times 100 \over Total\ volume\ of\ solution}\]

If 10 ml sugar is present in 90 ml water, find its volume percentage.

Here, the volume of solution is (10+90) ml = 100 ml.

\[v/v = {Volume\ of\ component \times 100 \over Total\ volume\ of\ solution}\]
\[= {10 \times 100 \over 100}\]
\[= {10}\]

Mass by Volume Percentage(w/v)#

Mass by volume percentage of a component of a solution is defined as:

\[w/v = {Mass\ of\ component \times 100 \over Total\ volume\ of\ solution}\]

If 10 grams sugar is present in 100 ml solution, find its volume percentage.

Here, the volume of solution is = 100 ml.

\[w/v = {Mass\ of\ component \times 100 \over Total\ volume\ of\ solution}\]
\[= {10 \times 100 \over 100}\]
\[= {10}\]

Parts per million(ppm)#

  • When solute is present in very small amount, we express its concentration in terms of parts per million.

ppm is calculated using the following formula:

\[ppm = {n \times 10^6 \over N}\]

where, n = Number of parts of component

and, N = Number of parts of all components of solution

  • Parts per million can be expressed as mass to mass, volume to volume and mass to volume.

Parts per billion (ppb)#

parts per billion(ppb) is defined as:

\[ppb = {n \times 10^9 \over N}\]

where, n = Number of parts of component

and, N = Number of parts of all components of solution

  • Similar to ppm, parts per billion(ppb) is also used when solute is in a very small amount.

Mole Fraction (Χ)#

  • For a solution consisting of A as solute and B as solvent, we define mole fraction of A present in the solution as:
\[Χ_A = {n_A \over n_A + n_B}\]

where, nA = Moles of A

and, nB = Moles of B

  • Similarly, mole fraction of B in the solution is defined as:
\[Χ_B = {n_B \over n_A + n_B}\]
  • Here, we can see that:
\[Χ_A + Χ_B = 1\]
  • Similarly, for a solution containing k components, we can write:
\[Χ_1 = {n_1 \over n_1 + n_2 + n_3 +\ ..... +\ n_k}\]
\[Χ_2 = {n_2 \over n_1 + n_2 + n_3 +\ ..... +\ n_k}\]
\[Χ_3 = {n_3 \over n_1 + n_2 + n_3 +\ ..... +\ n_k}\]

Similarly,

\[Χ_k = {n_k \over n_1 + n_2 + n_3 +\ ..... +\ n_k}\]

And,

\[Χ_1 + Χ_2 + Χ_3 +\ ......\ + Χ_k = 1\]

Molarity(M)#

  • Molarity is defined as number of moles of solute present in one litre of solution.
\[M = {n_{solute} \over V_{solution} (L)}\]
  • Since molarity is dependent on volume, it changes with change in temperature.

Molality(m)#

  • Molality is defined as number of moles of solute present in one kilogram of solvent.
\[m = {n_{solute} \over mass_{solvent} (Kg)}\]
  • Molality does not change with change in temperature.