The Concentration of a Solution: We talk about the concentration of different solutions throughout our days, such as coffee, juice, etc. Everyone’s definition of concentration is different, and what one may view as highly concentrated may not be the same as another. Adding a solvent or a dense liquid will generally make the liquid more concentrated. So what is the concentration of a solution?
A dilute solution means the quantity of solute is relatively very small, and a concentrated solution implies that the solution has a large amount of solute. But these are relative terms and do not give us the quantitative concentration of the solution. In this article, we will learn about what is meant by the concentration of a solution; we will also see how to find the concentration of a solution and the different methods of expressing the concentration of the solution.
What is the Concentration of a Solution?
There are two parts that exist in an aqueous solution, namely solute and solvent. These are the two basic solution concentration terms that you need to know. It is important to account for the amount of solute in the solution. In chemistry, we define the concentration of solution as the amount of solute in a solvent. When a solution has more solute, we call it a concentrated solution. When the solution has more solvent, we call it a dilute solution.
With this basic understanding of the concept of concentration of the solution, let us look at the different methods of expressing concentration.
Methods of Expressing the Concentration of Solution
There are various methods of expressing the concentration of a solution. You will usually see chemists working with the number of moles. Pharmacists will use percentage concentrations instead of the number of moles. Hence, it is important to understand all the methods of expressing the concentration of solutions.
The concentration of the solution formula is given as follows:
Concentration of solution = Weight of the solute in gram / Volume in Litres
We will also see other methods of calculating the concentration of a solution based on the different methods of expressing concentrations.
Concentration in Parts per Million
It is expressed in terms of weight. The formula for parts per million is given as follows:
ppm(A)= (Mass of A / Total mass of the solution) x1066
Mass Percentage (w/w)
It is expressed in terms of the mass percentage of solute in the solution. The formula for mass percentage is given as follows:
Mass percentage of A= (Mass of component A / Total mass of the solution) x100
e.g. CH3COOH 33% w/w, and H2SO4 98.0% w/w.
Volume Percentage (V/V)
It is expressed in terms of the volume percentage of solute to the solvent. The formula for volume percentage is given as follows:
Volume percentage of A= (Volume of component A / Total volume of the solution) x100
Mass by Volume Percentage (w/V)
Percentage weight in volume expresses the number of grams of solute in 100 ml of product.
Eg: BaCl2 solution 10% w/v, and H2O2 solution 5-7% w/v.
It is the number of moles of solute contained in 1000 ml of solution. It is a commonly used method for expressing concentrations.
Molarity= Mass of solute / Volume of solution in litres
The molality is expressed as the number of moles of a solute contained in 1000 gm of a solvent. The formula for molality is given as follows:
Molality (m)= Mass of solute / Mass of solvent in Kg
We can define it as the number of equivalents of the solute present in the solution, and it is also called equivalent concentration. The formula for normality is given as follows:
Normality (N)= Weight of solute in grams / (Equivalent mass × Volume in litre)
The mole fraction (X) of a component in a solution is defined as the ratio of the number of moles of that component to the total number of moles of all components in the solution. The mole fraction of A is expressed as XA with the help of the following equation in a solution consisting of A, B, and C, we can calculate XA.
XA = moles of A / (mole of A + mole of B + mole of C +….)
Similarly, we can calculate the mole fraction of B, XB with the help of the following formula.
XB = moles of B / (mole of A + mole of B + mole of C +….)
Solutions of Solids in Liquids
Let us discuss Solids in Liquids in the below-mentioned section:
A saturated solution is a solution that remains in contact with an excess of solute.
The amount of solute dissolved per 100g of solvent in a saturated solution at a specific temperature represents the solubility of the solute.
For exothermic substances such as KOH, CaO, Ca(OH)2, M2CO3, M2SO4, etc, solubility is inversely proportional to temperature.
For endothermic substances such as NaCl, KNO3, NaNO3, glucose, etc., solubility is directly proportional to temperature.
Solubility of Gases
The solubility of gases is mostly expressed in terms of the absorption coefficient,k which is the volume of the gas dissolved by unit volume of solvent at 1 atm pressure and a specific temperature.
The solubility of a gas in a liquid depends upon
Temperature Solubility is inversely proportional to temperature as the dissolution of gas is exothermic in most cases.
Nature of Gas – Gases having a higher value of van der Waals force of attraction that is gases that are more easily liquefied are more soluble. For example, SO2 and CO2 are more soluble in water than O2, N2, and H2.
Nature of Solvent – Gases which can ionize in an aqueous solution are more stable in water as compared to the other solvents.
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