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Methods of Expressing Concentration

As a qualitative expression of concentration, we always use the words diluted or concentrated when referring to a solution.
As a qualitative expression of concentration, we always use the words diluted or concentrated when referring to a solution. As the term dilute implies, the very little solute is present, and as the term concentrated implies that there is a substantial amount of solute present. A qualitative concentration is derived from this, but bear in mind that this is a relative concentration.

A liquid composition is considered to be a "concentration" when it refers to its volume or concentration. As it pertains to volume or concentration, "concentration" defines the amount or amount of a substance in a fluid. So, we commonly describe levels of various solutions in the surroundings as follows to quantify their concentration:

Concentration (C or S)
A liter of solution contains how many solute molecules.

C or S = Weight of solute in grams / Volume in liters

Mass percentage (w/w)
By dividing the mass of one component in the solution by the concentration, one can calculate mass percentages. Component A in a solution comprises solute and solvent B. In this case, their mass percentage is determined by:

Mass % of A = Mass of component A in the solution / Total mass of the solution × 100

Volume percentage (v/v)
Often, concentration is expressed by the volume percentage of one of the components in the solution. This form is called volume percentage and is as follows:

volume% of A = Volume of component A in the solution / Total volume of the solution × 100

Molarity (M)
Molarity(M): It can be expressed in terms of moles (gram molecular weights) or molarity (molecular weight) as the number of moles (gram molecular weights) that can be dissolved in 1000 ml (1 liter).

Molarity (M) = number of moles of solute / Number of liters of solution
Or
Molarity (M) = (Number of moles of solute / Number of mL of solution) X 1000
Or
Number of moles of solute = Molarity (M) X Number of liters of solution

Molality (m)
There are many ways to determine the solubility of a solute -- the molality(m) measures how many moles of a solute is dissolved in one kilogram of a solvent.

Molality (m) = Number of solute moles / Number of kilograms (kg) of the solvent present

Normality (N)
Normality (N): Normally, the number of equivalent solutes per liter makes up a solution's normality(N).
Normality (N) = number of gram equivalents of solute / Number of liters of the solution
Or
Number of gram equivalents of solute = Normality X Number of liters of the solution

Formality (F)
The solid intensity (F) of a solution can be expressed in grams formula weight (GFW) per liter of solvent.

Formality (F) = GFW/Litres of solution.

Percent w/w (%w/w)
A 100-gram sample contains 100 grams of solutes, which is a relative weight to weight measure.

Percent w/v (%w/v)
100 grams of solute is expressed as grams in 100 milliliters of the product.
(i.e., 100 ml of solution). e.g., H2O2 solution 5-7% w/v.

Percent v/v (%v/v)
The volume of a solute in 100 milliliters of product is expressed as a percent by volume.

Percent v/w (%v/w)
It is a measure of milliliters of solute per one kilogram of product and is expressed as (% volume by weight).

Part per million (ppm)
When parts per million (ppm) are used to express the concentration of a solution, it means that the weight of each gram is accounted for, unless otherwise stated. PPM measures how many parts per million (PPM) of solute there are in 10,000,000 grams of solution. Example - The limit test for chloride was 25 parts per million of chloride.

ppm(A)=Mass of A / Total mass of the solution×10,000,000

It is commonly used to express concentration in solution or to formulate titrations. Still, it has one major disadvantage: it is based on molecular weight divided by the volume of the solution, and volume is determined by density. In situations where the temperature is a key factor, such as 40°C or 0°C, the molarity of a solution may differ by several percent from its initial value. In the case of volumetric glassware, a specific temperature is used, usually 20°C. The error may not be an issue in many applications, but in cases where precision is essential, the errors become problematic. Although mole fractions, molalities, and mass fractions of a solution are dependent on temperature and influenced by the mass of the solute and solvent, each is independent of its temperature.
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Ankur Choudhary is India's first professional pharmaceutical blogger, author and founder of Pharmaceutical Guidelines, a widely-read pharmaceutical blog since 2008. Sign-up for the free email updates for your daily dose of pharmaceutical tips.
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