Guide to calculating Molarity

by Reece
calculating Molarity

Molarity is an important concept in quantitative chemistry. It is the foundation on which many scientists base their experiments on.

In our daily lives, we meet solutions all the time, even in trivial things. For instance, the addition of salt to boiling water to prepare pasta. When the salt dissolves completely, that is a solution right there.

What of our household chemicals? If you look closely at vinegar and bleach, you’ll realize that they are solutions of acetic acids and sodium hypochlorite respectively. We call them solutions because they consist of two components- the solvent and the solute.

What are they?

The solvent is whatever acts as a dissolver, while the solute dissolves. When this happens, a solution is created, regardless of size or quantity. Therefore, it is safe to say that the boiling water is the solvent, while the salt is the solute. The same goes for acetic acid and sodium hypochlorite.

We have mixtures, and we encounter them in our daily lives. For instance, the human body consists of almost 57% water by mass. There are different biological molecules, inorganic ions, and gases that dissolved completely in the water.

There are different kinds of mixtures. If different substances are mixed such that the composition remains the same throughout, then it is a homogenous mixture. If the mixture does not have a uniform composition throughout, it is termed as a heterogeneous mixture.

Another way of describing homogenous mixtures are solutions. Solutions are not monotonous. They can either consist of solids, liquids or gases, as long as the composition remains the same with respect to time.

Now, it is not enough to simply know what mixtures and solutions are, or know they exist, we also have to find a way to quantify the number of species in them. This is where the molar concentration comes in.

Molar concentration

The concentration of a solution indicates the level at which the solute has been dissolved in the solvent. There are several units of concentration, but the standard unit in chemistry is called Molarity, and it is denoted by M.

Molarity, therefore, is the moles of solute for every liter of solution. The mistake a lot of people make is that they think that it’s a mole of solute per liter of solvent. Mind you, molarity is for every liter of solution, and not of solvent alone.

For example, if you add salt to one liter of water, the molarity will no longer be 1 M (it is read as one molar). The solution has to be mixed properly, then the volume has to be taken when it is noticed that the solute has been completely dissolved. The molarity, then, will be calculated when you divide one mole by the total volume taken.

For efficient molarity calculation, you have to divide the number of moles of the solute by the number of liters of solution produced. The unit of the solute differs but the steps remain the same.

If the solute is given in grams, all you have to do is to find the number of moles of that solute using its SI unit. Thereafter, you calculate the total volume and number of moles to get its molarity.

For instance, if you’re asked to find the molarity of a solution that contains about 0.75 mol of NaCl in 4 liters, you obtain the molarity by diving 0.75 mol by 4 liters, which is about 0.1875 M NaCl (remember that molarity is the number of moles for every liter of solution).

Asides the denotation M, molarity has other units such as moles per cubic decimeter (it is denoted by mol/dm3). You can also find mole per liter (mol/l). In some books and research papers, the molar concentration is denoted by placing square brackets around the chemical formula.

This is why you’d often see hydroxide anions denoted like [OH].

Don’t be confused when you see them. Always remember that one cubic decimeter is the same as one liter. They have the same numeric values.

Molarity calculator

While it is very important to know how to calculate the molarity of a solution, why would you go through that stress when you can simply employ a Molarity calculator?

A molarity calculator calculates the molar concentration of a solution using its mass, molecular weight, and volume. The beautiful thing about this calculator is that it’s precise, accurate, timely, and saves you the stress of having to do it yourself.

Fantastic, isn’t it?

This great chemistry tool allows you to calculate the volume of a solution needed to completely dissolve a compound to a given concentration, the concentration of a solution that comes from a mass of compound within a specific volume, and the mass of a compound needed to produce a solution of known concentration and volume.

Wow. How does the molarity calculator work?

Glad you asked.

To get the molarity of a compound, there are four components of the equation- the mass, molecular weight, volume, and molar concentration. Therefore, there are four fields in the calculator.

All you have to do is to input three of these fields and select the required measurement unit.

  1. Volume: This is often given in liters, milliliters, centiliters, and microliters.
  2. Mass: This is often given in grams, micrograms, centigrams, and milligrams.
  3. Concentration: This is often given in molar, Nano molar, micro molar, femtomolar, millimolar, etc. Concentration is one component that can be expressed in several ways, unlike others.
  4. Molecular weight: It is given in g/mol most of the time.

Note that you mustn’t use the molarity calculator to find only concentration. You can find any component at all, provided that you input the values for the other components. For instance, if you want to find volume, you have to put input values for mass, molecular weight, and concentration.


Finding the molarity of compounds hasn’t been easier.

The molarity calculator is here to ease your worries and ensure that you find the right values to conduct your experiments.

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