We’ll start at the very beginning so you can understand molar concentration in its infancy. Let’s say you have a glass of soda and a vase full of water on your window sill. Both of these substances exist, but they are not a pure material. Every substance has a mixture of different compounds. Organisms especially are complex, with multiple different elements making up a person or animal.
In molar concentration in chemistry, there are two kinds: homogeneous and heterogeneous.
Homogeneous mixtures contain even compounds with one phase of matter. They are a solution that can be gas, liquid, or solid. You may not always be able to separate the components, such as air, steel, or sugar water.
A heterogeneous mixture contains a whole host of elements. They may all have different properties, and you may be able to separate them. Take, for example, pizza, the ocean, and concrete. When you take a sample of any of these, they will not contain the same measures of compounds.
If you work with chemicals, you’ll be familiar with the parameter known as concentration. Concentration is the measurement of a dissolved substance in a set volume. Concentration is the most common term, but another one is molar concentration.
When you operate with molar concentrations, express your findings in mole units. When you do, you can express chemical reactions with integers, combining the totals at the end.
A mole is many things. It’s a pigment-producing skin cell, a burrowing animal, and a spy. In the realm of science, it’s a measurement for substance. The symbol for mole is ‘mole,’ meaning something has many different elementary entities.
When you use mole as a unit, you must specify what particles are in use – such as ions, atoms, and electrons.
The molar mass of carbon is 12, meaning there are 12 grams per mole. You also need to replace the “substance” component of the mole formula with the name of the substance in use. You must always use a precise specification of the units so that others can follow the same methods.
When talking about the definition of mole, you’ll also find that it changes depending on the year. For example, in 2019, mole became a quantity of a chemical substance with 6.02214076*10²³ particles. The particles can be atoms, ions, electrons, or anything related.
That strange figure, 6.02214076*10²³ is Avogadro’s constant with a symbol of L or Na. Avogadro’s constant is convenient when working with chemical reactions and substance weights. For example, with this value, you can now read the mole value from the periodic table.
It’s as easy as linking the number of entities (X) in a sample N (X) and the sample volume containing substances.
n (X) = N (X) / NA
N (X) has no dimensions, and n (X) uses the mole unit.
Above, we mentioned molar concentration. Molarity is the same thing, with the symbol M. Molarity is how you express a solution’s concentration. You get your answer by defining the volume of moles in a solution or substance.
The concentration = the number of moles / the volume
By using the following formula, you can find a solution’s molarity.
The molarity = the concentration / the molar mass
You show the answer in density (g/l or g/mL).
The mass of one mole in a solution is the molar mass. You express it in grams per mole, with it being a constant property of a substance.
While you’re using our molarity calculation to work out the molar mass, you can also use it to find a substance’s mass.
The mass / volume = the concentration = the molarity x the molar mass
Mass = the substance’s mass in grams
Volume = the solution’s total volume in liters
Did you know you can also use molarity for calculating a solution’s dilution? It’s a concept with many uses!
You can recognize molarity units as moles per cubic decimeter. They appear as mol/dm3 and M (molar). You can also abbreviate the molar concentration with square brackets around the solute. If you browse through any old books with molar solutions, you will see moles per liter (mol/l) a lot. One liter equals one cubic decimeter.
Before moles were acceptable for quantities of chemical substances, chemists used other methods. They would offer concentrations with the weight of the solute/volume. That’s now less common than moles.
Throughout quantity measurements in solutions, you may find both molarity and molality used. The two terms are not interchangeable. Molality has a lowercase m, whereas molarity uses M. We will cover how this works below.
If you want to understand how our molarity calculator works, follow these steps below. You can learn how to calculate molarity.
1. Choose your substance. For this example, we’ll use nitric acid.
2. Identify the molar mass of your substance. Nitric acid is equal to 63.01 g/mol.
3. Work out your substance’s mass concentration. Enter it into the concentration section. Otherwise, enter your mass and solution volume. Let’s say you have ten grams in a two-liter volume.
4. Get your molarity formula
The mass / the volume = the molarity x the molar mass
The mass / (the volume x the molar mass) = the molarity
5. Substitute the values you know to get your molarity.
Molarity = 158.705 for nitric acid at 10 grams in two liters.
Whenever you are working with both molality and molarity, you have to take care. The two words are similar but have different meanings. Both also express a solution’s concentration.
Molarity describes a substance’s amount in a solution per unit volume. Molality, on the other hand, describes the substance’s amount of the solvent’s unit mass. It's also a solute’s number of moles, or dissolved material per unit of a solvent.
That doesn’t mean the two terms don’t work together. You can change molarity to molality or molarity to molality.
The molarity = (the molality x the solution’s mass density) / (1 + (the molality x the solution’s molar mass)
How are you supposed to find a concentration of a solution you don’t know? It’s unlikely such a situation will arise, but it’s helpful to know how to tackle it if it does. If you need a solution’s concentration, you can use the titration technique.
This technique gets its concentration from the chemical reaction of a known solution. You add the titrant (the solution you know) to a measured quantity of your unknown solution. Wait until the reaction ends, then measure the titrant volume.
In three short steps, you can use the titration method to find molarity.
1. Put the solution you know into a flask, with the titrant in a burette.
2. Mix the concentrations until the reaction ends. Observe any changes.
3. Use the titration formula to calculate molarity.
With a ratio of 1:1 for the solutions, the formula is:
The acid molarity x the acid volume = the molarity of the base x the volume of the base
If you are not using a ratio of 1:1, you would change the formula.
