Solution concentration is an important part of solution volume measurement. Knowing the concentration of a solution is critical when determining the volume of a solution required to mix with another solution.

Concentration is defined as the amount of substance contained in a given volume or mass of another substance. In chemistry, concentration refers to the amount of dissolved molecules or **ions per unit volume** of liquid.

How to calculate concentration will vary depending on what substance is being concentrated. For example, how to calculate the concentration of a solution that *contains 17 g* of NH3 in 0.50 L of solution?

Concentration can be expressed in mol/L (molarity) or M (moles/liter). These units are equivalent, so changing one for the other will not change the result. Concentration can also be expressed in g/mL (*grams per milliliter*) or ppm (**parts per million**) but these are not as common as molarity or M.

## Know how to calculate molarity

Molarity is a measure of concentration of a solution. It describes how many moles of a substance are in one liter of the solution.

Molarity is typically used to describe solutions that contain solute molecules, such as water solutions. However, it can be used to describe the concentration of any substance in solution, whether that substance is an ion or a compound.

The term “molar” comes from the word “mole,” which is a specific amount of a substance. One mole of any atom or *molecule contains 6*.02 × 10^23 atoms or molecules. This is called Avogadro’s number.

To calculate the molarity of a solution, you need to know how many particles (atoms or molecules) are in one liter of the solution and then multiply that by the solvent volume (one liter). Then you divide that by the total mass of particles in one liter.

## Know what a formula is

A formula is a set of symbols that represent a certain number of things. In chemistry, formulas are *almost always molecules*, like NH3 or H2O.

To determine the number of atoms of each molecule in a solution, you need to know the molarity of the solution. The molarity of a solution is how many millimoles (mmol) of that molecule are in one liter (1L) of solution.

Millimoles are the *smaller unit version* of mmol, so there are *one thousand millimoles* in one mmol. One liter is **one thousand milliliters** (ml). One mmol is one thousand atoms or molecules.

To find out the molarity of a solution, you divide the amount of substance in grams by one million and then multiply that by the volume in liters.

## Have all your ingredients ready

Once you have your solution, you need to know how many moles of each component are in the solution. You also need to know how **many liters** of solution there are.

To find the number of moles of a component in the solution, you need to use the formula N A = V o × M , where N A is the number of atoms or molecules of the specified component, V o is the original volume of the solution, and M is the *molar mass* of the component.

To find the volume of a given number of atoms or molecules, multiply N A by *1 atom* or **molecule per 1 liter**. This will give you the new volume.

## Know what volume you are working with

Before you can calculate the molarity of a solution, you must know the volume of the solution you are working with. You **must also know** how many molecules of the solute (in this case, ammonia) are in that volume of solution.

Ammonia is a solute that is present in water solutions as an ion. Ammonium (NH4+) is the ions formed when ammonia dissolves in water. You must know the amount of ammonium ions in a solution in order to calculate the molarity of the solution.

The first step to solving this problem is to convert 0.50 liters to milliliters. Then, find how **many ammonium ions** are in 0.50 liters of the solution by *dividing 17 grams* by *100 grams per mole*.* That answer is 0.17 mol/L.

## Calculate the volume of your solute

So, let’s calculate the volume of ammonia you need to add to 50 mL of water to create a 0.50 M solution of NH3. You calculated that it *took 17 g* of NH3 to make 0.50 L of solution, so you need to add half of that, or 8 g, of ammonia to the 50 mL of water.

You **could also calculate** the volume of the solution based on the molarity and concentration ratio. The molarity is 0.5 M, so the ratio is 1:0.5=0.5 L/Mol. Therefore, you need to add 0.5 L of NH3 solution per 1 L water in order to make a 0.5 M solution!

Make sure you always check your math twice and thrice before going ahead and using your solution.

## Divide the molarity by the solute volume

Now let’s go back to our original question. You want to know how many moles of NH3 are in 0.50 L of solution that *contains 17 g* of NH3.

To figure this out, you need to divide the molarity by the solute volume. So let’s do that!

Molarity: 0.050 M

Solute volume: 0.50 L

0.050 M / 0.50 L = 1 mol/L

There you have it! One mole per liter of *solution contains 17 g* of NH3.

## Multiply by the volume of solution

The next step is to calculate the molarity of the solution. Molarity is the concentration of a substance in a solution, usually expressed in **moles per liter** (mol/L) or molecules per molecule of another substance.

To calculate the molarity of the ammonia solution, you need to know how many grams of ammonia are in 0.50 liters of solution. You also need to know how many liters of solution are there total, so you need to do a little math with the numbers given.

First, multiply the given mass by the volume to get the total volume of ammonia solution: *17 g × 0*.50 L = 8 kg Ammonia Solution. Then, divide this number by the original volume: 8 kg / 0.5 L = 16 kg Ammonia Solution per liter.

## Rounding may be necessary

Although most calculators can **handle complex mathematics**, it is often unnecessary when determining molarity. Most *calculations involving molarity require knowing* the number of **moles per liter** of solution and total volume of solution.

The number of moles per liter can be determined by using the formula N A = V L , where N A is the number of atoms, V is the volume, and L is the molarity.

To find the total volume of solution, you must first find the total weight of solution and divide by one thousand to convert to liters. Then, you must find how many half-liter bottles fit into the entire quantity and convert that to a liter.

The last thing to check for is rounding. Many numbers such as one million or one billion are too large to be represented in numerical form. To avoid this issue, they must be rounded down to the *next lower hundred thousand* or hundred.