Normality vs. Molarity: What's the Difference?

Let's dive into the fascinating world of chemistry to explore two key concepts: normality vs. molarity. These two terms are often used to express the concentration of solutions, but be careful; they do not mean the same thing. So, what exactly is the difference between normality and molarity, and more importantly, when should they be used?

By the end of this article, you'll have all the keys to distinguish between them easily. Ready to find out? Let's go!

What is molarity?

Molarity, also known as the molar concentration of a solute, is defined by the number of moles of solute present in 1 liter of solution. Molarity is expressed as ${\text{mol}}/{\text{L}}$, abbreviated as $\text{M}$ (pronounced “molar”).

The molarity formula is simple:

where:

• $\text{M}$ — Molarity or molar concentration (in moles per liter, mol/L);
• $\mathrm{n_{solute}}$ — Amount of solute (in moles);
• $\mathrm{V_{solution}}$ — Volume of solution (in liters);
• $\mathrm{m_{solute}}$ — Mass of solute (in grams); and
• $\mathrm{W_{solute}}$ — Molar mass 🇺🇸 of solute (in g/mol).

For example, if you dissolve 2 moles of salt in 1 liter of water, the molarity of the solution is 2 mol/L or 2M (2 molar). Want to calculate molarity in a flash? Use our molarity calculator 🇺🇸!

Molarity is widely used in chemistry because it is simple, direct, and universal. Let's now move on to normality.

What is normality?

Normality, denoted by $\text{N}$, otherwise known as the normal concentration, is a measure of concentration of solute in gram equivalents per volume of the solution. For a solution with "x" grams of solute, the normality equation is:

where:

• $\text{N}$ — Normality (in eq/L);
• $\mathrm{m_{solute}}$ — Mass of solute (in grams);
• $\mathrm{{EW}_{solute}}$ — Equivalent weight of solute; and
• $\mathrm{V_{solution}}$ — Volume of solution (in liters).

Equivalent weight (more precisely, equivalent mass) is the mass of one equivalent, that is, the mass of a given substance which will combine with or displace a fixed quantity of another substance. It's given by:

where:

• $\mathrm{W_{solute}}$ — Molar mass of the solute (in g/mol); and
• $n$ — Valence factor, i.e., number of equivalents per mole (in eq/mol). It's reaction-dependent (e.g., number of H⁺ ions released, OH⁻ ions accepted, or electrons transferred).

For example, for acids, the valence corresponds to the number of H⁺ ions it can release. Take sulfuric acid H₂SO_4, for example. Each H₂SO₄ molecule can release two H⁺ ions in water, so its valence is 2.

Normality is essentially molarity multiplied by the valence factor ($n$). Check out our normality calculator 🇺🇸 to know more about it!

To illustrate further, the molarity and normality of some acids and bases are given below:

The table below highlights the main differences between normality and molarity:

Curious about how molarity compares to molality instead? Check out our Molarity vs. Molality: Understanding the Key Differences for another side-by-side comparison.

To make the normality vs. molarity concept more concrete, let’s examine three practical examples: one for calculating molarity, one for calculating normality, and one for converting between molarity and normality.

Example #1: Calculating molarity

Problem:
You dissolve 10 g of NaOH (molar mass of 40.0 g/mol) in enough water to obtain 500 mL of solution. What is the molarity?

Solution:

1. Calculate the number of moles of solute:

This gives 0.25 moles of solutes.

2. Convert the volume to liters:

3. Substitute the values into the molarity formula:

Answer:
The molarity of the NaOH solution is $\mathrm{0.50 mol/L}$.

Example #2: Calculating normality

Problem:
You dissolve 4.9 g of H₂SO₄ (molar mass of 98.0 g/mol) in enough water to obtain 250 mL of solution. What is the normality for an acid-base reaction in which H₂SO₄ donates 2 H⁺ ions?

Solution:

1. Find the equivalent weight:

2. Convert the volume to liters:

To simplify your volume conversion, don't hesitate to use our volume converter 🇺🇸.

3. Apply the normality formula:

Answer:
The normality of the H₂SO₄ solution is $\mathrm{0.40 eq/L}$.

Example #3: Converting between molarity and normality

Problem:
A solution of H₂SO₄ has a molarity of 1.5 M. What is its normality for complete acid-base dissociation?

Solution:

1. Identify the valence factor. We know that H₂SO₄ releases 2 H⁺ ions, so $n=2$.
2. Apply the molarity to normality formula:

Answer:
A 1.5 M H₂O₄ solution is $\mathrm{3.0\ N}$ in this reaction.

What you should remember from this normality vs. molarity comparison is that, while molarity indicates the number of moles of solute present in a liter of solution, normality focuses on the number of reactive equivalents per liter, which depends on the type of reaction. It's important that you know the difference between normal vs. molar concentrations in order to choose the appropriate measurement for your work.