The best examples of converting grams to moles: 3 practical examples (plus more)

Before we hit the best examples of converting grams to moles: 3 practical examples, let’s lock in the pattern you’ll use every single time.

Every grams-to-moles conversion boils down to one idea:

moles = grams ÷ molar mass

That’s it. The only real work is finding the molar mass from the periodic table.

• Grams tell you how much stuff you physically have on a scale.
• Molar mass (in g/mol) tells you how many grams one mole of that substance weighs.
• Moles tell you how many “chemist dozens” of particles you have (1 mole ≈ 6.022 × 10²³ particles).

Once you see this pattern show up in several real examples of converting grams to moles, the formula stops feeling like a random rule and starts feeling like a unit conversion—just like going from miles to kilometers.

Example 1: Converting grams to moles with water (H₂O)

Let’s kick off our examples of converting grams to moles: 3 practical examples with the world’s favorite molecule: water.

Problem: How many moles are in 36.0 g of water (H₂O)?

Step 1: Find the molar mass of water

Use the periodic table (you can check values at resources like the NIST Chemistry WebBook: https://webbook.nist.gov/chemistry/):

• Hydrogen (H) ≈ 1.01 g/mol
• Oxygen (O) ≈ 16.00 g/mol

Water has 2 H and 1 O:

• H: 2 × 1.01 = 2.02 g/mol
• O: 1 × 16.00 = 16.00 g/mol
• Molar mass of H₂O = 2.02 + 16.00 = 18.02 g/mol

Step 2: Use the grams-to-moles formula

We have 36.0 g of H₂O.

moles of H₂O = (36.0 g) ÷ (18.02 g/mol)

Do the division:

moles of H₂O ≈ 2.00 mol (to three significant figures)

So 36.0 g of water is about 2.00 moles.

This is one of the best examples to start with because the numbers are so tidy that you can see the pattern clearly.

Example 2: Table salt (NaCl) – grams to moles in the kitchen

Next in our examples of converting grams to moles: 3 practical examples, let’s use something you probably have in your kitchen: table salt.

Problem: You have 5.85 g of sodium chloride (NaCl). How many moles is that?

Step 1: Molar mass of NaCl

From the periodic table (for updated values, see https://pubchem.ncbi.nlm.nih.gov/):

• Sodium (Na) ≈ 22.99 g/mol
• Chlorine (Cl) ≈ 35.45 g/mol

Add them:

• Molar mass of NaCl = 22.99 + 35.45 = 58.44 g/mol

Step 2: Convert grams to moles

moles of NaCl = (5.85 g) ÷ (58.44 g/mol)

moles of NaCl ≈ 0.100 mol

So 5.85 g of NaCl is about 0.100 moles.

Fun note: that 0.100 mol is a nice, neat number on purpose—chem teachers love this example because the math is friendly while still feeling realistic.

Example 3: Baking soda (NaHCO₃) – grams to moles in a reaction

For the third of our best examples of converting grams to moles: 3 practical examples, let’s look at baking soda, which shows up in a lot of lab and kitchen experiments.

Problem: A student uses 8.40 g of baking soda (sodium bicarbonate, NaHCO₃) in a reaction. How many moles is that?

Step 1: Molar mass of NaHCO₃

Use average atomic masses:

• Na ≈ 22.99 g/mol
• H ≈ 1.01 g/mol
• C ≈ 12.01 g/mol
• O ≈ 16.00 g/mol (and there are 3 O atoms)

Now add:

• Na: 22.99
• H: 1.01
• C: 12.01
• O: 3 × 16.00 = 48.00

Total molar mass:

Molar mass of NaHCO₃ = 22.99 + 1.01 + 12.01 + 48.00 = 84.01 g/mol

Step 2: Convert grams to moles

moles of NaHCO₃ = (8.40 g) ÷ (84.01 g/mol)

moles of NaHCO₃ ≈ 0.100 mol

Again, 8.40 g of baking soda is about 0.100 moles.

These three core examples of converting grams to moles—water, salt, baking soda—give you a solid pattern. Now let’s widen the lens with more real examples so you can see how this skill shows up in different parts of chemistry.

More real examples of converting grams to moles in everyday chemistry

Those first 3 practical examples are great training wheels, but you’ll see grams-to-moles conversions everywhere: in gas laws, solution chemistry, and especially when you’re finding empirical formulas.

Here are several more real examples of converting grams to moles that connect directly to what you’ll see in class and labs.

Example 4: From grams of glucose to moles (C₆H₁₂O₆)

Glucose is a classic in biochemistry and nutrition.

Problem: A nutrition label says a snack contains 18.0 g of glucose (C₆H₁₂O₆). How many moles of glucose is that?

Step 1: Molar mass of C₆H₁₂O₆

• C: 12.01 g/mol × 6 = 72.06 g/mol
• H: 1.01 g/mol × 12 = 12.12 g/mol
• O: 16.00 g/mol × 6 = 96.00 g/mol

Total molar mass:

Molar mass of C₆H₁₂O₆ ≈ 72.06 + 12.12 + 96.00 = 180.18 g/mol

Step 2: Convert grams to moles

moles of glucose = (18.0 g) ÷ (180.18 g/mol) ≈ 0.100 mol

So 18.0 g of glucose is about 0.100 moles.

This is exactly the kind of calculation that connects chemistry to biology and nutrition. The NIH’s nutrition resources (https://www.nutrition.gov/) often discuss grams of carbs, but chemists think in moles.

Example 5: Oxygen gas (O₂) in a balloon

Now let’s look at a gas, which ties into gas laws you’ll see later.

Problem: A small balloon contains 16.0 g of oxygen gas (O₂). How many moles of O₂ is that?

Step 1: Molar mass of O₂

• O atom ≈ 16.00 g/mol
• O₂ molecule has 2 O atoms: 2 × 16.00 = 32.00 g/mol

Step 2: Convert grams to moles

moles of O₂ = (16.0 g) ÷ (32.00 g/mol) = 0.500 mol

So 16.0 g of O₂ is 0.500 moles.

This kind of grams-to-moles conversion is what you’d use before plugging into the ideal gas law, PV = nRT, where that n is moles.

Example 6: Calcium carbonate (CaCO₃) in an antacid tablet

Antacid tablets often contain calcium carbonate, CaCO₃.

Problem: An antacid tablet contains 1.00 g of CaCO₃. How many moles is that?

Step 1: Molar mass of CaCO₃

• Ca: 40.08 g/mol
• C: 12.01 g/mol
• O: 16.00 g/mol × 3 = 48.00 g/mol

Total:

Molar mass of CaCO₃ ≈ 40.08 + 12.01 + 48.00 = 100.09 g/mol

Step 2: Convert grams to moles

moles of CaCO₃ = (1.00 g) ÷ (100.09 g/mol) ≈ 0.0100 mol

So 1.00 g of CaCO₃ is about 0.0100 moles.

Chemists use this kind of calculation to figure out how much acid a tablet can neutralize. For health-related background on antacids and stomach acid, sites like Mayo Clinic (https://www.mayoclinic.org/) and MedlinePlus (https://medlineplus.gov/) are good references, even if they don’t talk about moles directly.

Example 7: Percent composition to moles – a bridge to empirical formulas

Now let’s connect grams-to-moles to a topic you’re probably studying nearby: empirical formulas.

Imagine a compound that is 27.3 g of carbon and 72.7 g of oxygen in a 100 g sample. These numbers could come from a percent composition problem: 27.3% C and 72.7% O.

Step 1: Treat the percentages as grams

Assume 100 g of the compound:

• 27.3 g C
• 72.7 g O

Step 2: Convert each to moles

For carbon:

• Molar mass of C ≈ 12.01 g/mol
• moles C = 27.3 g ÷ 12.01 g/mol ≈ 2.27 mol

For oxygen:

• Molar mass of O ≈ 16.00 g/mol
• moles O = 72.7 g ÷ 16.00 g/mol ≈ 4.54 mol

Now you’ve used examples of converting grams to moles for each element. From here, you’d divide by the smallest mole value (2.27) to get a ratio:

• C: 2.27 ÷ 2.27 ≈ 1
• O: 4.54 ÷ 2.27 ≈ 2

So the empirical formula is CO₂.

Notice how the entire empirical formula process depends on solid grams-to-moles skills. This is why teachers put so much emphasis on those earlier examples of converting grams to moles: 3 practical examples—they’re the foundation for everything that comes after.

Example 8: From grams to moles in a limiting reactant problem

One more advanced but very typical scenario: limiting reactants.

Consider the reaction:

2 H₂ + O₂ → 2 H₂O

Problem: You react 4.00 g of H₂ with 32.0 g of O₂. How many moles of each reactant do you have?

This is just another pair of grams-to-moles conversions.

For H₂:

• Molar mass H₂: 2 × 1.01 = 2.02 g/mol
• moles H₂ = 4.00 g ÷ 2.02 g/mol ≈ 1.98 mol

For O₂:

• Molar mass O₂: 32.00 g/mol
• moles O₂ = 32.0 g ÷ 32.00 g/mol = 1.00 mol

You’d then compare the mole ratio to the coefficients (2:1) to find the limiting reactant. But notice: you can’t even start that reasoning until you’ve done the grams-to-moles step correctly.

This is why teachers love stacking real examples of converting grams to moles before diving into stoichiometry.

How to think about grams-to-moles so you stop memorizing and start understanding

At this point, you’ve seen several examples of converting grams to moles: 3 practical examples up front and more layered on top. Let’s pull out the mental model that ties them all together.

1. Molar mass is just a conversion factor

Treat molar mass like you’d treat “12 inches per foot” or “2.54 cm per inch.”

• For water, 18.02 g per 1 mol is your conversion factor.
• For NaCl, 58.44 g per 1 mol is your conversion factor.

You’re not doing magic; you’re just switching units.

2. Units should guide your setup

Write the units explicitly:

(grams) × (1 mol / molar mass in g)

You want grams to cancel and moles to remain. If the units don’t cancel correctly, the setup is wrong—no guessing.

3. The periodic table is your best friend

Accurate atomic masses matter. For current, reliable data, chemistry students often use:

• NIST Chemistry WebBook: https://webbook.nist.gov/chemistry/
• PubChem (NIH): https://pubchem.ncbi.nlm.nih.gov/

You don’t need to memorize most atomic masses; you just need to know how to read them and add them.

4. Grams-to-moles is the gateway skill

Whether you’re:

• finding empirical formulas from percent composition,
• calculating how much product forms in a reaction,
• or working with gas laws and solution concentrations,

you will always circle back to grams-to-moles and moles-to-grams. That’s why seeing many examples of converting grams to moles isn’t overkill—it’s training your brain for every topic that follows.

FAQ: Common questions about grams-to-moles conversions

How do I know if I’m doing the grams-to-moles conversion correctly?

Check two things:

• Units: Grams should cancel, leaving moles. If not, flip your fraction.
• Estimate: If your sample is less than the molar mass in grams, you should get less than 1 mole. If it’s more, you should get more than 1 mole. For example, 5.85 g of NaCl is less than 58.44 g/mol, so getting 0.100 mol makes sense.

Can you give a quick example of converting grams to moles for a random compound?

Sure. Say you have 10.0 g of CO₂.

• Molar mass CO₂ = 12.01 + 2(16.00) = 44.01 g/mol
• moles CO₂ = 10.0 g ÷ 44.01 g/mol ≈ 0.227 mol

Same pattern you saw in the earlier examples of converting grams to moles: 3 practical examples—just a different compound.

How does converting grams to moles help with empirical formulas and percent composition?

For empirical formulas, you usually start with either grams or percentages of each element. You:

1. Convert each element’s grams to moles using its molar mass.
2. Divide each mole value by the smallest one to get a simple whole-number ratio.

Without being comfortable with lots of examples of converting grams to moles, this process feels mysterious. Once you are, it’s just a series of familiar steps.

Where can I find reliable atomic masses to use in my calculations?

Your textbook’s periodic table is fine, but if you want current data:

• NIST Chemistry WebBook (U.S. government): https://webbook.nist.gov/chemistry/
• PubChem (NIH): https://pubchem.ncbi.nlm.nih.gov/
• Many university chemistry departments host periodic tables; for example, MIT OpenCourseWare and other .edu sites.

These sources keep atomic masses updated based on international standards.

If you work through these best examples of converting grams to moles: 3 practical examples and the additional ones that follow, you’ll notice something: every new problem starts to look like a remix of the same simple idea. That’s exactly where you want to be in chemistry—seeing patterns, not just memorizing steps.