Enter the three values you know out of the mass of solute m, the molar mass M, the volume of solution V and the molarity c. The one you leave blank is calculated. Choose a unit for each field (different units are converted automatically).
Table of Contents
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What you can do on this page
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What is this calculation used for?
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How to Use
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Formula
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Symbols and terms
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Good to know before you start
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How to calculate it in Excel
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How to calculate it in Google Sheets
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How to calculate it in Python
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How to write it in LaTeX and other math languages (copy and paste)
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How to have ChatGPT do the calculation
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DataChef Features
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Related Features
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NumberChef Calculators List
What you can do on this page
- Enter any three of the mass of solute \(m\), the molar mass \(M\), the volume of solution \(V\) and the molarity \(c\), and the one you left blank is calculated
- Each field has its own unit (mass: g, mg, kg; volume: L, mL, m³, cm³; molarity: mol/L, mmol/L, μmol/L, mol/m³). Mixed units are converted automatically
- The result always also shows the number of moles of solute (mol) and the mass concentration (g/L)
- Use it directly for lab work and reports, such as "How many grams of salt do I need to make 2 L of 0.5 mol/L salt water?"
- A plain-language explanation of the formulas and copy-and-paste formulas for Excel, Google Sheets and Python are all on this page
What is this calculation used for?
"Make 500 mL of 0.1 mol/L salt water" is one of the first calculations you meet in a school or college lab. The mass you need is mass = molarity × molar mass × volume, so \(0.1 \times 58.44 \times 0.5 \approx 2.92\) g. Weigh this out, dissolve it in water and fill a volumetric flask to exactly 500 mL.
Preparing reagents is part of every chemistry experiment, and this formula is its foundation.
Normal saline, used in IV drips, is 9 g of salt dissolved in water and made up to 1 L (9 g/L, or 0.9%). As a molarity, that is \(9 \div 58.44 \approx 0.154\) mol/L. This concentration is chosen so that its osmotic pressure is about the same as that of body fluids.
Managing the concentrations of IV fluids and drugs in hospitals is built on calculations like this (actual dosing is decided by doctors and pharmacists).
If a juice contains 45 g of glucose (molar mass 180.16 g/mol) per 1 L, its molarity is \(45 \div 180.16 \approx 0.25\) mol/L.
Comparing by grams (mass concentration) makes heavier molecules look like more, but molarity compares how many molecules are dissolved. Sweetness and osmotic pressure depend on the number of molecules, so this view is useful in food design.
Water quality reports often give results in mg/L (a mass concentration), such as "calcium 20 mg/L", and chemists convert these to molarity. For calcium (molar mass 40.08 g/mol), 20 mg/L is \(0.02 \div 40.08 \approx 0.0005\) mol/L, or about 0.5 mmol/L.
Checking against environmental standards and calculating water hardness are built on this conversion.
In hydroponic growing of tomatoes or strawberries, growers manage the fertilizer concentration as the plants grow. For example, dissolving 10.11 g of potassium nitrate (KNO₃, formula mass 101.1) per 1 L gives exactly \(10.11 \div 101.1 = 0.1\) mol/L.
What matters for nutrients is the number of ions, so research and nutrient solution recipes usually manage concentrations in molarity (mmol/L).
Formula
Symbols and terms
Symbols
| \(c\) | see | Molarity: the moles of solute per 1 L of solution. It comes from the first letter of "concentration". (Example - for 0.5 mol/L salt water, \(c = 0.5\) mol/L) |
| \(n\) | en | The number of moles. It counts particles (molecules, ions and so on) with Avogadro's number (about 6.02×10²³) as 1 mol. The unit is mol (mole). |
| \(m\) | lowercase em | The mass of solute, the amount of what you dissolve as measured on a scale. It comes from the first letter of "mass". The unit is g or similar. |
| \(M\) | capital em | The molar mass: the mass of 1 mol of the substance (g/mol). It is the same number as the molecular weight (formula mass). (Example - water is 18.02 g/mol.) Be careful not to mix it up with the lowercase \(m\) (mass). |
| \(V\) | vee | The volume of solution, the volume of the whole liquid after dissolving. It comes from the first letter of "volume". The unit is L, mL or similar. |
| mol/L | moles per liter | The unit of molarity: how many moles are dissolved in 1 L of solution. It is often written with the symbol M, as in "1 M" or "0.5 M", read "molar". This M is not the same as the molar mass symbol \(M\), so be careful. |
| g/mol | grams per mole | The unit of molar mass - how many grams there are in 1 mol. |
| g/L | grams per liter | The unit of mass concentration - how many grams are dissolved in 1 L of solution. This calculator shows it for reference. |
Terms
| mole (mol) | The unit for counting particles. Just as 12 eggs make "1 dozen", about 6.02×10²³ particles (molecules, ions and so on) make "1 mol". Atoms and molecules are far too small to count one by one, but counting them in this huge bundle connects them to grams you can weigh on a scale. |
| number of moles (amount of substance) | An amount measured in mol, based on the count of particles. It is a different quantity from mass (g). Chemical reactions happen between particles, so reaction calculations are basically done in moles, not in grams. Its official SI name is "amount of substance". |
| Avogadro's number (Avogadro constant) | The number of particles in 1 mol, about 6.02×10²³. Precisely, it is defined as the Avogadro constant, 6.02214076×10²³ /mol. |
| molecular weight | How many times heavier one molecule is than 1/12 of a carbon-12 atom (no unit). It is the sum of the atomic weights of the atoms in the molecule; for water (H₂O), 1.008×2 + 16.00 ≈ 18.02. For substances that do not form molecules, such as table salt (NaCl), the same sum is called the formula mass. |
| formula mass | The sum of the atomic weights in the chemical formula of a substance made of ions, such as table salt (NaCl). It is used the same way as the molecular weight (NaCl is 22.99 + 35.45 ≈ 58.44). You can enter a formula mass in the molar mass field on this page. |
| molar mass | The mass of 1 mol of a substance (g/mol). It is the molecular weight (formula mass) with the unit g/mol attached, as in "the molecular weight of water is 18.02 → the molar mass of water is 18.02 g/mol → 1 mol of water is 18.02 g". |
| molarity | A concentration given as moles of solute per 1 L of solution (mol/L). Also called molar concentration. It is the standard concentration in high school chemistry, and its strength is that it connects directly to reaction calculations. |
| mass concentration | A concentration given as grams of solute per 1 L of solution (g/L). It equals the molarity × the molar mass. Food labels and water quality reports often use a related unit, mg/L (≈ ppm). |
| solute | The substance that is dissolved. In salt water, it is the salt. It dissolves in the solvent (water) to make the solution (salt water). |
| solvent | The liquid that does the dissolving. In salt water, it is the water. It dissolves the solute (salt) to make the solution (salt water). |
| solution | The whole mixture of solute + solvent. In salt water, it is the salt water itself. For molarity, you use the volume of the solution. |
| mass percent | A concentration given as the mass of solute as a percentage of the mass of the solution (%). Also called percent by mass. Converting it to molarity needs the density of the solution, so this calculator does not cover it. |
Good to know before you start
Here is what helps you use the calculation on this page with real understanding, not just by pressing the button.
| Unit rates (Grade 6) |
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| Multiplying and dividing decimals (Grades 5–6) |
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| Solutions and concentration (middle school science) |
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| Atoms, molecules and chemical formulas (middle school science) |
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| Moles and molar mass (high school chemistry) |
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How to calculate it in Excel
| Moles of solute n (mol) | 0.5 |
| Volume of solution V (L) | 2 |
| Molarity c (mol/L) | =B1/B2 |
| Mass of solute m (g) | 90 |
| Molar mass M (g/mol) | 18 |
| Moles n (mol) | =B1/B2 |
| Mass of solute m (g) | 100 |
| Molar mass M (g/mol) | 58.44 |
| Volume of solution V (L) | 2 |
| Molarity c (mol/L) | =B1/(B2*B3) |
| Molarity c (mol/L) | 0.5 |
| Molar mass M (g/mol) | 58.44 |
| Volume of solution V (L) | 2 |
| Mass of solute m (g) | =B1*B2*B3 |
| Mass of solute m (g) | 100 |
| Molar mass M (g/mol) | 58.44 |
| Molarity c (mol/L) | 0.5 |
| Volume of solution V (L) | =B1/(B2*B3) |
| Mass of solute m (g) | 100 |
| Molarity c (mol/L) | 0.5 |
| Volume of solution V (L) | 2 |
| Molar mass M (g/mol) | =B1/(B2*B3) |
"=B1/(B2*B3)" means "divide B1 by the product of B2 and B3" ("*" is multiplication and "/" is division).
For example, the first table shows 0.25 (mol/L) in B3, the second 5 (mol) in B3, the third about 0.856 (mol/L) in B4, the fourth 58.44 (g) in B4, the fifth about 3.42 (L) in B4 and the sixth 100 (g/mol) in B4. Just replace the inputs with your own numbers. Enter the values in g, g/mol and L (convert values measured in mg or mL first, using 1 g = 1,000 mg and 1 L = 1,000 mL).
How to calculate it in Google Sheets
| Moles of solute n (mol) | 0.5 |
| Volume of solution V (L) | 2 |
| Molarity c (mol/L) | =B1/B2 |
| Mass of solute m (g) | 90 |
| Molar mass M (g/mol) | 18 |
| Moles n (mol) | =B1/B2 |
| Mass of solute m (g) | 100 |
| Molar mass M (g/mol) | 58.44 |
| Volume of solution V (L) | 2 |
| Molarity c (mol/L) | =B1/(B2*B3) |
| Molarity c (mol/L) | 0.5 |
| Molar mass M (g/mol) | 58.44 |
| Volume of solution V (L) | 2 |
| Mass of solute m (g) | =B1*B2*B3 |
| Mass of solute m (g) | 100 |
| Molar mass M (g/mol) | 58.44 |
| Molarity c (mol/L) | 0.5 |
| Volume of solution V (L) | =B1/(B2*B3) |
| Mass of solute m (g) | 100 |
| Molarity c (mol/L) | 0.5 |
| Volume of solution V (L) | 2 |
| Molar mass M (g/mol) | =B1/(B2*B3) |
How to calculate it in Python
mass = 100.0 # mass of solute m (g)
molar_mass = 58.44 # molar mass M (g/mol), the value for table salt NaCl
volume = 2.0 # volume of solution V (L)
moles = mass / molar_mass # moles n = m ÷ M (mol)
molarity = moles / volume # molarity c = n ÷ V (mol/L)
mass_concentration = mass / volume # mass concentration = m ÷ V (g/L)
print(f"Moles: {moles} mol")
print(f"Molarity: {molarity} mol/L")
print(f"Mass concentration: {mass_concentration} g/L")
# Check by working backward: mass m = c × M × V, volume V = m ÷ (M × c)
mass_check = molarity * molar_mass * volume
volume_check = mass / (molar_mass * molarity)
print(f"Check (mass): {mass_check} g")
print(f"Check (volume): {volume_check} L")
How to write it in LaTeX and other math languages (copy and paste)
c = n ÷ V
c = \dfrac{n}{V}
<math xmlns="http://www.w3.org/1998/Math/MathML" display="block">
<mrow>
<mi>c</mi>
<mo>=</mo>
<mfrac><mi>n</mi><mi>V</mi></mfrac>
</mrow>
</math>
c = n/V
n/V
c := n/V;
c = n/V;
c = n/V
n = m ÷ M
n = \dfrac{m}{M}
<math xmlns="http://www.w3.org/1998/Math/MathML" display="block">
<mrow>
<mi>n</mi>
<mo>=</mo>
<mfrac><mi>m</mi><mi>M</mi></mfrac>
</mrow>
</math>
n = m/M
m/M
n := m/M;
n = m/M;
n = m/M
c = m ÷ (M × V)
c = \dfrac{m}{M V}
<math xmlns="http://www.w3.org/1998/Math/MathML" display="block">
<mrow>
<mi>c</mi>
<mo>=</mo>
<mfrac>
<mi>m</mi>
<mrow><mi>M</mi><mo>⁢</mo><mi>V</mi></mrow>
</mfrac>
</mrow>
</math>
c = m/(M V)
m/(M*V)
c := m/(M*V);
c = m/(M*V);
c = m/(M V)
m = c × M × V
m = c M V
<math xmlns="http://www.w3.org/1998/Math/MathML" display="block">
<mrow>
<mi>m</mi>
<mo>=</mo>
<mi>c</mi>
<mo>⁢</mo>
<mi>M</mi>
<mo>⁢</mo>
<mi>V</mi>
</mrow>
</math>
m = c M V
c*M*V
m := c*M*V;
m = c*M*V;
m = cMV
V = m ÷ (M × c)
V = \dfrac{m}{M c}
<math xmlns="http://www.w3.org/1998/Math/MathML" display="block">
<mrow>
<mi>V</mi>
<mo>=</mo>
<mfrac>
<mi>m</mi>
<mrow><mi>M</mi><mo>⁢</mo><mi>c</mi></mrow>
</mfrac>
</mrow>
</math>
V = m/(M c)
m/(M*c)
V := m/(M*c);
V = m/(M*c);
V = m/(Mc)
M = m ÷ (c × V)
M = \dfrac{m}{c V}
<math xmlns="http://www.w3.org/1998/Math/MathML" display="block">
<mrow>
<mi>M</mi>
<mo>=</mo>
<mfrac>
<mi>m</mi>
<mrow><mi>c</mi><mo>⁢</mo><mi>V</mi></mrow>
</mfrac>
</mrow>
</math>
M = m/(c V)
m/(c*V)
M := m/(c*V);
M = m/(c*V);
M = m/(cV)
How to have ChatGPT do the calculation
You are a molarity calculation assistant. Do the following calculation by actually running Python code, and base your answer only on the numbers from the execution result (do not answer by mental math or guessing). 100 g of table salt (NaCl, molar mass 58.44 g/mol) was dissolved in water and made up to exactly 2 L. Using the molarity formula c = m ÷ (M × V), find each of the following: 1. The molarity of this salt water (mol/L) 2. The number of moles of dissolved salt (mol) 3. The mass of the same salt (g) needed to make 2 L of 0.5 mol/L salt water Show the formulas you used and the numbers from the execution result.
How to Use
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1Enter your numbersType the numbers you want to calculate with into the input fields
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2CalculatePress the "Calculate" button
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3Check the resultThe result appears on the spot. The same page also explains the idea behind the calculation and the formula
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