Make 250 mL of 0.5 M NaCl
Input
Solve for mass; 0.5 M, 250 mL, formula NaCl (58.44 g/mol)
Expected result
7.305 g of NaCl (0.125 mol), made up to 250 mL
Calculators
Molarity Calculator
Solve for molarity, mass, volume or molar mass, plan C1V1 = C2V2 dilutions, and get molar mass from a chemical formula.
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About this tool
The Molarity Calculator solves molarity = mass ÷ (molar mass × volume) for whichever value you are missing: the molarity, the grams of solute, the volume of solution or the molar mass. Pick what to solve for, enter the other three in the units you have (M, mM or µM; g, mg or µg; L, mL or µL), and it returns the answer, the moles of solute and the formula with your numbers substituted. Type a chemical formula such as NaCl, H2SO4, Ca(OH)2 or CuSO4·5H2O to fill in the molar mass from IUPAC standard atomic weights for elements 1 to 36 and common heavier ones such as Ag, I, Ba, Pt, Au, Hg and Pb. Dilution mode solves C1V1 = C2V2 for any one value and tells you how much solvent to add. Results are only as good as your reagent's purity and hydration state, so check the formula weight on the label. Everything runs in your browser.
Why use it
Solves for any one of four values, not just molarity.
Calculates molar mass from a formula, including brackets and hydrates.
Mixes units freely, such as mM with mL, and converts them for you.
Shows the formula with your numbers substituted, so you can check the arithmetic or copy it into a lab report.
Turns a dilution into a plain instruction: how much stock to take and how much solvent to add.
Flags impossible dilutions where the final concentration would exceed the stock.
How to use
- Choose Molarity to work with grams of solute, or Dilution to dilute a stock solution.
- Under Solve for, pick the value you want; that field shows the answer.
- Enter the other values and choose their units from the menus beside them.
- For the molar mass, type the chemical formula, such as CuSO4·5H2O, or type the formula weight from the reagent label.
- Read the result, the moles of solute or the solvent to add, and the worked formula below.
When it helps
- Weighing out solute for a buffer or standard solution of a set molarity.
- Diluting a concentrated stock to a working concentration.
- Checking general chemistry homework or lab-report calculations.
- Finding the molarity of a solution from the mass dissolved and the final volume.
- Working out an unknown compound's molar mass from a solution of known molarity.
Examples
Dilute a stock solution
Input
C1 = 1 M, C2 = 0.1 M, V2 = 100 mL; solve for V1
Expected result
V1 = 10 mL: take 10 mL of stock and add 90 mL of solvent
Molar mass of a hydrate
Input
CuSO4·5H2O
Expected result
249.677 g/mol (Cu 63.546 + S 32.06 + 9 O × 15.999 + 10 H × 1.008)
Tips
- Volume means the final volume of solution: dissolve the solute in less solvent, then top up to the mark in a volumetric flask.
- Use the exact formula on the bottle, including water of crystallization: CuSO4·5H2O (249.677 g/mol) needs far more mass than anhydrous CuSO4 (159.602 g/mol).
- Element symbols are case-sensitive: Co is cobalt, while CO is carbon monoxide.
- For serial dilutions, run dilution mode once per step, using each step's final solution as the next stock.
- Older tables list S as 32.065 and Cl as 35.453; this tool uses IUPAC's current conventional values, so NaCl comes out as 58.440 g/mol rather than 58.443.
Frequently Asked Questions
How do you calculate molarity?
Molarity is moles of solute per liter of solution: M = mass ÷ (molar mass × volume in liters). For example, 5.844 g of NaCl (58.44 g/mol) in 100 mL gives 5.844 ÷ (58.44 × 0.1) = 1 M.
How many grams do I need to make a solution?
Multiply molarity × molar mass × volume in liters. For 250 mL of 0.5 M NaCl: 0.5 × 58.44 × 0.25 = 7.305 g.
How does the dilution mode work?
It uses C1V1 = C2V2: the moles of solute in the stock you take equal the moles in the final solution. Taking 10 mL of a 1 M stock to a final volume of 100 mL gives 0.1 M, so you add 90 mL of solvent.
Which chemical formulas can it read?
Element symbols with counts, nested round or square brackets, and hydrates written with a dot, middle dot or asterisk, such as K4[Fe(CN)6] or CuSO4·5H2O. It covers elements 1 to 36 plus Rb, Sr, Mo, Pd, Ag, Cd, Sn, Sb, I, Cs, Ba, W, Pt, Au, Hg, Pb, Bi and U. Charges and isotope labels are not supported; for anything else, type the molar mass.
Where do the atomic weights come from?
They are IUPAC standard atomic weights rounded to at most four decimals. For elements IUPAC gives as a range, such as hydrogen, carbon, sulfur and chlorine, the tool uses IUPAC's conventional values: 1.008, 12.011, 32.06 and 35.45.
What is the difference between molarity and molality?
Molarity is moles per liter of solution; molality is moles per kilogram of solvent. Molarity shifts slightly with temperature because volume does, while molality does not. This calculator works with molarity.
Can I use millimolar or microliters?
Yes. Each field has its own unit menu: M, mM or µM for concentration, g, mg or µg for mass, and L, mL or µL for volume. The answer appears in the unit chosen for the field you solve.
Why does it say my numbers are not a dilution?
In a dilution the final concentration cannot be higher than the stock, and the final volume cannot be smaller than the stock volume. If your numbers imply either, the stock and final values are probably swapped.
Is anything uploaded?
No. All calculations, including reading the chemical formula, run in your browser.
Explore the category
Glossary
- Molarity (M)
- Concentration in moles of solute per liter of solution; 1 M = 1 mol/L.
- Molar mass
- The mass of one mole of a substance in grams per mole, the sum of the atomic weights in its formula.
- Mole
- The amount of substance that contains 6.02214076 × 10^23 particles.
- Stock solution
- A concentrated solution that is diluted to make working solutions.
- Hydrate
- A salt with water molecules held in its crystal, written with a dot, as in CuSO4·5H2O.
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