Molarity Calculator
Use this calculator to determine the molarity, moles of solute, or volume of a solution. Simply enter any two known values, and the calculator will solve for the third.
function calculateMolarity() {
var molesInput = document.getElementById('moles');
var volumeInput = document.getElementById('volume');
var molarityInput = document.getElementById('molarity');
var volumeUnitSelect = document.getElementById('volumeUnit');
var resultDiv = document.getElementById('molarityResult');
var molesStr = molesInput.value;
var volumeStr = volumeInput.value;
var molarityStr = molarityInput.value;
var volumeUnit = volumeUnitSelect.value;
var moles, volumeLiters, molarity;
var fieldsFilled = 0;
// Parse and validate Moles
if (molesStr !== ") {
moles = parseFloat(molesStr);
if (isNaN(moles) || moles < 0) {
resultDiv.innerHTML = "Please enter a valid positive number for Moles.";
return;
}
fieldsFilled++;
}
// Parse and validate Volume, convert to Liters
if (volumeStr !== '') {
var rawVolume = parseFloat(volumeStr);
if (isNaN(rawVolume) || rawVolume < 0) {
resultDiv.innerHTML = "Please enter a valid positive number for Volume.";
return;
}
volumeLiters = (volumeUnit === 'mL') ? rawVolume / 1000 : rawVolume;
fieldsFilled++;
}
// Parse and validate Molarity
if (molarityStr !== '') {
molarity = parseFloat(molarityStr);
if (isNaN(molarity) || molarity < 0) {
resultDiv.innerHTML = "Please enter a valid positive number for Molarity.";
return;
}
fieldsFilled++;
}
if (fieldsFilled < 2) {
resultDiv.innerHTML = "Please fill in at least two of the three fields (Moles, Volume, Molarity) to perform a calculation.";
return;
}
// Determine which value to calculate
if (molarityStr === '') { // Calculate Molarity
if (moles === undefined || volumeLiters === undefined) {
resultDiv.innerHTML = "Error: Moles or Volume missing for Molarity calculation.";
return;
}
if (volumeLiters === 0) {
resultDiv.innerHTML = "Volume cannot be zero.";
return;
}
molarity = moles / volumeLiters;
resultDiv.innerHTML = "Calculated Molarity:
" + molarity.toFixed(4) + " M (mol/L)";
} else if (molesStr === ") { // Calculate Moles
if (molarity === undefined || volumeLiters === undefined) {
resultDiv.innerHTML = "Error: Molarity or Volume missing for Moles calculation.";
return;
}
moles = molarity * volumeLiters;
resultDiv.innerHTML = "Calculated Moles of Solute:
" + moles.toFixed(4) + " mol";
} else if (volumeStr === ") { // Calculate Volume
if (moles === undefined || molarity === undefined) {
resultDiv.innerHTML = "Error: Moles or Molarity missing for Volume calculation.";
return;
}
if (molarity === 0) {
resultDiv.innerHTML = "Molarity cannot be zero for Volume calculation.";
return;
}
volumeLiters = moles / molarity;
resultDiv.innerHTML = "Calculated Volume of Solution:
" + volumeLiters.toFixed(4) + " L";
} else { // All fields filled, assume user wants to calculate Molarity from Moles and Volume
if (volumeLiters === 0) {
resultDiv.innerHTML = "Volume cannot be zero.";
return;
}
molarity = moles / volumeLiters;
resultDiv.innerHTML = "Based on the provided Moles and Volume, the Molarity is:
" + molarity.toFixed(4) + " M (mol/L)";
}
}
function clearMolarityForm() {
document.getElementById('moles').value = ";
document.getElementById('volume').value = ";
document.getElementById('molarity').value = ";
document.getElementById('volumeUnit').value = 'mL';
document.getElementById('molarityResult').innerHTML = ";
}
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margin-bottom: 20px;
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text-align: center;
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}
What is Molarity?
Molarity (M), also known as molar concentration, is a measure of the concentration of a solute in a solution. It is defined as the number of moles of solute per liter of solution. Molarity is a fundamental concept in chemistry, particularly in quantitative analysis, solution preparation, and stoichiometry.
The Molarity Formula
The basic formula for molarity is:
M = n / V
- M: Molarity (mol/L or M)
- n: Moles of Solute (mol)
- V: Volume of Solution (L)
This formula can be rearranged to solve for any of the variables:
- To find Moles (n):
n = M * V
- To find Volume (V):
V = n / M
Units in Molarity Calculations
- Moles (mol): The SI unit for the amount of substance.
- Volume (L): The volume of the entire solution, not just the solvent. It must be in liters for the standard molarity calculation. Our calculator allows input in milliliters (mL) and automatically converts it to liters.
- Molarity (M or mol/L): Expressed as moles per liter.
How to Use the Molarity Calculator
- Identify Known Values: Determine which two of the three variables (Moles, Volume, Molarity) you already know.
- Enter Values: Input the known values into their respective fields. For volume, select the correct unit (mL or L).
- Leave Unknown Blank: Leave the field for the value you want to calculate empty.
- Click "Calculate": The calculator will then display the unknown value with the appropriate units.
- Clear: Use the "Clear" button to reset all fields for a new calculation.
Examples
Example 1: Calculating Molarity
You dissolve 0.25 moles of sodium chloride (NaCl) in enough water to make a 500 mL solution. What is the molarity of the solution?
- Moles of Solute: 0.25 mol
- Volume of Solution: 500 mL (which is 0.5 L)
- Molarity: (Leave blank)
Using the calculator, input 0.25 for Moles and 500 for Volume (with mL selected). The result will be 0.5000 M.
Calculation: M = 0.25 mol / 0.5 L = 0.5 M
Example 2: Calculating Moles of Solute
How many moles of glucose are present in 2.0 liters of a 0.15 M glucose solution?
- Moles of Solute: (Leave blank)
- Volume of Solution: 2.0 L
- Molarity: 0.15 M
Using the calculator, input 2.0 for Volume (with L selected) and 0.15 for Molarity. The result will be 0.3000 mol.
Calculation: n = 0.15 M * 2.0 L = 0.3 mol
Example 3: Calculating Volume of Solution
What volume (in mL) of a 0.8 M sulfuric acid (H₂SO₄) solution contains 0.4 moles of H₂SO₄?
- Moles of Solute: 0.4 mol
- Volume of Solution: (Leave blank)
- Molarity: 0.8 M
Using the calculator, input 0.4 for Moles and 0.8 for Molarity. The result will be 0.5000 L (or 500 mL if you convert).
Calculation: V = 0.4 mol / 0.8 M = 0.5 L
Why is Molarity Important?
Molarity is crucial in many chemical applications:
- Solution Preparation: It allows chemists to accurately prepare solutions of desired concentrations for experiments.
- Stoichiometry: Molarity is used to relate the amount of reactants and products in chemical reactions, especially in solution.
- Titrations: In acid-base titrations and other volumetric analyses, molarity is essential for determining unknown concentrations.
- Reaction Rates: The concentration of reactants (often expressed in molarity) directly influences the rate of a chemical reaction.