How Do You Calculate Molarity

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Molarity Calculator

Calculate the molar concentration of a solution

Milliliters (mL) Liters (L)

Result:

How Do You Calculate Molarity?

Molarity (M) is the most common way to express the concentration of a solution in chemistry. It represents the number of moles of a solute dissolved in exactly one liter (1 L) of solution.

The Molarity Formula

To calculate molarity, you need to know the amount of solute in moles and the total volume of the solution in liters. The fundamental formula is:

Molarity (M) = Moles of Solute (n) / Volume of Solution in Liters (V)

Step-by-Step Calculation Guide

  1. Find the Mass: Weigh the solute you are adding to the solution (in grams).
  2. Determine Molar Mass: Look up the atomic weights of the elements in your chemical formula on the periodic table to find the molar mass (g/mol).
  3. Calculate Moles: Divide the mass of the solute by its molar mass (Moles = Mass / Molar Mass).
  4. Measure Volume: Determine the final volume of the solution. Ensure you convert this to Liters (if you have mL, divide by 1000).
  5. Divide: Divide the number of moles by the volume in liters to get the Molarity.

Practical Example

Suppose you dissolve 5.84 grams of Table Salt (NaCl) into enough water to make 500 mL of solution.

  • Mass: 5.84 g
  • Molar Mass of NaCl: ~58.44 g/mol
  • Moles: 5.84 / 58.44 = 0.1 moles
  • Volume: 500 mL = 0.5 Liters
  • Molarity: 0.1 moles / 0.5 L = 0.2 M
function calculateMolarity() { var mass = parseFloat(document.getElementById('soluteMass').value); var molarMass = parseFloat(document.getElementById('molarMass').value); var volume = parseFloat(document.getElementById('solutionVolume').value); var unit = document.getElementById('volumeUnit').value; var resultWrapper = document.getElementById('resultWrapper'); var output = document.getElementById('molarityOutput'); var steps = document.getElementById('calculationSteps'); if (isNaN(mass) || isNaN(molarMass) || isNaN(volume) || mass <= 0 || molarMass <= 0 || volume <= 0) { alert("Please enter valid positive numbers for all fields."); return; } // Convert volume to Liters if necessary var volumeInLiters = unit === 'mL' ? volume / 1000 : volume; // Calculate Moles var moles = mass / molarMass; // Calculate Molarity var molarity = moles / volumeInLiters; // Display Result resultWrapper.style.display = 'block'; output.innerHTML = molarity.toFixed(4) + " mol/L (M)"; steps.innerHTML = "Calculation Breakdown:" + "1. Moles of Solute = " + mass + "g / " + molarMass + "g/mol = " + moles.toFixed(4) + " moles" + "2. Volume in Liters = " + volumeInLiters + " L" + "3. Molarity = " + moles.toFixed(4) + " moles / " + volumeInLiters + " L = " + molarity.toFixed(4) + " M"; // Smooth scroll to result resultWrapper.scrollIntoView({ behavior: 'smooth', block: 'nearest' }); }

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