To find the experimental molarity, you need to determine the number of moles of solute present in a known volume of solution. The fundamental formula is:
Molarity (M) = Moles of solute (n) / Volume of solution in liters (V)
Here's a step-by-step breakdown of how to do it:
Steps to Determine Experimental Molarity
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Determine the Mass of the Solute Used: Accurately weigh the solute used in the experiment.
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Convert Mass to Moles: Convert the mass of the solute to moles using its molar mass (grams per mole). You can calculate moles using the formula:
Moles (n) = Mass (g) / Molar Mass (g/mol)
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Measure the Volume of the Solution: Accurately measure the total volume of the solution in liters (L). Be sure to use appropriate glassware, like a volumetric flask, for accurate measurements. If the volume is measured in milliliters (mL), convert it to liters by dividing by 1000:
Volume (L) = Volume (mL) / 1000
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Calculate Molarity: Divide the number of moles of solute by the volume of the solution in liters.
Molarity (M) = Moles of solute (n) / Volume of solution in liters (V)
Example
Let's say you dissolve 4.0 grams of sodium chloride (NaCl) in enough water to make 500 mL of solution.
- Mass of Solute: 4.0 g NaCl
- Moles of Solute: The molar mass of NaCl is approximately 58.44 g/mol.
- n = 4.0 g / 58.44 g/mol = 0.0685 mol
- Volume of Solution: 500 mL = 0.5 L
- Molarity:
- M = 0.0685 mol / 0.5 L = 0.137 M
Therefore, the molarity of the NaCl solution is 0.137 M.
Important Considerations
- Accuracy: Use accurate weighing and volumetric techniques to minimize experimental error.
- Complete Dissolution: Ensure the solute is completely dissolved in the solvent before taking the volume measurement.
- Temperature: Molarity can be slightly affected by temperature due to changes in volume. If high precision is needed, record the temperature.
