Understanding Normality
* Normality (N) is a measure of concentration that expresses the number of gram equivalents of a solute per liter of solution.
* Gram Equivalent is the mass of a substance that will react with or replace one mole of hydrogen ions (H+) in an acid-base reaction.
* For NaCl: The gram equivalent weight is equal to the molecular weight because each NaCl molecule provides one mole of chloride ions (Cl-) that can react with one mole of H+ ions.
Steps to Prepare a 0.2 N NaCl Solution
1. Determine the Molecular Weight of NaCl: The molecular weight of NaCl is 58.44 g/mol.
2. Calculate the Mass of NaCl Needed:
* Since the gram equivalent weight of NaCl is equal to its molecular weight, 0.2 N NaCl solution contains 0.2 gram equivalents of NaCl per liter.
* To make 1 liter of 0.2 N NaCl solution, you'll need:
* 0.2 gram equivalents/liter * 58.44 g/equivalent = 11.688 g of NaCl
3. Dissolve NaCl in Water:
* Weigh out 11.688 g of NaCl.
* Add it to a volumetric flask with a capacity slightly larger than 1 liter (e.g., a 1.2 L flask).
* Add a small amount of distilled water (about half the flask volume) and stir gently until the NaCl dissolves completely.
* Carefully add more distilled water until the solution reaches the 1-liter mark on the flask.
* Stopper the flask and invert it several times to ensure thorough mixing.
Important Considerations:
* Water Quality: Use distilled or deionized water to avoid introducing impurities.
* Accuracy: Use a balance with good accuracy to weigh the NaCl.
* Volumetric Flask: Use a volumetric flask for accurate volume measurement.
* Labeling: Label your solution clearly with the concentration (0.2 N NaCl), date of preparation, and any other relevant information.
Example: Preparing 500 mL of 0.2 N NaCl
* You would need half the amount of NaCl for a 500 mL solution (11.688 g / 2 = 5.844 g).
* Follow the same dissolution steps, but use a 500 mL volumetric flask.
