Understanding Normality
* Normality (N) is a measure of concentration that refers to the number of gram equivalents of a solute per liter of solution.
* Gram Equivalent Weight (GEW) is the molecular weight of a compound divided by the number of replaceable hydrogen ions (for acids) or hydroxide ions (for bases), or the number of electrons transferred in a redox reaction.
Potassium Dichromate (K₂Cr₂O₇) in Redox Reactions
In redox reactions, potassium dichromate acts as an oxidizing agent. The chromium (Cr) in dichromate ions (Cr₂O₇²⁻) has an oxidation state of +6. It can gain electrons and be reduced to Cr³⁺. The number of electrons transferred per dichromate ion is 6.
Calculations
1. Molecular Weight of K₂Cr₂O₇: 294.18 g/mol
2. Gram Equivalent Weight (GEW): 294.18 g/mol / 6 = 49.03 g/mol
3. Mass Needed for 1 N Solution: Since 1 N means 1 gram equivalent per liter, you need 49.03 g of K₂Cr₂O₇ to make 1 L of a 1 N solution.
Procedure
1. Weigh: Carefully weigh out 49.03 g of potassium dichromate using an analytical balance.
2. Dissolve: Add the weighed potassium dichromate to a 1 L volumetric flask.
3. Add Water: Slowly add distilled or deionized water to the flask, swirling gently to dissolve the potassium dichromate. Do not fill the flask to the 1 L mark yet.
4. Adjust Volume: Once the potassium dichromate is completely dissolved, add more water until the solution reaches the 1 L mark on the volumetric flask. Stopper the flask and mix well.
5. Label: Label the solution clearly as "1 N Potassium Dichromate."
Safety Precautions
* Potassium dichromate is a powerful oxidizing agent and is toxic. Wear appropriate personal protective equipment (PPE), including gloves, goggles, and a lab coat, while handling it.
* Work in a well-ventilated area.
* Avoid contact with skin and eyes.
* Dispose of the solution properly.
Note: This procedure is for guidance only. Please consult relevant safety data sheets (SDS) and laboratory guidelines for specific safety procedures and disposal protocols.
