Understanding Normality
* Normality (N) is a measure of concentration that refers to the number of gram equivalents of a solute dissolved per liter of solution.
* Gram Equivalent Weight (GEW) is the molecular weight of a substance divided by the number of equivalents it produces in a reaction.
Steps to Determine Normality
1. Write the Balanced Chemical Equation: This is crucial to determine the number of equivalents the ferrous ammonium sulfate will produce in a specific reaction. For example, let's assume you're using it as a reducing agent in a redox reaction where Fe²⁺ is oxidized to Fe³⁺:
Fe²⁺ + e⁻ → Fe³⁺
2. Calculate the Molecular Weight (MW) of Ferrous Ammonium Sulfate (FeSO₄(NH₄)₂SO₄·6H₂O):
* Fe: 55.845 g/mol
* S: 32.065 g/mol
* O: 15.999 g/mol
* N: 14.007 g/mol
* H: 1.008 g/mol
* MW = (55.845 + 32.065 + 15.999*4 + 14.007*2 + 1.008*8 + 15.999*6) = 392.14 g/mol
3. Determine the Number of Equivalents: In the reaction above, one mole of ferrous ammonium sulfate (FeSO₄(NH₄)₂SO₄·6H₂O) produces one mole of Fe²⁺, which releases one electron (e⁻). Therefore, one mole of ferrous ammonium sulfate is equivalent to one equivalent.
4. Calculate the Gram Equivalent Weight (GEW):
* GEW = MW / Number of Equivalents = 392.14 g/mol / 1 = 392.14 g/equivalent
5. Determine the Mass of Ferrous Ammonium Sulfate: Weigh out the exact mass of ferrous ammonium sulfate you are using for your solution.
6. Calculate the Normality:
* Normality (N) = (Mass of Solute (g) / GEW (g/equivalent)) / Volume of Solution (L)
Example:
* You dissolve 10.0 g of ferrous ammonium sulfate in 250 mL of water.
* Step 1: You have the balanced equation from earlier.
* Step 2: You calculated the MW to be 392.14 g/mol.
* Step 3: You know one mole produces one equivalent.
* Step 4: You calculated the GEW to be 392.14 g/equivalent.
* Step 5: You have 10.0 g of ferrous ammonium sulfate.
* Step 6:
* N = (10.0 g / 392.14 g/equivalent) / (0.250 L)
* N ≈ 0.102 N
Important Notes:
* Hydrated Salt: Be sure to use the molecular weight of the hydrated form of ferrous ammonium sulfate (FeSO₄(NH₄)₂SO₄·6H₂O) if you are using the hydrated salt.
* Reaction-Specific: Normality is reaction-specific. The number of equivalents will vary depending on the reaction where the ferrous ammonium sulfate is used.
* Purity: If your ferrous ammonium sulfate is not 100% pure, you will need to adjust your calculations accordingly.
