Preparation and Standardization of 0.05N & 0.1N Potassium Thiocyanate (KSCN) Solutions

1. Materials Required

• Potassium thiocyanate (KSCN) – AR grade
• Standardized 0.05N or 0.1N AgNO₃ solution
• Ferric ammonium sulfate indicator (FeNH₄(SO₄₂·12H₂O)
• 6N Nitric acid (HNO₃)
• Distilled water
• Glassware: Burette, pipette, conical flask, volumetric flask (1L)

2. Preparation of Solutions

Solution	Molecular Weight (KSCN)	Weight Required (for 1L)
0.05N KSCN	97.18 g/mol	4.859 g
0.1N KSCN	97.18 g/mol	9.718 g

Procedure:

1. Weigh the calculated amount of KSCN accurately.
2. Dissolve in about 500mL distilled water in a 1L volumetric flask.
3. Dilute to the mark with distilled water and mix thoroughly.
4. Label as “Approx. 0.05N KSCN” or “Approx. 0.1N KSCN”.

3. Standardization (Volhard’s Method)

Procedure:

1. Pipette 25mL of standardized AgNO₃ solution into a conical flask.
2. Add 5mL of 6N HNO₃ to acidify the solution.
3. Add 1mL of ferric ammonium sulfate indicator.
4. Titrate with KSCN solution until a faint reddish-brown color persists for 30 seconds.
5. Record the volume of KSCN used (V₁).
6. Repeat in triplicate for accuracy.

Calculation:

N_KSCN = (N_AgNO3 × V_AgNO3) / V_KSCN

Example for 0.05N KSCN:

If 24.8mL KSCN was used to titrate 25mL of 0.05N AgNO₃:

N_KSCN = (0.05 × 25) / 24.8 = 0.0504N

Example for 0.1N KSCN:

If 24.5mL KSCN was used to titrate 25mL of 0.1N AgNO₃:

N_KSCN = (0.1 × 25) / 24.5 = 0.1020N

4. Precautions

• Use HNO₃ for acidification (avoid HCl or H₂SO₄)
• Standardize in triplicate (±1% variation acceptable)
• Store in amber glass bottles (light-sensitive)
• Re-standardize periodically

5. Applications

• Volhard’s method for halide determination
• Argentometric titrations
• Complexometric titrations involving silver