.jpg?w=218&resize=218,150&ssl=1 "UNESCO Zollverein Coal Mine Industrial Complex & Other Things to do in Essen, Germany | My Travelogue")
🧪 Testing Process for Liquid Ammonia Concentration
The complete testing process generally involves two key parts: a physical measurement (Density/Specific Gravity using a Hydrometer) and a chemical measurement (Concentration/Assay using Titration).
1. Hydrometer Measurement (Density)
This step measures the physical property of the liquid ammonia solution, which is often correlated to its concentration using standardized tables.
- Sample Preparation: Take a sufficient quantity (e.g., 500 mL or as needed for the hydrometer jar) of the liquid ammonia sample, ensuring the sample is representative and contained to prevent loss of volatile ammonia (as noted in the image, “take sample ≈500 mL overflow”).
- Procedure:
- Carefully pour the sample into a graduated cylinder or a hydrometer jar.
- Gently immerse a calibrated Hydrometer into the sample, ensuring it floats freely and does not touch the sides or bottom.
- Record the reading on the hydrometer scale, which gives the Specific Gravity or Density (e.g., d25,25 as mentioned in general methods).
- Record the temperature of the sample at the time of reading.
- Purpose: The density (D) is a critical parameter, as seen in your calculation formula, and is used to convert volume measurements to mass/weight for accurate concentration calculation.
2. Acid-Base Titration (Assay)
This is a direct titration of the weak base, ammonia (NH3), with a strong acid, Hydrochloric Acid (HCl), to determine its concentration.
The reaction is: NH3(aq)+HCl(aq)→NH4Cl(aq)
Procedure based on your notes:
- Sample Preparation:
- Accurately measure and transfer a small, specified volume of the sample (e.g., 0.5 mL) into a conical flask or beaker.
- Dilute the sample with a known volume of water (e.g., 25 mL of water).
- Indicator and Titration Setup:
- Add a few drops (e.g., 1 drop) of Phenolphthalein indicator solution to the sample in the flask. Note: Phenolphthalein’s end-point (pH 8.3-10.0) is typically used for titrating a strong base with a weak acid, or in a back-titration. For a weak base (NH3) with a strong acid (HCl), an indicator like Methyl Red or Methyl Orange is generally preferred because the equivalence point is acidic (around pH 5-6). Your note’s use of Phenolphthalein suggests a specific context, perhaps a titration to a pre-defined basic endpoint or a titration using a specific neutralized formaldehyde method, but for a direct titration, Methyl Red is standard.
- Ensure the titrant, 0.1 N HCl (standardized Hydrochloric Acid), is loaded into the burette and the initial volume is recorded.
- Titration:
- Titrate the diluted ammonia solution in the flask with the 0.1 N HCl from the burette.
- Swirl the flask constantly.
- The end-point is reached when the solution color changes from its initial color to colorless (the expected change for Phenolphthalein going from basic to acidic). If Methyl Red were used, the change would be from yellow to red.
- Reading:
- Record the final burette reading. The volume of HCl consumed (T.R. or Titre Reading) is the difference between the final and initial readings.
3. Calculation of Concentration
The concentration of ammonia (expressed as a percentage by weight, %w/w) is calculated using the titration volume and the density reading.
Your notebook provides a specific formula:
% w/w=DensityT.R.×0.01703×N(HCl)×100
Where:
- T.R. is the Titre Reading (mL of HCl consumed).
- 0.01703 is likely the Equivalent Weight of NH3 in grams (Molar Mass of NH3 is ≈17.03 g/mol). The value 0.01703 is 100017.03, representing the mass of NH3 in grams equivalent to 1 mL of 1 N acid.
- N(HCl) is the Normality of the HCl solution (e.g., 0.1 N or a precise standardized value).
- Density is the density of the liquid ammonia sample (often ≈0.9 for concentrated ammonia, though it should be the value measured by the hydrometer in Step 1).
- The ×100 converts the final mass fraction to a percentage.
Maximum Limit (N.L.T.)
The final line of your note, “N.L.T. 23.07”, likely stands for “Not Less Than 23.07 percent,” indicating a minimum purity specification for the liquid ammonia being tested.
This video provides an introduction to the general principles of acid-base titrations, which is the foundational chemical method used in your analytical notes.
