Physical Address
304 North Cardinal St.
Dorchester Center, MA 02124
D5562-95 – Standard Test Method Technical Guide
📐 Scope and Significance
ASTM D5562-95 (Reapproved 2018) is a standardized test method specifically designed for determining the acidity—measured as free fatty acids or acid number—in sulfonated or sulfated oils containing ammonium or triethanolamine soaps. The acidity value is derived indirectly through a calculation based on the total alkalinity and the free-and-alkali combined fatty acids in the sample.
This method is crucial for quality assurance in the leather industry, as it ensures the accurate assessment of fat and oil composition. All values stated in the standard are regarded as standard SI units.
🧪 Apparatus and Reagent Specifications
The precision of D5562 relies on a highly specific apparatus setup and the use of accurately standardized chemical reagents. A 300 mL borosilicate Erlenmeyer flask with a glass stopper is connected via a ground joint to a glass air condenser measuring 915 mm in length and 8 mm in outside diameter. Perforated glass beads (approx. 4 mm in diameter) are used to prevent bumping and must be pre-boiled until neutral to methyl orange.
The following tables detail the key apparatus dimensions and the standard reagent solutions required for the analysis. The strength of reagents is deliberately expressed in KOH equivalents to facilitate direct acid number calculation.
| 🟦 Component | 📏 Dimensions | 🎯 Requirement |
|---|---|---|
| Erlenmeyer Flask | 300 mL capacity | Borosilicate glass with glass stopper |
| Air Condenser | 915 mm (36 in.) length, 8 mm (5⁄16 in.) OD | Flared and ground lower end for ground joint |
| Perforated Glass Beads | Approx. 4 mm (5⁄32 in.) diameter | Chemically resistant glass, boiled to neutral |
| 🧪 Reagent | ⚡ Normality | 📐 KOH Equivalent |
|---|---|---|
| Sodium Hydroxide (NaOH) | 1 N | 56.1 mg KOH / mL |
| Sodium Hydroxide (NaOH) | 0.5 N | 28.05 mg KOH / mL |
| Sulfuric Acid (H₂SO₄) | 0.5 N | 28.05 mg KOH / mL |
⚙️ Determination Principle and Measured Properties
The acidity is determined by calculation from the total alkalinity and combined fatty acids. The method requires a Methyl Orange Indicator Solution (1 g/L), prepared by dissolving 0.1 g of methyl orange in 100 mL of water, and a Sulfuric Acid solution (1 + 19), made by carefully mixing 1 volume of concentrated H₂SO₄ (sp gr 1.84) into 19 volumes of water. The key measured property, the Acid Number, is calculated from the consumed titrant volumes and their KOH equivalents.
💡 Technician Tip: When preparing the Sulfuric Acid (1+19) solution, always carefully add the concentrated acid (sp gr 1.84) to the water while stirring to avoid violent exothermic reactions and ensure the solution is uniform.
⚠️ Safety Note: Perforated glass beads are mandatory to prevent bumping during the reflux process. Ensure beads are thoroughly cleaned and boiled until neutral to a methyl orange indicator before first use to prevent sample contamination and inaccurate results.
❓ Frequently Asked Questions
🔍 What materials are best suited for this test method?
This test method is specifically intended for sulfonated or sulfated oils in the presence of ammonium or triethanolamine soaps, primarily for quality assurance in leather processing.
💡 How is the strength of the standard NaOH solution expressed?
The concentration must be expressed as mg of KOH per mL. For example, 1 mL of 1 N NaOH is equivalent to 56.1 mg of KOH, while 1 mL of 0.5 N NaOH is equivalent to 28.05 mg of KOH.
📌 What are the exact dimensions of the air condenser?
The air condenser must be a glass tube measuring 915 mm (36 inches) in length with an outside diameter of 8 mm (5/16 in.). It must form a sealed ground joint connection with the flask.
⚡ Which standardized acid is specified as a reagent?
Sulfuric Acid (0.5 N) is the specified standard acid