Agricultural grade is the lowest-purity commercial designation of ammonium chloride, and the designation describes a purity floor rather than a physical form — material sold under it may be crystalline, powdered or compacted. The grade exists because a fertilizer buyer is purchasing nitrogen and chloride, not chemical purity, so residual sodium chloride and trace insolubles carried over from manufacture are tolerated at levels that would disqualify the same material from technical or feed use. This page defines the grade; the form-specific pages in this family describe how it is physically supplied.
Substance identity
| Chemical name | Ammonium chloride |
| Synonyms | Sal ammoniac, salmiac, muriate of ammonia, ammonium muriate |
| Formula | NH₄Cl |
| CAS | 12125-02-9 |
| PubChem CID | 25517 |
| Molar mass | 53.49 g/mol |
| Appearance | White to off-white crystalline solid; agricultural material is frequently slightly off-white or faintly grey rather than optically white, which reflects residual impurity and is not by itself a defect |
Specification
| Parameter | Value | Basis |
|---|---|---|
| NH₄Cl content | ≥ 94–96 % | Typical commercial range |
| Nitrogen (N) | ≥ 25.0–25.4 % | Typical commercial range |
| Nitrogen, theoretical maximum | 26.2 % | Calculated from formula |
| Chloride, theoretical | 66.3 % | Calculated from formula |
| Moisture (H₂O) | ≤ 0.5–1.0 % | Typical commercial range |
| Principal residual impurity | Sodium chloride | Characteristic of soda-ash co-product material; ceiling to be fixed in the specification |
| Colour | White to off-white | — |
A stated N figure and a stated NH₄Cl figure are not independent: at 26.2 % N for the pure salt, 96 % NH₄Cl corresponds to approximately 25.1 % N. A specification quoting both should be internally consistent, and an N figure above 26.2 % is not physically possible for this compound.
Properties
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Solubility. Freely soluble in water: approximately 29 g per 100 g water at 0 °C, 37 g at 20 °C and 77 g at 100 °C. Solubility rises steeply with temperature, which is why the salt is readily recrystallised. Sparingly soluble in ethanol; essentially insoluble in acetone and diethyl ether.
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Dissolution enthalpy. Dissolution is endothermic, about +14.8 kJ/mol, so concentrated solutions cool noticeably as they are made up.
- Hygroscopicity. Only moderately hygroscopic. The critical relative humidity is commonly cited at roughly 77 % at 30 °C — high enough that the salt is stable in ordinary dry storage, low enough that it will pick up water in a humid, unventilated warehouse.
- Thermal behaviour. Does not melt under ordinary conditions. On heating it dissociates into ammonia and hydrogen chloride, which recombine on cooling, giving the appearance of sublimation at about 337.6 °C. Loss becomes measurable well below that temperature.
- Solution pH. Aqueous solutions are acidic, typically pH 4.5–6.0 for a 5 % solution at 25 °C. This follows from the salt being formed from a strong acid and a weak base: the conjugate acid NH₄⁺ has a pKa of 9.25, so it hydrolyses appreciably in water.
- Density. True crystal density approximately 1.53 g/cm³.
Applications
Straight nitrogen fertilizer, and a nitrogen source for compound NPK manufacture. Its distinguishing agronomic characteristic is that the counter-ion is chloride rather than sulfate or nitrate. This matters in two situations. In flooded rice, sulfate-based ammonium sources introduce sulfate that can be reduced microbially to sulfide under anaerobic conditions and injure roots; a chloride-based source avoids that pathway. In chloride-tolerant crops generally — rice, coconut, oil palm, cotton and other fibre crops, and many cereals — the chloride is not merely inert ballast, since chloride is an essential plant micronutrient with roles in the oxygen-evolving complex of photosystem II, in stomatal regulation and in osmoregulation.
Handling and storage
Store dry, sealed and off the floor, ideally in moisture-barrier-lined packaging. Caking is driven less by average humidity than by temperature cycling: the salt dissolves at inter-particle contact points during humid warm periods and recrystallises as solid bridges when conditions dry, so a warehouse with a large day–night swing cakes material that a stable warm warehouse would not. Do not co-store or blend with alkaline materials — lime, cement, basic slag, calcium cyanamide — because they liberate ammonia and destroy the nitrogen value. In the presence of moisture the material is aggressive towards copper and its alloys, mild steel, galvanised steel and aluminium; chloride also raises the pitting risk on austenitic stainless steels. Prefer plastic, GRP or lined equipment.
Notes
Nitrification of ammonium releases two hydrogen ions per nitrogen atom, so all ammonium fertilizers acidify soil. Because ammonium chloride carries more nitrogen per tonne than ammonium sulfate, its acidifying effect per tonne applied is correspondingly greater. On low-buffer or already acid soils, plan liming alongside its use. Grade designations for ammonium chloride are set by different national standards, which are not interchangeable; the applicable standard should be named explicitly in the specification rather than assumed.