Ammonium Hydroxide 29%: The Complete Guide to NH₄OH Uses, Grades & Safety
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📋 What You'll Learn
This guide walks you through ammonium hydroxide 29%: the complete guide to nh₄oh uses, grades & safety with detailed instructions.
The same molecule that cleans semiconductor wafers in a $14 billion fab also lives in your glass cleaner. A field guide to NH4OH at industrial concentration: chemistry, six commercial uses, grade selection, and how to buy it without setting your shipping department on fire.
Ammonium hydroxide (NH4OH) is one of the most quietly important industrial chemicals in modern manufacturing. It cleans the silicon wafers in every smartphone you’ve ever owned. It darkens the cocoa in Dutch-process chocolate. It stabilizes natural rubber latex on its way from a Malaysian plantation to a hospital glove plant. It runs the buffer chemistry in thousands of analytical labs. And, in dilute form, it’s the active ingredient in your bottle of glass cleaner.
At 29%, ammonium hydroxide is the standard industrial concentration — strong enough to be useful in a single dose, dilute enough to handle (with proper PPE) without specialized cryogenic equipment. We supply 29% in both ACS Reagent Grade and Technical Grade, in pack sizes from 1-quart bottles to 275-gallon IBC totes. We field these specification questions every week from semiconductor procurement engineers, food formulators, contract cleaning manufacturers, and lab managers — so this guide bundles the answers in one place: what NH4OH is, what it actually does, which grade you need, and how to specify it on a purchase order.
What is ammonium hydroxide? The chemistry under the label
Ammonium hydroxide is, strictly speaking, a misnomer. There is no stable molecule with the formula NH4OH that you can isolate in a bottle. What’s actually in the bottle is an aqueous solution of ammonia gas (NH3) dissolved in water (H2O), with the two species existing in dynamic equilibrium:
NH3 + H2O ⇌ NH4+ + OH−
The equilibrium sits far to the left. At room temperature, only about 1 in 200 dissolved ammonia molecules has actually grabbed a proton from water to form the ammonium cation NH4+ and a hydroxide anion OH−. The rest stays as free NH3. So when a label reads "29% ammonium hydroxide," what’s really in the bottle is approximately 29% by weight ammonia in water — with a tiny fraction of that ammonia ionized at any given instant.
This single fact — that it’s mostly free ammonia, not ionized hydroxide — explains nearly every property of NH4OH that surprises new users:
- It smells. The free NH3 has an extremely high vapor pressure (about 760 torr for pure ammonia at 25°C), so even a sealed bottle leaks ammonia gas through caps and gaskets.
- It loses strength over time. Open the bottle and ammonia escapes preferentially — the solution gets weaker every time you use it. A 29% bottle stored with a poor seal can drop to 26% in months.
- It freezes the wrong way. Concentrated solutions don’t freeze sharply; they slush. The 29% strength has a freezing point near −57°C, well below typical winter shipping conditions.
- It plays havoc with copper and brass. Free ammonia forms intensely colored, soluble copper-amine complexes — which is why you never store ammonium hydroxide in copper-fitted plumbing.
Key physical properties (29% solution at 25°C)
| Property | Value | Notes |
|---|---|---|
| Specific gravity | ~0.897 at 25°C | Less dense than water; the more concentrated, the lighter the solution |
| pH | ~11.6 | Strongly alkaline, but not as high as 29% NaOH (~14) |
| pKb (of NH3) | 4.75 | Weak base — see next section |
| Boiling point | ~37.7°C (99.9°F) | NH3 escapes long before water boils |
| Freezing point | ~−57°C (−70°F) | Doesn’t freeze in transit during winter |
| Vapor pressure | ~480 mm Hg at 25°C | Very high — always vent, always ventilate |
| CAS Number | 1336-21-6 | Same regardless of concentration |
| Molecular weight | 35.05 g/mol | For NH4OH equivalent; NH3 alone is 17.03 g/mol |
The "ammonia" naming convention. Industry uses several interchangeable names: ammonium hydroxide, aqueous ammonia, ammonia water, household ammonia (for the dilute consumer form), and "stronger ammonia water" (the obsolete USP designation for ~28%). They all refer to the same NH3/H2O equilibrium system. Concentration tells you what you actually have.
Strong base or weak base? The 29% question
This question shows up constantly in chemistry classes and on procurement specs, and the answer is genuinely a little subtle. Ammonium hydroxide is a weak base by classical Brønsted-Lowry definition — but at 29% concentration, it has plenty of OH− kinetics to act like a strong base in many practical applications.
"Strong" and "weak" in acid-base chemistry refer specifically to the fraction of the dissolved species that ionizes. Sodium hydroxide is a strong base because essentially 100% of dissolved NaOH dissociates into Na+ and OH− in water. Ammonia is a weak base because, as we saw above, only about 0.5% of dissolved NH3 picks up a proton at any instant. The pKb of 4.75 quantifies that weakness.
So why does 29% NH4OH still feel "strong" in the lab?
- Concentration overcomes weakness. Even a small ionization fraction times a large total concentration produces meaningful OH−. A 29% solution has roughly 16 molar total ammonia. The 0.5% ionized fraction still gives ~0.08 M OH− — enough to drive the pH to 11.6.
- The Le Chatelier reservoir. When you consume OH− in a reaction, the equilibrium shifts right and replaces it. The 29% solution holds an enormous reservoir of free NH3 waiting to ionize on demand. So while sodium hydroxide gives you all its base up front, ammonium hydroxide releases it kinetically as you use it — a different shape, but plenty of total capacity.
- Buffering at the bench. The same equilibrium that makes ammonia weak makes ammonium-ammonia mixtures excellent buffers around pH 9–10. This is why ammonia chemistry shows up in so many lab buffer recipes — it self-stabilizes against perturbation in a way strong bases cannot.
Procurement-spec rule of thumb. If a process spec calls for a strong, predictable, irreversible base (caustic etching, saponification), use sodium hydroxide. If the spec calls for a milder, volatile, residue-free base (cleaning, buffering, latex stabilization, tissue preparation), 29% NH4OH is usually the right pick — and it leaves no metal cation behind.
The 6 industries that run on 29% NH4OH
Outside of the cleaning aisle, ammonium hydroxide is mostly invisible to the public — but it’s a foundation chemical in six major commercial sectors. Each uses 29% as the standard incoming concentration; each dilutes or reacts it differently downstream.
Every silicon wafer in modern chip fabrication passes through an SC-1 bath — a 5:1:1 mixture of water, 29% hydrogen peroxide, and 29% ammonium hydroxide at 70–80°C. The peroxide oxidizes organic surface contaminants and the ammonia complexes trace metals (Cu, Ag, Ni, Cd, Co, Zn) into soluble amine complexes that rinse away. Without SC-1, no functioning chips. The semiconductor industry alone consumes hundreds of thousands of metric tons of NH4OH annually.
Dutch-process cocoa gets its darker color and milder flavor from alkalization with food-grade ammonium hydroxide (or potassium carbonate) — the higher pH neutralizes natural acidity in cacao. NH4OH also serves as a pH adjuster in baked goods, cheese aging, and pet food formulation. Use is regulated under 21 CFR 184.1139 with no upper limit when used per Good Manufacturing Practice.
Most commercial and household glass cleaners contain 1–3% ammonia — enough to dissolve oily residues, low enough that the volatile NH3 evaporates without streaking. Industrial degreasers, oven cleaners, and floor strippers run higher concentrations (5–10%). 29% is the bulk feedstock; formulators dilute and blend on demand.
Field-tapped natural rubber latex coagulates in hours without preservative. Adding 0.6–0.7% ammonia to the latex by weight raises the pH above 10 and prevents bacterial coagulation through the entire shipping and processing chain — from plantation to glove plant or tire factory. "High-ammonia latex" is the standard industrial designation; nearly every natural-rubber product passes through ammonia preservation.
Ammonia/ammonium-chloride buffers (pH 8–11) are workhorses in classical analytical labs — EDTA titrations, metal complexation, qualitative cation analysis, kjeldahl nitrogen determination. ACS Reagent Grade NH4OH is required because trace metal contamination in lower grades will throw off complexometric endpoints.
Aqua ammonia is one of the cheapest sources of plant-available nitrogen on a per-pound-of-N basis. Field application is typically through knife-injection rigs that bury the solution below 4 inches to prevent volatilization. This is the "agricultural ammonia" sometimes confused with anhydrous ammonia — the latter is dramatically more hazardous and entirely different chemistry.
The cleaning chemistry: why ammonia outperforms detergent on glass
If you’ve ever wondered why your $4 bottle of glass cleaner doesn’t leave streaks while your soapy water does, the answer is volatility. Soap and detergent solutions leave a thin surfactant film as the water evaporates; that film is what catches sunlight and shows streaks. Ammonia, by contrast, evaporates entirely — along with the water that carried it — leaving nothing behind on the glass. The cleaning happens; the residue doesn’t.
What ammonia actually does on a dirty surface
Three mechanisms work in parallel. The high pH (~11) saponifies skin oils and ester-based residues, converting them to water-soluble salts. The free ammonia molecules act as a mild solvent for nicotine, smoke residue, and other amine-soluble grime. And the fast-evaporating water/ammonia carrier means nothing pools on a vertical surface long enough to drip-dry into streaks.
Concentration math for the formulator
| End-use product | Working ammonia % | Dilution from 29% stock |
|---|---|---|
| Glass & window cleaner | 1–3% | 1 part 29% stock + 9–28 parts water |
| All-purpose surface spray | 2–5% | 1 part 29% + 5–14 parts water |
| Oven & range hood degreaser | 5–10% | 1 part 29% + 2–5 parts water |
| Floor stripper (heavy-build wax) | 10–15% | 1 part 29% + 1–2 parts water |
| Jewelry & silverware bath | 5–10% | 1 part 29% + 2–5 parts water |
NEVER mix ammonia with bleach. Sodium hypochlorite plus ammonia produces chloramine vapors (NH2Cl, NHCl2) which are acutely toxic and have killed cleaning workers in confined spaces. The combination shows up most often when an "ammonia" cleaner and a "bleach" cleaner are used in sequence in a poorly ventilated bathroom. Read every label before mixing, and never combine an ammonia-based cleaner with anything containing chlorine bleach — not in the same bucket, not on the same surface, not in the same hour without rinsing in between.
Concentration guide: 10%, 19%, 28%, 29% — and why we stock 29%
Ammonium hydroxide is sold across a wide range of concentrations, and the right pick depends almost entirely on whether you’re buying for end-use or as a feedstock. Higher concentration costs less per pound of available ammonia, ships in fewer drums, and gives you formulation flexibility — at the cost of stricter handling rules. Lower concentration is simpler to use directly but cost-inefficient at any meaningful volume.
The available concentration grades
| Concentration | Common name | Typical buyers | Notes |
|---|---|---|---|
| ~5–10% | Household ammonia, "clear ammonia" | Consumer / janitorial retail | Diluted ready-to-use; expensive per unit NH3 |
| ~19% | Reduced-strength industrial | Some food formulators, sensitive labs | Available but rarely cost-justified |
| ~28% | USP "Stronger Ammonia Water" | Pharmaceutical / USP-spec users | Older USP designation; functionally similar to 29% |
| 29% | Industrial / ACS Reagent | Semiconductor, food, cleaning, lab, agriculture | Standard industrial concentration |
| ~30% | "Concentrated" | Bulk users with refrigerated storage | Slightly higher vapor pressure; harder to ship |
Why 29% is the sweet spot
29% sits at a deliberate engineering optimum. It’s strong enough that you’re not paying to ship water, but dilute enough that it’s stable at typical warehouse temperatures (vapor pressure rises sharply above 30%). It’s the standard concentration on every major chemical distributor catalog and the assumed input for every published industrial procedure — RCA SC-1, USP cocoa alkalization, FDA-direct-food-additive specs, MIL-A-43447 latex preservation. If a procedure says "ammonium hydroxide" without specifying concentration, it almost always means 29%.
For most operations, the math is straightforward: buy 29%, dilute on demand to your working strength. A 5-gallon pail of 29% NH4OH yields ~50 gallons of 3% glass cleaner concentrate. The same 50 gallons bought as ready-to-use 3% costs roughly 4–5x more before freight is even calculated.
ACS Reagent vs Technical Grade: which do you actually need?
The 29% concentration tells you what fraction of the bottle is ammonia. The grade tells you how clean the rest is — specifically, what trace impurities are allowed and how rigorously they’re certified. We supply 29% in both ACS Reagent Grade and Technical Grade, and the right pick is rarely about purity sensitivity in the abstract; it’s about whether your downstream process is sensitive to trace metals.
| Spec | ACS Reagent Grade | Technical Grade |
|---|---|---|
| Assay (NH3 content) | 28.0–30.0% | 28–30% (typical) |
| Heavy metals (as Pb) | ≤ 1 ppm certified | Not specified / batch dependent |
| Iron | ≤ 0.2 ppm | Not certified |
| Chloride | ≤ 1 ppm | Not certified |
| Sulfate | ≤ 1 ppm | Not certified |
| Residue after evaporation | ≤ 0.002% | Not specified |
| COA on every batch | Yes — ACS-spec analytical results | Yes — assay + appearance only |
| Cost per gallon | $$$ — typically 30–60% premium | $$ — baseline industrial price |
When ACS Reagent is required
Use ACS Reagent Grade when trace metal contamination would interfere with the downstream chemistry: complexometric titrations, ion chromatography mobile phases, semiconductor wafer cleaning (trace Fe and Cu can deposit on wafer surfaces and ruin device performance), trace-metals analytical work, sensitive pharmaceutical synthesis, and any procedure where the published method specifies "ACS Reagent Grade" or "ASTM Type II" reagent. Spending the premium is cheap insurance against a contaminated batch wasting downstream work.
When Technical Grade is the right call
Use Technical Grade for industrial cleaning manufacture, agricultural ammonia injection, latex stabilization, large-volume neutralization (acid-stream pH adjustment in wastewater treatment), most food formulation (assuming you carry separate FCC documentation), and any process where the chemistry tolerates routine industrial-purity input. The Technical Grade COA still certifies assay — you know you’re getting 29% — it just doesn’t certify trace-metal limits. For a contract cleaner formulator making 10,000 gallons of glass cleaner, the trace-iron question is irrelevant; for an analytical chemist running EDTA titrations, it’s the entire ballgame.
FCC vs ACS for food use. ACS Reagent Grade is the analytical-purity standard. FCC (Food Chemicals Codex) is the food-additive purity standard. They’re different specifications, even though FCC limits are usually similar to ACS for the metals that matter. If you’re using NH4OH in food processing, ask for FCC-certified material specifically — ACS alone is not sufficient documentation for an FDA inspector.
Safety: TLV, PPE, storage, and the never-mix list
29% ammonium hydroxide is corrosive (DOT Class 8) and acutely toxic via inhalation. The hazard is dominated by the high vapor pressure of free NH3: just opening a container in still air will produce immediately detectable concentrations near the cap. Standard industrial controls work, but only if applied. Operations that "just go quick" without ventilation are how chronic exposures — and ER visits — happen.
Exposure limits
- OSHA PEL: 50 ppm 8-hr TWA
- NIOSH REL: 25 ppm 8-hr TWA, 35 ppm 15-min STEL
- ACGIH TLV: 25 ppm 8-hr TWA, 35 ppm 15-min STEL
- NIOSH IDLH: 300 ppm
- Detection threshold: ~5 ppm — you can smell it well below the OSHA limit, which is the warning sign that ventilation isn’t adequate
Required PPE for handling 29%
- Chemical splash goggles (full ventilation goggles — not safety glasses)
- Face shield over goggles when decanting or pouring
- Nitrile or butyl rubber gloves (avoid latex — ammonia degrades natural rubber)
- Long-sleeve chemical-resistant apron or coverall
- Closed-toe chemical-resistant footwear
- Local exhaust ventilation (fume hood for small-scale; LEV snorkels or full slot ventilation for production)
- Cartridge respirator (ammonia-rated, e.g., NIOSH "K"-cartridge) for backup; full-face SCBA for spill response
Storage rules
- Cool (under 70°F where possible), well-ventilated, away from direct sunlight
- Original sealed container preferred; if decanting, use HDPE or stainless steel — never copper, brass, zinc, aluminum, or galvanized steel
- Segregate from acids, oxidizers, halogens, and hypochlorites — OSHA storage compatibility class 4.2 (alkali)
- Keep containers vented or use pressure-relief caps — sealed bottles in a warm warehouse can develop measurable internal pressure
The never-mix list. Never combine 29% NH4OH with: sodium hypochlorite (chloramine gas), calcium hypochlorite, chlorine gas, hydrochloric acid (forms ammonium chloride aerosol), nitric acid (violent), iodine (forms shock-sensitive nitrogen triiodide), mercury salts, or strong oxidizers. When in doubt, neutralize incompatibles separately, then dispose, then move on.
Spill response and first aid
For small spills (under 1 gallon): evacuate the area, ventilate, and absorb with vermiculite or sand. Do not flush large volumes to drain without dilution — high-pH ammonia slugs damage biological wastewater treatment. For skin contact, flood with water for 15 minutes minimum and remove contaminated clothing. For eye contact, flush with eyewash for 15 minutes and seek medical evaluation immediately. For inhalation, evacuate to fresh air and seek medical evaluation if any respiratory irritation persists past a few minutes.
Buying smart: pack sizes, freight, and how we ship 29%
For most industrial buyers, the right pack size is determined by usage rate divided by shelf-life concerns. 29% NH4OH stored properly has a 2–3 year shelf life, but every time a container is opened, ammonia escapes preferentially — so smaller containers used quickly are often more cost-effective than a large drum used over a year. We supply the full range:
| Pack size | Typical buyer | Freight class |
|---|---|---|
| 1 quart | Lab use, sample testing, small-batch QC | Limited Quantity ground; often air-restricted |
| 1 gallon | Small lab, R&D, repackage formulation | Class 8 ground only |
| 5-gallon pail | Mid-volume cleaning manufacturer, small fab | Class 8 LTL freight |
| 55-gallon drum | Production cleaning manufacturer, lab supply, agricultural injection | Class 8 LTL or full-truckload |
| 275-gallon IBC tote | Bulk industrial — semiconductor fab, latex processor, food manufacturer | Class 8 LTL with reinforced pallet |
What to specify on a purchase order
To avoid back-and-forth on a procurement spec, include all five of these fields:
- Concentration: "29% NH4OH" (or 28–30% range if your spec accepts it)
- Grade: ACS Reagent or Technical (or FCC for food applications)
- Pack size: By volume and container type (quart bottle, gallon bottle, 5-gal pail, 55-gal drum, 275-gal tote)
- Documentation: COA on every shipment is standard. SDS is required for any hazmat order. TDS if your QA chain wants the full data sheet.
- Freight method: Ground LTL is standard. Some destinations require dock height or liftgate specifications — confirm in advance.
Lead time and shipping windows
Most pack sizes ship within 1–2 business days from our Texas warehouse. IBC totes and full-pallet drum quantities sometimes require 3–5 business days for crating and freight scheduling. Class 8 hazmat moves on ground LTL only — no air freight — so transit is dictated by carrier transit map, typically 2–5 business days continental US. We process orders during business hours with email confirmation; we don’t make same-day shipping promises that ground LTL networks can’t deliver on.
If you’re placing your first order: Request a sample-quart bottle for QA verification before committing to drum or tote quantity. We’ll send a 1-quart sample with full COA at the same lot you’d receive in production. This is the standard procurement workflow for new vendor onboarding in regulated industries — insist on it whenever you’re evaluating a chemical supplier.
Stock 29% ammonium hydroxide for your operation
ACS Reagent Grade and Technical Grade. Pack sizes from 1-quart bottles to 275-gallon IBC totes. Audit-ready COA, SDS, and TDS with every shipment.
Shop 29% ammonium hydroxideReferences & Authoritative Sources
Chemical identity, properties, and safety data sourced from the U.S. National Library of Medicine's PubChem database — the authoritative open-chemistry data resource maintained by the National Institutes of Health.
- PubChem CID 14923: Ammonium Hydroxide 29% ACS Grade — National Center for Biotechnology Information, U.S. National Library of Medicine. CAS 1336-21-6.
Frequently Asked Questions
Is ammonium hydroxide a strong base or a weak base?
It is a weak base by classical definition (pKₒ = 4.75) — only about 0.5% of dissolved ammonia ionizes to NH₄⁺ and OH⁻ at any instant. However, at 29% concentration the total reservoir of ammonia is so large that the solution behaves like a moderately strong base in practice, with a pH of about 11.6 and ample OH⁻ available to drive reactions. Use sodium hydroxide if you need a strong, irreversible base; use 29% NH₄OH if you need a milder, volatile base that leaves no metal cation behind.
What is the pH of 29% ammonium hydroxide?
About 11.6 at 25°C. This is strongly alkaline but lower than 29% sodium hydroxide (pH ~14) because ammonia only partially ionizes. The pH drops slowly as the solution loses ammonia to evaporation — a year-old open bottle may read 10.5 or below.
What is the boiling point of ammonium hydroxide?
Approximately 37.7°C (99.9°F) for the 29% solution. The ammonia component evaporates long before water boils — which is why ammonia is always handled cool and stored well below room temperature when possible. There is no clean "boiling point" for ammonium hydroxide because the ammonia leaves the solution gradually starting at room temperature.
Is ammonium hydroxide the same as ammonia?
Functionally yes, technically no. "Ammonium hydroxide" is the historical name for an aqueous solution of ammonia gas (NH₃) in water. Pure ammonia is the gas itself, NH₃. There is no isolable molecule with the formula NH₄OH — the name describes the ionization equilibrium that exists in solution, not a discrete compound. Industrial procurement uses both names interchangeably.
Can I mix ammonia with bleach?
No — never. Ammonia plus sodium hypochlorite produces chloramine vapors (NH₂Cl, NHCl₂) which are acutely toxic and have killed workers in confined cleaning spaces. Don’t use an ammonia-based cleaner immediately after a bleach cleaner without thorough rinsing. Don’t store the two in the same secondary container or spill kit. Treat them as fully incompatible.
What is the difference between ACS Reagent Grade and Technical Grade ammonium hydroxide?
Both grades supply ~29% NH₃ in water. ACS Reagent Grade is certified to meet American Chemical Society purity specifications — with documented limits on heavy metals (≤1 ppm), iron (≤0.2 ppm), chloride, sulfate, and residue after evaporation. Technical Grade meets the assay specification but does not certify trace metal limits. ACS is required for analytical chemistry, semiconductor cleaning, and any process sensitive to trace metals; Technical Grade is appropriate for industrial cleaning, latex stabilization, agricultural ammonia, and most cleaning-product manufacture.
How long does ammonium hydroxide last in storage?
2–3 years in original sealed packaging, stored cool and dark. Once opened, ammonia escapes preferentially every time the cap is loosened — a poorly resealed bottle in a warm warehouse can lose 1–2% concentration per month. For long shelf life, buy smaller pack sizes you’ll consume within 6 months of opening, and store unopened reserve stock cool and tightly sealed.
Can ammonium hydroxide be shipped by air?
No. 29% NH₄OH is DOT Class 8 (corrosive) and is restricted to ground transportation in the United States. International ocean freight is allowed under IMO regulations but air freight is generally prohibited at this concentration. For domestic orders, expect ground LTL transit times of 2–5 business days continental US.
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