Molar Mass of Sodium Hydroxide (NaOH)
Learn how chemists calculate the molar mass of Sodium Hydroxide (NaOH), with a clear formula breakdown, worked steps, and study notes · IUPAC name: Sodium hydroxide.
Quick answer
The molar mass of Sodium Hydroxide (NaOH) is
39.997g/mol
One mole of Sodium Hydroxide therefore has a mass of 39.997 grams—the value you use for stoichiometry and laboratory preparation.
Reviewed for educational accuracy · Accuracy policy
- CAS Registry Number
- 1310-73-2
- PubChem CID
- 14798
- SMILES
- [OH-].[Na+]
Step-by-step calculation
Let's find the molar mass of Sodium Hydroxide (NaOH) together—step by step, as if you are seeing the formula for the first time.
Step 1 — Look at the chemical formula
The formula is NaOH. Each letter stands for an element. The little number after a letter (the subscript) tells you how many atoms of that element are in one molecule or formula unit.
- 1 Sodium atom (Na)
- 1 Oxygen atom (O)
- 1 Hydrogen atom (H)
Step 2 — Look up each atomic mass
Atomic mass comes from the periodic table. It is the average mass of one mole of atoms of that element, in grams per mole (g/mol). Think of it as the "price tag" for one mole of that element.
- Sodium (Na) = 22.990 g/mol
- Oxygen (O) = 15.999 g/mol
- Hydrogen (H) = 1.008 g/mol
Step 3 — Multiply atoms × atomic mass
Why multiply? If one oxygen atom "costs" about 16 g/mol, then two oxygen atoms cost twice as much. Each element's contribution is: number of atoms × atomic mass.
- 1 × 22.990 = 22.990 g/mol (Sodium)
- 1 × 15.999 = 15.999 g/mol (Oxygen)
- 1 × 1.008 = 1.008 g/mol (Hydrogen)
Step 4 — Add the contributions
Why add? The molar mass of the whole compound is simply the total mass of every atom in the formula. Add each element's contribution:
22.990 + 15.999 + 1.008 = 39.997 g/mol
Step 5 — Final answer
Molar mass of Sodium Hydroxide = 39.997 g/mol
That means one mole of Sodium Hydroxide (NaOH) has a mass of about 40.00 grams.
Quick summary
Read the formula → count atoms → look up atomic masses → multiply → add → report g/mol. For NaOH, the total is 39.997 g/mol.
Common beginner mistakes
- Confusing NaOH (40 g/mol) with Na₂O (62 g/mol) or Na₂CO₃ (106 g/mol).
- Using NaOH molar mass when calculating moles of OH⁻ from Ca(OH)₂ (which provides 2 OH⁻ per formula unit).
- Storing NaOH in glass bottles long-term (attacks glass at high concentration).
Memory trick
Round 40.00 g/mol to 40 for mental math in titration problems.
Mini practice
Without looking above, list the atoms in NaOH and write one multiplication line for the heaviest element. Then check your work against Step 3.
Real-world example
If a recipe asks for 0.100 mol of Sodium Hydroxide, mass needed = 0.100 × 39.997 = 4.000 g. That is how chemists turn a mole amount into a weighable sample.
Atomic contribution table
Each row shows how much mass one element contributes to the total for NaOH.
| Element | Atoms | Atomic mass | Contribution | Mass % |
|---|---|---|---|---|
| Na | 1 | 22.990 | 22.990 g/mol | 57.5% |
| O | 1 | 15.999 | 15.999 g/mol | 40.0% |
| H | 1 | 1.008 | 1.008 g/mol | 2.5% |
| Total molar mass | 39.997 g/mol | 100% | ||
Mass contribution chart
Count every atom in this formula, multiply by atomic mass, then add. That total is the molar mass used in lab weighing.
Download study sheets
Save a printable summary, revision sheet, practice worksheet, or laboratory reference for Sodium Hydroxide (NaOH).
Practice this calculation
Without looking above, write the atom count for NaOH, then compute the molar mass. Check your answer against 39.997 g/mol.
Next challenge: how many grams are in 0.250 mol of Sodium Hydroxide? Multiply 0.250 × 39.997 to get 9.999 g.
Physical and chemical properties
Physical properties
| Appearance | White pellets, flakes, or granules (solid); colorless solution |
| Color | White (solid) |
| Odor | Odorless |
| State (STP) | Solid (deliquescent) |
| Density | 2.13 g/cm³ (solid); solution density varies with concentration |
| Melting point | 318 °C |
| Boiling point | 1,388 °C |
| Solubility | 1110 g/L water at 20 °C (highly soluble, exothermic) |
| Crystal structure | Orthorhombic (β-NaOH); monoclinic (α-NaOH, <299 °C) |
Chemical properties
| Classification | Strong base / alkali metal hydroxide |
| Family | Group 1 hydroxide (alkali hydroxide) |
| Basicity | Strong base (pKb ≈ 0.2 for OH⁻) |
| Polarity | Ionic compound; OH⁻ highly polar |
| Oxidation states | Na: +1, O: −2, H: +1 |
Applications
Industrial uses
- Soap and detergent manufacturing (saponification of fats)
- Pulp and paper processing (Kraft process for lignin removal)
- Petroleum refining (mercaptan removal)
- Aluminum ore processing (Bayer process)
- pH adjustment in water treatment and food processing
Laboratory uses
- Standard strong base for acid–base titrations
- Preparation of buffer solutions (with weak acids)
- Qualitative analysis — precipitating metal hydroxides
Used in scrubbers to neutralize acidic industrial effluents and in biodiesel production to remove free fatty acids.
Not used biologically; highly destructive to tissue — dissolves proteins and lipids in skin (chemical burn mechanism).
Preparation and production
Electrolysis of NaCl brine (chlor-alkali process) is the industrial route. Laboratory: react calcium hydroxide with sodium carbonate (Na₂CO₃ + Ca(OH)₂ → 2 NaOH + CaCO₃), or purchase reagent pellets.
Global production exceeds 70 million tonnes annually. Membrane cell technology dominates new installations for lower energy use and avoidance of mercury contamination.
Important reactions of Sodium Hydroxide
NaOH(aq) + HCl(aq) → NaCl(aq) + H₂O(l)
- Reaction type
- Acid–base neutralization
- Conditions
- Aqueous, equimolar
- Explanation
- Classic strong acid–strong base reaction producing salt and water with neutralization enthalpy ~−57 kJ/mol.
- Products
- Sodium chloride and water
- Why it matters
- Titrations, pH adjustment, salt production
Related ideas: Neutralization · Titration · Stoichiometry
2 NaOH(aq) + CO₂(g) → Na₂CO₃(aq) + H₂O(l)
- Reaction type
- Acid–base (with acidic oxide)
- Conditions
- Aqueous NaOH, CO₂ gas
- Explanation
- Sodium hydroxide scrubs CO₂ by forming carbonate; with excess CO₂, bicarbonate forms.
- Products
- Sodium carbonate and water
- Why it matters
- CO₂ absorption, air purification, understanding NaOH degradation on air exposure
Related ideas: Acidic oxides · Gas scrubbing · Carbon cycle
Fat + 3 NaOH → Glycerol + 3 R-COO⁻Na⁺ (soap)
- Reaction type
- Saponification (hydrolysis)
- Conditions
- Heat, aqueous NaOH
- Explanation
- Triglyceride ester bonds hydrolyze to glycerol and sodium salts of fatty acids (soap).
- Products
- Glycerol and soap
- Why it matters
- Soap manufacturing, biodiesel byproduct treatment
Related ideas: Ester hydrolysis · Organic chemistry · Colloids
FeCl₃(aq) + 3 NaOH(aq) → Fe(OH)₃(s) + 3 NaCl(aq)
- Reaction type
- Precipitation
- Conditions
- Aqueous, room temperature
- Explanation
- Metal ions precipitate as insoluble hydroxides — iron(III) forms reddish-brown Fe(OH)₃ gel.
- Products
- Iron(III) hydroxide precipitate
- Why it matters
- Water treatment (phosphate/suspended solids removal), qualitative analysis
Related ideas: Solubility rules · Precipitation · Qualitative analysis
History and discovery
LeBlanc process (late 18th century) produced Na₂CO₃, from which NaOH could be prepared. The chlor-alkali process (late 19th century) revolutionized direct NaOH production. Castner-Kellner mercury cell (1892) and modern membrane cells improved efficiency and environmental safety.
Humphry Davy isolated sodium metal (1807); NaOH as ionic compound understood through electrolysis and Arrhenius ionic theory.
Interesting facts
- NaOH molar mass ~40 g/mol makes 40 g exactly 1 mole — convenient for quick calculations.
- Drain cleaners often contain 30–50% NaOH to dissolve grease and hair (protein hydrolysis).
- The slippery feel of NaOH on skin is due to saponification of fatty acids in the skin.
- NaOH was historically called caustic soda to distinguish from caustic potash (KOH).
Comparison with similar compounds
NaOH (40.00 g/mol) and KOH (56.11 g/mol) are both strong bases; KOH is more soluble in alcohols and used in soft soap, while NaOH dominates hard soap production.
Storage, handling, and safety
Store in airtight, corrosion-resistant containers (HDPE). Keep dry — pellets absorb CO₂ forming Na₂CO₃ on exposure. Separate from acids and aluminum.
Extremely corrosive. Wear nitrile or neoprene gloves, chemical splash goggles, and face shield. Add NaOH slowly to water (still exothermic). Never handle with bare hands — slippery feel indicates skin saponification has begun.
Severe corrosive hazard to skin, eyes, and respiratory tract. Generates heat when dissolved in water.
- Chemical burns — may be deeper than apparent initially
- Eye damage leading to permanent blindness
- Exothermic dissolution can cause boiling and splashing
- Reacts with aluminum to produce hydrogen gas
Classification: GHS: Skin Corr. 1A, Eye Dam. 1
Exam notes and student tips
Exam notes
- Molar mass NaOH = 22.99 + 16.00 + 1.008 = 40.00 g/mol.
- Strong base: 1 mol NaOH neutralizes 1 mol HCl (monoprotic acid).
- For H₂SO₄: 2 mol NaOH per mol acid (diprotic).
- NaOH absorbs CO₂: 2 NaOH + CO₂ → Na₂CO₃ + H₂O — relevant to storage and air exposure.
Student tips
- Round 40.00 g/mol to 40 for mental math in titration problems.
- Standardize NaOH titrant against potassium hydrogen phthalate (KHP) — know this lab procedure.
- Link to saponification: fat + 3 NaOH → glycerol + 3 soap molecules.
Common mistakes
- Confusing NaOH (40 g/mol) with Na₂O (62 g/mol) or Na₂CO₃ (106 g/mol).
- Using NaOH molar mass when calculating moles of OH⁻ from Ca(OH)₂ (which provides 2 OH⁻ per formula unit).
- Storing NaOH in glass bottles long-term (attacks glass at high concentration).
Misconceptions
- NaOH is not the same as sodium oxide (Na₂O) — adding water to Na₂O gives NaOH.
- Dilute NaOH is still corrosive; dilution reduces but does not eliminate hazard.
- NaOH does not contain molecular 'NaOH' units in solution — it is fully ionized.
Practice questions
1. Calculate the molar mass of NaOH.
Show answer
22.99 + 16.00 + 1.008 = 40.00 g/mol
2. How many grams of NaOH to neutralize 36.5 g of HCl?
Show answer
36.5 g HCl ÷ 36.46 g/mol = 1.0 mol HCl; need 1.0 mol NaOH = 40.0 g
3. What pH range is expected for 0.1 M NaOH?
Show answer
pOH = 1, so pH = 14 − 1 = 13 (strong base, complete dissociation assumed)
4. Why does NaOH feel slippery on skin?
Show answer
It saponifies fatty acids in skin tissue, forming soap which feels slippery.
Frequently asked questions about Sodium Hydroxide
40.00 g/mol.
Chemistry of Sodium Hydroxide
The sections above give the number you need for calculations. Here we look more closely at how Sodium Hydroxide (NaOH) behaves chemically—so the molar mass connects to real reactions, properties, and laboratory practice.
Sodium hydroxide (NaOH) is a strong base with molar mass 40.00 g/mol (Na 22.99 + O 16.00 + H 1.008). It dissociates completely in water to Na⁺ and OH⁻, giving pH values above 13 for concentrated solutions. NaOH is hygroscopic and deliquescent — it absorbs moisture from air until dissolving — and reacts exothermically with water (ΔH ≈ −44 kJ/mol dissolution).
NaOH is produced at massive scale by the chlor-alkali process alongside chlorine and hydrogen from brine electrolysis. Its ability to saponify triglycerides (breaking ester bonds to form soap and glycerol) has made it central to soap manufacturing for centuries. In chemistry education, NaOH is the standard strong base for titrations against HCl and for adjusting pH in countless reactions.
NaOH consists of Na⁺ and OH⁻ ions. In solid form it exists as an ionic lattice; in solution the hydroxide ion is the active base species. The formula shows a 1:1 ratio of sodium to hydroxide, distinguishing it from dibasic bases like Ca(OH)₂.
NaOH is a Brønsted base (proton acceptor) and Lewis base. It neutralizes acids, precipitates metal hydroxides from salt solutions (e.g., Fe³⁺ + 3 OH⁻ → Fe(OH)₃), and attacks amphoteric aluminum and zinc oxides. Hot concentrated NaOH reacts with aluminum metal: 2 Al + 2 NaOH + 6 H₂O → 2 Na[Al(OH)₄] + 3 H₂. It corrodes glass (attacks silica) over time — store in polyethylene, not glass, for long periods.
Saponification chemistry: from fats to soap
Saponifying a triglyceride with sodium hydroxide hydrolyzes each of its three ester bonds, releasing glycerol and three sodium salts of long-chain fatty acids — soap. The sodium carboxylate 'head' is hydrophilic while the long hydrocarbon 'tail' is hydrophobic, and this dual character is exactly what allows soap micelles to surround and lift away oily grime, making NaOH-based saponification the chemical foundation of traditional bar soap manufacturing.
The chlor-alkali process: NaOH as a co-product of chlorine production
Nearly all industrial sodium hydroxide is produced as a co-product of chlorine gas manufacture through electrolysis of saturated brine, meaning NaOH supply and price are tightly linked to chlorine demand (and vice versa) rather than being independently driven by hydroxide demand alone — an important economic and industrial chemistry link that explains fluctuations in caustic soda markets tracking the chlorine/PVC industry.
NaOH vs. KOH: solubility, cost, and application divide
Although sodium hydroxide and potassium hydroxide are both strong Group 1 hydroxides with nearly identical acid–base chemistry, NaOH is cheaper and dominates large-scale industrial uses like pulp processing and hard bar soap manufacture, while KOH's superior solubility in alcohols makes it preferred for biodiesel transesterification and for producing softer, more liquid potassium-based soaps — a clear case of practical solubility differences, not intrinsic base strength, driving industrial compound choice.
Drain and oven cleaner chemistry: hydrolyzing grease and protein
NaOH's aggressive hydrolysis of both ester bonds (in fats and grease) and amide/peptide bonds (in proteins like hair) is precisely why it is the active ingredient in many drain cleaners and oven cleaners — it chemically dissolves the organic clogs and baked-on residue that mechanical cleaning alone struggles to remove, though this same tissue-dissolving power is what makes concentrated NaOH so hazardous to skin and eyes.
Recalculate any formula with the molar mass calculator, compare atoms on the periodic table, or browse more compounds in the base library.
References and further reading
- ILO Encyclopaedia: Occupational safety for caustic soda
- NIST Chemistry WebBook: Thermodynamic properties
- PubChem CID 14798: Compound data