Molar Mass of Hydrochloric Acid (HCl)
Learn how chemists calculate the molar mass of Hydrochloric Acid (HCl), with a clear formula breakdown, worked steps, and study notes · IUPAC name: Hydrogen chloride (gas); Hydrochloric acid (aqueous).
Quick answer
The molar mass of Hydrochloric Acid (HCl) is
36.458g/mol
One mole of Hydrochloric Acid therefore has a mass of 36.458 grams—the value you use for stoichiometry and laboratory preparation.
Reviewed for educational accuracy · Accuracy policy
- CAS Registry Number
- 7647-01-0
- PubChem CID
- 313
- SMILES
- Cl
Step-by-step calculation
Let's find the molar mass of Hydrochloric Acid (HCl) 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 HCl. 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 Hydrogen atom (H)
- 1 Chlorine atom (Cl)
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.
- Hydrogen (H) = 1.008 g/mol
- Chlorine (Cl) = 35.450 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 × 1.008 = 1.008 g/mol (Hydrogen)
- 1 × 35.450 = 35.450 g/mol (Chlorine)
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:
1.008 + 35.450 = 36.458 g/mol
Step 5 — Final answer
Molar mass of Hydrochloric Acid = 36.458 g/mol
That means one mole of Hydrochloric Acid (HCl) has a mass of about 36.46 grams.
Quick summary
Read the formula → count atoms → look up atomic masses → multiply → add → report g/mol. For HCl, the total is 36.458 g/mol.
Common beginner mistakes
- Confusing HCl (36.46 g/mol) with Cl₂ (70.90 g/mol).
- Expecting Cu to react with dilute HCl (copper is below H in activity series for non-oxidizing acid).
- Writing HCl as ionic in gas phase — it is covalent until dissolved in water.
Memory trick
Round 36.46 to 36.5 for quick stoichiometry.
Mini practice
Without looking above, list the atoms in HCl 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 Hydrochloric Acid, mass needed = 0.100 × 36.458 = 3.646 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 HCl.
| Element | Atoms | Atomic mass | Contribution | Mass % |
|---|---|---|---|---|
| H | 1 | 1.008 | 1.008 g/mol | 2.8% |
| Cl | 1 | 35.450 | 35.450 g/mol | 97.2% |
| Total molar mass | 36.458 g/mol | 100% | ||
Mass contribution chart
In water, many acids transfer H⁺ (a proton) to form hydronium. Molar mass still comes from the undissociated formula used to prepare the solution.
Download study sheets
Save a printable summary, revision sheet, practice worksheet, or laboratory reference for Hydrochloric Acid (HCl).
Practice this calculation
Without looking above, write the atom count for HCl, then compute the molar mass. Check your answer against 36.458 g/mol.
Next challenge: how many grams are in 0.250 mol of Hydrochloric Acid? Multiply 0.250 × 36.458 to get 9.115 g.
Physical and chemical properties
Physical properties
| Appearance | Colorless to pale yellow liquid (solution); colorless gas (anhydrous) |
| Color | Colorless |
| Odor | Pungent, irritating (solution fumes) |
| State (STP) | Gas (anhydrous HCl); liquid (concentrated aqueous solution) |
| Density | 1.18 g/mL (37% solution, 20 °C); gas 1.639 g/L at 0 °C |
| Melting point | −114.2 °C (anhydrous HCl) |
| Boiling point | −85.1 °C (anhydrous HCl); azeotrope ~20.2% boils at 108.6 °C |
| Solubility | 720 g/L water at 20 °C (gas dissolves extensively, fuming) |
| Crystal structure | Not applicable (gas/liquid); ionic character in aqueous solution only |
Chemical properties
| Classification | Mineral acid / strong monoprotic acid |
| Family | Hydrogen halide (strongest common halide acid in water) |
| Acidity | Strong acid (pKa ≈ −7) |
| Polarity | Polar covalent (gas); ionic in aqueous solution |
| Geometry | Linear (gas phase HCl) |
| Bond angle | 180° |
| Oxidation states | H: +1, Cl: −1 |
Applications
Industrial uses
- Steel pickling (removing rust and scale before galvanizing)
- Production of PVC via vinyl chloride monomer synthesis
- Food-grade acidulant and pH regulator (E507)
- Oil well acidizing (dissolving carbonate formations)
Laboratory uses
- Strong acid titrations against NaOH
- Preparation of chloride salts (HCl + metal/base → chloride)
- Cleaning glassware (removes mineral deposits)
Gastric acid component for digestion and pathogen defense; pathologically associated with GERD and peptic ulcers (often linked to H. pylori, not acid alone).
Preparation and production
Direct synthesis: H₂ + Cl₂ → 2 HCl (industrial, exothermic). Laboratory: NaCl + H₂SO₄ (conc.) → NaHSO₄ + HCl↑. Aqueous HCl prepared by bubbling HCl gas into water in fume hood.
Co-product of chlor-alkali industry; also synthesized directly from elements. Global HCl market tied to PVC, steel, and chemical synthesis demand.
Important reactions of Hydrochloric Acid
HCl(aq) + NaOH(aq) → NaCl(aq) + H₂O(l)
- Reaction type
- Acid–base neutralization
- Conditions
- Aqueous, standard titration
- Explanation
- Strong acid–strong base neutralization with sharp phenolphthalein endpoint.
- Products
- Sodium chloride and water
- Why it matters
- Acid–base titrations, salt preparation
Related ideas: Titration · Neutralization · Equivalence point
Zn(s) + 2 HCl(aq) → ZnCl₂(aq) + H₂(g)
- Reaction type
- Single displacement
- Conditions
- Dilute HCl, room temperature
- Explanation
- Zinc reduces H⁺ to H₂ gas; zinc oxidizes to Zn²⁺. Classic lab gas preparation.
- Products
- Zinc chloride and hydrogen gas
- Why it matters
- Hydrogen generation, demonstrating acid–metal reactivity
Related ideas: Activity series · Redox · Gas stoichiometry
CaCO₃(s) + 2 HCl(aq) → CaCl₂(aq) + H₂O(l) + CO₂(g)
- Reaction type
- Acid–carbonate
- Conditions
- Room temperature, aqueous
- Explanation
- Carbonates react with acid to release CO₂ — effervescence indicates carbonate or bicarbonate.
- Products
- Calcium chloride, water, carbon dioxide
- Why it matters
- CO₂ preparation, carbonate identification, antacid chemistry (CaCO₃ neutralizes HCl)
Related ideas: Gas evolution · Antacids · Qualitative analysis
MnO₂(s) + 4 HCl(conc) → MnCl₂(aq) + Cl₂(g) + 2 H₂O(l)
- Reaction type
- Redox
- Conditions
- Concentrated HCl, heat
- Explanation
- Manganese(IV) oxide oxidizes chloride to chlorine gas; HCl acts as reductant.
- Products
- Manganese(II) chloride, chlorine, water
- Why it matters
- Chlorine preparation in laboratory
Related ideas: Redox · Oxidizing agents · Halogen chemistry
History and discovery
Alchemists prepared HCl from salt and vitriol. Priestley collected HCl gas over mercury (1772). Davy proved HCl was a compound of hydrogen and chlorine (1810). Industrial synthesis from H₂ and Cl₂ developed in the 19th century with chlorine chemistry expansion.
Carl Wilhelm Scheele and Joseph Priestley independently characterized hydrogen chloride gas in the 1770s.
Interesting facts
- Muriatic acid (from Latin muria, brine) was historically produced from salt and sulfuric acid.
- The molar mass 36.46 g/mol means 36.46 g HCl gas occupies 22.4 L at STP.
- HCl secretion in stomach totals roughly 1.5–2 L of 0.5% acid daily.
- Aqua regia (3 HCl : 1 HNO₃) can dissolve gold — neither acid alone can.
Comparison with similar compounds
HCl (36.46 g/mol) is monoprotic and non-oxidizing; H₂SO₄ (98.08 g/mol) is diprotic and dehydrating; HNO₃ (63.01 g/mol) is monoprotic but oxidizing.
Storage, handling, and safety
Store in corrosion-resistant containers (glass, certain plastics, rubber-lined steel). Vent gas space — HCl fumes corrode nearby metal. Keep away from bases and moisture-sensitive materials.
Corrosive and releases irritating HCl fumes. Use fume hood. Acid-resistant gloves and eye protection mandatory. Never mix with bleach (releases toxic Cl₂).
Corrosive to skin, eyes, and respiratory tract. Inhalation causes coughing and pulmonary edema at high concentrations.
- Corrosive burns
- Toxic fume inhalation
- Violent reaction with bases (heat generation)
- Cl₂ release if mixed with oxidizers or bleach
Classification: GHS: Skin Corr. 1B, Eye Dam. 1
Exam notes and student tips
Exam notes
- Molar mass HCl = 1.008 + 35.45 = 36.46 g/mol.
- Monoprotic strong acid: 1 mol HCl = 1 mol H⁺ for neutralization.
- Test for chloride: AgNO₃ + Cl⁻ → AgCl(s) white, darkens in light.
- Metal + acid: Mg + 2 HCl → MgCl₂ + H₂ (balance and calculate gas volume at STP).
Student tips
- Round 36.46 to 36.5 for quick stoichiometry.
- Remember HCl + carbonate always gives CO₂ — useful identification test.
- For titrations: moles HCl = moles NaOH at equivalence (1:1).
Common mistakes
- Confusing HCl (36.46 g/mol) with Cl₂ (70.90 g/mol).
- Expecting Cu to react with dilute HCl (copper is below H in activity series for non-oxidizing acid).
- Writing HCl as ionic in gas phase — it is covalent until dissolved in water.
Misconceptions
- Stomach acid is not pure HCl — it contains KCl, NaCl, and mucus.
- HCl does not oxidize metals to higher oxides the way HNO₃ does.
- Muriatic acid from hardware stores is impure HCl — same core chemistry, variable concentration.
Practice questions
1. Calculate the molar mass of HCl.
Show answer
1.008 + 35.45 = 36.46 g/mol
2. What volume of H₂ at STP from 73 g HCl reacting with excess Zn?
Hint: 2 HCl → 1 H₂ from the balanced equation with Zn.
Show answer
73 g ÷ 36.46 g/mol = 2.0 mol HCl; produces 1.0 mol H₂ = 22.4 L
3. Why doesn't copper react with dilute HCl?
Show answer
Copper is below hydrogen in the activity series; HCl is not a strong enough oxidant to oxidize Cu to Cu²⁺.
4. How many mL of 12 M HCl needed for 0.50 mol HCl?
Show answer
0.50 mol ÷ 12 mol/L = 0.042 L = 42 mL
Frequently asked questions about Hydrochloric Acid
36.46 g/mol for the HCl formula unit.
Chemistry of Hydrochloric Acid
The sections above give the number you need for calculations. Here we look more closely at how Hydrochloric Acid (HCl) behaves chemically—so the molar mass connects to real reactions, properties, and laboratory practice.
Hydrochloric acid (HCl) in aqueous solution is one of the strongest common acids, with molar mass 36.46 g/mol for the hydrogen chloride unit (H 1.008 + Cl 35.45). Anhydrous HCl is a colorless gas that fumes in moist air because it dissolves exothermically in water; commercial "hydrochloric acid" is typically 32–38% HCl by mass (roughly 10–12 M).
HCl dissociates completely in dilute aqueous solution: HCl + H₂O → H₃O⁺ + Cl⁻. The chloride ion is a weak nucleophile and poor oxidizing agent, distinguishing HCl behavior from nitric acid. Gastric juice in humans contains ~0.5% HCl (pH 1–2), providing antimicrobial action and activating pepsin for protein digestion. Stomach acid secretion by parietal cells uses the H⁺/K⁺-ATPase pump with Cl⁻ following passively.
HCl is a diatomic molecule in the gas phase with a polar covalent bond (ΔEN ≈ 0.9). In water it ionizes completely to H₃O⁺ and Cl⁻. The formula represents one proton and one chloride ion per acid unit for stoichiometric purposes.
HCl is a monoprotic strong acid. It reacts with metals above hydrogen in the activity series (Mg, Zn, Fe) producing H₂ gas. With carbonates: 2 HCl + CaCO₃ → CaCl₂ + H₂O + CO₂. It does not oxidize copper or silver — unlike HNO₃. Concentrated HCl is oxidized by MnO₂ or KMnO₄ to release Cl₂ gas. Aqua regia (HCl + HNO₃, 3:1) dissolves gold via chloroaurate complex formation.
Stomach Acid and Digestive Chemistry
Parietal cells in the stomach lining secrete roughly 1.5–2 L of gastric juice daily containing HCl at pH 1–2, using the H⁺/K⁺-ATPase proton pump; this acidity activates pepsinogen into the digestive enzyme pepsin, denatures dietary proteins to expose them for enzymatic cleavage, and kills or suppresses many ingested pathogens — a physiological role that proton-pump inhibitor drugs (like omeprazole) directly target when treating acid reflux.
Industrial Pickling and Metal Cleaning
'Pickling' uses dilute HCl to dissolve rust, mill scale, and oxide layers from steel surfaces before galvanizing, painting, or further processing — HCl + FeO → FeCl₂ + H₂O (schematically) — making it one of the most widely used industrial acids for metal surface preparation despite the corrosive fumes and spent-acid disposal challenges involved.
HCl as a Strong, Non-Oxidizing Acid
HCl dissociates completely in water (strong acid) but, unlike nitric or sulfuric acid, does not act as an oxidizer — its chloride ion is a poor oxidizing agent, so HCl reacts with active metals purely through H⁺ reduction to H₂ gas rather than oxidizing the metal via the acid's anion, a key distinction tested when comparing metal-acid reactions across different mineral acids.
HCl vs. HF: Strong Acid, Simple Hazard vs. Weak Acid, Complex Toxicity
HCl (strong acid, Ka effectively infinite) causes immediate, visible corrosive burns proportional to its concentration and contact time, following conventional acid-hazard expectations. HF, despite being a weak acid, is far more insidiously dangerous because fluoride ion penetrates tissue and binds calcium systemically — a stark illustration that acid strength and overall chemical hazard are not the same thing.
HCl vs. H₂SO₄: Monoprotic vs. Diprotic, Non-Dehydrating vs. Dehydrating
HCl (36.46 g/mol) is monoprotic and lacks meaningful dehydrating or oxidizing power, while H₂SO₄ (98.08 g/mol) is diprotic, a powerful dehydrating agent capable of charring organic matter, and oxidizes some metals when hot and concentrated — differences that matter directly for reaction stoichiometry, safety precautions, and choice of acid in a given synthesis or industrial process.
Recalculate any formula with the molar mass calculator, compare atoms on the periodic table, or browse more compounds in the acid library.
References and further reading
- NIST Chemistry WebBook: HCl thermophysical data
- PubChem CID 313: Hydrogen chloride properties
- IUPAC: Acid nomenclature and strength