hydrochloric acid
Enable an AI agent to recognise an aqueous hydrochloric acid material, assess its composition and condition, and determine which uses, transfers or restrictions are justified by the available evidence.
Research draft, second pass
A second pass drafted this model: the structure a model of this thing needs, and what is known about it in the world. The line under this one says how the second half was obtained - researched against sources, or recalled without web access, in which case nothing here was read anywhere and every claim is a lead to verify. Unreviewed either way.
Researched by: Codex + Grok
Purpose and description
Enable an AI agent to recognise an aqueous hydrochloric acid material, assess its composition and condition, and determine which uses, transfers or restrictions are justified by the available evidence.
Aqueous hydrogen chloride (HCl(aq)), a strong monoprotic mineral acid whose practical identity is the concentration and grade of the water-HCl mixture rather than the anhydrous gas.
It can be Identify and label an aqueous hydrochloric acid material using composition and provenance evidence.; Compare concentration and impurity results with the requirements of a stated use.; Flag incompatible contact materials or proposed mixing partners for review.; Determine whether a proposed transfer or use has adequate material-specific evidence and procedural authorisation.; Request qualified sampling or reassessment when identity, concentration or condition is uncertain.; Restrict or quarantine material whose composition, contamination history or use suitability is unresolved..
Distinguishing features
Establish that the material is hydrogen chloride dissolved in water; a hydrogen chloride identifier alone does not distinguish hydrochloric acid from anhydrous hydrogen chloride.
Require evidence for both hydrochloric acidity and chloride-containing composition; low pH alone also describes other acids.
Distinguish hydrochloric acid from chloride salt solutions: chloride detection alone does not establish that hydrogen chloride is the defining acidic component.
Treat 'muriatic acid' as a possible commercial name for hydrochloric acid, then verify concentration and additives rather than assigning a different substance identity.
Distinguish hydrochloric acid from mixed-acid formulations and spent process liquors by establishing whether other acids, dissolved reaction products or additives now define the material's behaviour.
Scope
+ Identification of aqueous hydrogen chloride as hydrochloric acid
+ Hydrogen chloride concentration, reporting basis and compositional uncertainty
+ Grade, impurities, additives and changes caused by use or storage
+ Physical condition and concentration-dependent behaviour
+ Chemical compatibility and suitability for an identified intended use
- Anhydrous hydrogen chloride gas and liquefied hydrogen chloride
- Equipment, containers and storage facilities as independently managed assets
- Manufacturing, dilution, cleaning and neutralisation procedures
- Human exposure, clinical treatment and occupational health records
- Transport consignments, permits and waste-management workflows
Characteristics
- Aqueous hydrochloric acid identity
- confirmed | provisionally identified | unresolved | outside scope Prevents names, acidity or chloride content alone from establishing an unsupported material identity.
- Hydrogen chloride content
- mass fraction as % w/w, or another explicitly stated basis; include method, date and uncertainty Concentration governs use suitability and strongly affects relevant physical and chemical behaviour.
- Amount concentration
- mol/L with solution temperature and measured or derived status Supports quantity-dependent assessment while exposing assumptions in conversions from mass fraction.
- Temperature
- °C Provides context for density, volume-based concentration, vapour behaviour and compatibility assessments.
- Density
- kg/m³ or g/mL at a stated temperature Supports consistency checks and conversions, but cannot establish concentration without suitable composition assumptions.
- Acidity measurement
- pH or titratable acidity, with method and any sample dilution explicitly recorded Distinguishes observed acidity from hydrogen chloride content and avoids overinterpreting pH in concentrated solutions.
- Grade and conformance
- supplier-declared grade, governing specification and conformance status A grade claim is useful only when linked to the impurity limits and evidence needed for the intended use.
- Impurity and additive profile
- identified constituent concentrations in mg/kg, mg/L or another stated basis; include detection limits Metals, other acids and intentional additives can change suitability, reactivity and interpretation of analytical results.
- Observed material condition
- appearance, colour, clarity, solids and reported fuming, with observation conditions Changes may indicate contamination or altered composition without uniquely diagnosing their cause.
- Contact-material compatibility
- specific contacting material linked to concentration, temperature, exposure duration and supporting assessment Compatibility cannot safely be inferred from a broad material label alone.
- Intended-use disposition
- unassessed | supported for stated use | restricted | quarantined | rejected Makes action eligibility depend on explicit requirements and current evidence.
Where this came from
wikidata · CC0 1.0
Also registered as vr.tr.hydrochloric-acid
Drafted structure
Bundle to layer to finding to question, as the second pass will find it: 6 bundles · 11 layers · 18 findings · 28 questions.
Aqueous acid identity Establish whether the material is hydrochloric acid and where that classification stops.
Hydrochloric acid can be confused with anhydrous hydrogen chloride, other acidic liquids and chloride-containing solutions.
Aqueous hydrogen chloride
Connect the material's name to evidence of its defining aqueous composition.
Identity evidence
The agent must distinguish a supported aqueous hydrochloric acid identity from an unverified label.
- What evidence establishes that this material is hydrogen chloride dissolved in water? definition
- Which supplier record or analytical result supports the identity, and does it apply to this batch? provenance
Mixture boundaries
Resolve commercial names and compositions that may require a neighbouring mixture model.
Commercial and process boundary
Names such as muriatic acid do not settle composition, and use can turn hydrochloric acid into a materially different process mixture.
- Does a commercial name denote aqueous hydrochloric acid alone or a formulation with behaviour-changing additives? definition
- Do other acids or accumulated reaction products require classification under a mixed-acid or process-liquor model? boundary
Concentration and analytical basis Record hydrochloric acid strength without confusing concentration conventions or analytical proxies.
A percentage, pH or acidity result cannot be interpreted reliably without its basis and measurement context.
Hydrogen chloride content
Capture the amount of hydrogen chloride represented by the reported concentration.
Concentration basis
Every concentration claim must distinguish its reporting basis and whether it was measured, specified or calculated.
- What is the hydrogen chloride concentration, and is it expressed as mass fraction, amount per volume or another defined basis? measurement
- If the value was converted, which density, temperature and composition assumptions support that conversion? provenance
Analytical interpretation
Determine what acidity, chloride and density observations actually establish.
Limits of analytical proxies
Acidity and chloride results need interpretation when other acids, salts or additives may be present.
- Does the analytical method distinguish hydrogen chloride content from total acidity or total chloride? measurement
- Which sample preparation, interfering constituents or measurement limitations affect confidence in the reported result? boundary
Grade and material condition Assess purity claims and whether the current material still matches its documented composition.
Hydrochloric acid of the correct nominal concentration may still be unsuitable because of impurities, additives or changes during storage and use.
Grade and constituents
Link grade names to explicit limits and batch-specific evidence.
Purity and additive evidence
The model must expose the constituents and specification limits that matter for the proposed application.
- Which specification defines the claimed grade, including relevant impurity limits? provenance
- Which impurities and intentional additives were measured or declared, and which remain unassessed? measurement
Condition and change
Relate present observations to events that could alter the acid.
Composition drift
Dilution, evaporation, contamination and prior reactions can invalidate an earlier composition claim.
- What changes in appearance, solids or analytical results have been observed since the last accepted assessment? measurement
- What storage, opening, transfer or use history could have changed hydrogen chloride content or introduced contaminants? provenance
Reactivity and contact compatibility Represent the chemical interactions that constrain contact, mixing and handling decisions.
Hydrochloric acid can generate heat or hazardous gases through particular interactions, and its compatibility depends on conditions.
Mixing and reaction partners
Identify proposed interactions requiring a specific hazard assessment.
Reaction-specific action boundaries
The agent must account for heat during dilution or neutralisation, potential hydrogen generation with susceptible metals and potential chlorine generation with hypochlorites.
- Which proposed contact or mixing partners introduce heat, gas evolution or other hazardous reaction concerns? boundary
- What material-specific assessment and authorised procedure are required before the proposed interaction may proceed? action
Wetted materials and vapour
Assess contact surfaces and potential release behaviour under the actual conditions.
Conditional compatibility
A compatibility claim must address the actual contacting material, acid composition and exposure conditions.
- What evidence supports compatibility of the proposed contacting materials at this concentration, temperature and duration? provenance
- What assessment of hydrogen chloride vapour or acid mist release constrains the proposed handling conditions? boundary
Use suitability and disposition Translate identity, composition and compatibility evidence into a bounded material-use decision.
Recognising hydrochloric acid does not establish that a particular batch is suitable for a particular application.
Application requirements
Compare the actual material with the chemical requirements of its intended use.
Application-specific fit
Suitability must reference acceptable concentration, impurity limits and additive restrictions for an identified application.
- What concentration range, impurity limits and additive restrictions apply to the intended use? boundary
- Does current batch evidence satisfy those requirements, and which gaps prevent a supported decision? action
Release and reassessment
Record a use decision and the events that invalidate it.
Bounded material disposition
Approval applies to a stated material condition and use; unresolved identity or composition requires an explicit restriction.
- Is this material supported for the stated use, restricted, quarantined or rejected, and what evidence supports that disposition? action
- Which events, such as dilution, contamination, return from a process or changed contact conditions, require reassessment? boundary
Evidence and external alignment What the world already says about this thing, gathered so the model can be checked against it.
A model that cannot be lined up against existing standards, identifiers and practice cannot be adopted by anyone who already uses them.
Reported evidence
Findings from the breadth pass, kept separate from the structural claims.
Kinds and varieties
Reported by the breadth pass; each item needs checking against its source before it becomes normative.
- technical/industrial grade
- reagent/ACS grade
- food-grade (E507)
- pharmaceutical/USP grade
- muriatic acid (trade name for dilute industrial HCl)
- fuming/concentrated (~37% w/w)
- dilute process acid
- hydrogen chloride gas (anhydrous HCl, neighbouring substance)
- Which of these kinds and varieties hold for the sense of hydrochloric acid this model covers, and on what evidence? provenance
Identifiers and schemes
Reported by the breadth pass; each item needs checking against its source before it becomes normative.
- CAS - 7647-01-0 - Hydrogen chloride / hydrochloric acid
- Which of these identifiers and schemes hold for the sense of hydrochloric acid this model covers, and on what evidence? provenance
Standards and regulation
Reported by the breadth pass; each item needs checking against its source before it becomes normative.
- UN 1789 (hydrochloric acid solution)
- Which of these standards and regulation hold for the sense of hydrochloric acid this model covers, and on what evidence? provenance
Real-world use
Reported by the breadth pass; each item needs checking against its source before it becomes normative.
- Steel pickling
- pH control
- chemical synthesis
- Which of these real-world use hold for the sense of hydrochloric acid this model covers, and on what evidence? provenance
Typical measurements
Reported by the breadth pass; each item needs checking against its source before it becomes normative.
- concentration - 10-38 - % w/w
- Which of these typical measurements hold for the sense of hydrochloric acid this model covers, and on what evidence? provenance
Failure modes and hazards
Reported by the breadth pass; each item needs checking against its source before it becomes normative.
- Corrosive burns
- HCl vapour inhalation
- Which of these failure modes and hazards hold for the sense of hydrochloric acid this model covers, and on what evidence? provenance
Regional variation
Reported by the breadth pass; each item needs checking against its source before it becomes normative.
- Muriatic acid in North America for pool/masonry use
- Which of these regional variation hold for the sense of hydrochloric acid this model covers, and on what evidence? provenance
Neighbouring kinds and how to tell them apart
Reported by the breadth pass; each item needs checking against its source before it becomes normative.
- sulfuric acid - HCl is a volatile hydrogen halide; H2SO4 is non-volatile and dehydrating
- Which of these neighbouring kinds and how to tell them apart hold for the sense of hydrochloric acid this model covers, and on what evidence? provenance
Sources
- Hydrochloric acid - Identity, formula, CAS, concentration ranges
What the second pass must settle
- What registry boundary should separate additive-containing hydrochloric acid products and spent acid liquors from independently modelled mixtures?
- Which authoritative grade specifications and impurity limits should be supported for the intended applications?
- Which analytical methods reliably establish hydrogen chloride content across the concentrations and interfering constituents this model must cover?
- Which validated sources provide applicable physical-property, vapour-behaviour and contact-material compatibility data, and what are their limits?
- What evidence and reassessment criteria are required to retain a use disposition after prolonged storage, opening or transfer?