The cas number of hydrochloric acid is 7647-01-0. This unique identifier, assigned by the Chemical Abstracts Service, distinguishes hydrochloric acid from all other chemical substances globally.
CAS numbers are standardized identifiers used in scientific literature, safety documentation, and regulatory databases. For hydrochloric acid, the number 7647-01-0 appears on every safety data sheet (SDS), product label, and regulatory filing involving the substance. It is not derived from molecular structure-it is assigned by a central authority to prevent ambiguity.
Hydrochloric acid is a clear, fuming liquid composed of hydrogen chloride gas dissolved in water. Its concentration varies widely-from 10% to 37% by weight in commercial forms. Despite this variation, the CAS number remains unchanged because it identifies the chemical entity, not its concentration or formulation.
CAS numbers follow a three-part format: a prefix, a separator, and a check digit. For 7647-01-0:
This system prevents duplication. No two chemicals share the same CAS number. Even minor structural changes-like adding a methyl group-result in a different identifier. For hydrochloric acid, the number is immutable regardless of purity or packaging.
Regulatory agencies such as the U.S. Environmental Protection Agency (EPA) and the European Chemicals Agency (ECHA) rely on CAS numbers to track chemical exposure, enforce reporting requirements, and manage risk assessments. The EPA's Toxics Release Inventory (TRI) uses 7647-01-0 to identify releases of hydrochloric acid into the environment.
Many assume that CAS numbers change with concentration. They do not. A 10% solution of hydrochloric acid and a 37% solution both carry the same CAS number-7647-01-0. The number identifies the chemical, not its strength or application.
Another frequent error is confusing the CAS number with the molecular formula (HCl) or the name. While HCl is the formula, it is ambiguous-many compounds have similar formulas. The CAS number resolves that ambiguity. For example, "hydrochloric acid" may refer to a solution, while "hydrogen chloride" refers to the gas. Both are assigned different CAS numbers: 7647-01-0 for the acid and 7647-00-9 for the gas.
A third misconception is that CAS numbers are optional. They are not. Under OSHA's Hazard Communication Standard (HCS), all hazardous chemicals must include their CAS number on labels and SDSs. Failure to list it results in non-compliance and potential fines.
The cas number of hydrochloric acid is essential in laboratories, manufacturing, and environmental monitoring. In a research lab, a scientist ordering hydrochloric acid must verify the CAS number to ensure they receive the correct reagent. Using the wrong compound-even a similar acid-can invalidate experiments.
In industry, the number enables compliance with global regulations. The Globally Harmonized System (GHS) mandates that all hazardous chemicals include the CAS number on labels. This allows emergency responders to quickly access toxicity data during spills or exposures.
For example, a warehouse worker handling a drum of 37% hydrochloric acid must consult the SDS. The document lists 7647-01-0 under "Chemical Identification." This entry triggers immediate access to exposure limits, first aid procedures, and spill response protocols. Without the CAS number, this information would be difficult to retrieve accurately.
Understanding the CAS number of hydrochloric acid becomes clearer when compared to other frequently used acids. The table below shows key differences:
| Acid | CAS Number | Common Use | Key Difference |
|---|---|---|---|
| Hydrochloric acid | 7647-01-0 | Industrial cleaning, pH adjustment, metal pickling | Strong mineral acid; highly corrosive; volatile |
| Sulfuric acid | 7664-93-9 | Battery electrolyte, fertilizer production | Dehydrating agent; higher boiling point |
| Isopropyl alcohol | 67-63-0 | Disinfectant, solvent | Organic compound; flammable; less corrosive |
| Citric acid | 77-92-9 | Food additive, chelating agent | Natural organic acid; low toxicity |
Each acid has a distinct CAS number. Confusing them leads to errors. For instance, mixing sulfuric acid (7664-93-9) with hydrochloric acid causes violent reactions due to differing chemical behavior. The CAS number prevents such mistakes.
In my experience working in a university chemistry lab, a graduate student once mislabeled a bottle as "HCl 1M" but used a solution of nitric acid. The label lacked the CAS number. When the student attempted to titrate a sample, the reaction produced toxic nitrogen oxides. The incident was traced to the absence of a proper identifier. After that, all bottles were required to display the CAS number, including 7647-01-0 for hydrochloric acid.
Unlike product codes or batch numbers, the CAS number 7647-01-0 is not a secret or proprietary code. It is publicly available through the CAS Registry database, accessible via the official website. Anyone can search for "7647-01-0" and retrieve detailed information, including synonyms, physical properties, and regulatory status.
The number is not assigned based on chemical class. Hydrochloric acid was registered in 1957. The number reflects historical assignment, not structural logic. The same applies to thousands of other chemicals. The system is designed for consistency, not predictability.