Source: https://guthlabs.ai/docs/instruments/ph-poh-calculator/mechanism/

instrument mechanism / verified-clean

# pH / pOH Calculator mechanism

The inspectable method record for pH / pOH Calculator, kept separate from implementation and qualification.

Status: **VERIFIED_CLEAN**Lifecycle: **verified-clean**

## Model scope

The core arithmetic is correct for ideal dilute aqueous solutions at approximately 25 °C with concentrations expressed in mol/L. NEEDS_REVIEW is required because the specification leaves concentration units and the concentration-versus-activity convention implicit, and the fixed pH+pOH=14 relationship is temperature-dependent. The honest label appropriately mentions the 25 °C assumption but should also explicitly state the mol/L and ideal-solution assumptions.

- The formulas are standard under the stated 25 °C approximation, but pH and pOH are rigorously defined from activities rather than raw concentrations; using [H+] and [OH-] requires an ideal-dilute-solution assumption.

- pH+pOH=14 is valid only when pKw=14.000, approximately at 25 °C under the selected activity/concentration convention. It is not generally valid at other temperatures.

- The specification does not state the required units for [H+] and [OH-]. They must be supplied consistently, conventionally in mol/L, or the logarithms and Kw calculation are ambiguous.

## Units and conventions

- [H+] and [OH-] are aqueous concentrations in mol/L (M), not mmol/L or mol/m³.

- Kw=1.0×10^-14 has units of (mol/L)^2 under the concentration approximation.

- All calculations use base-10 logarithms.

- The solution is sufficiently dilute that activities can be approximated by concentrations.

- The default temperature is 25 °C; for other temperatures, a supplied Kw(T) must replace 1.0×10^-14 and pH+pOH=14 must be replaced by pH+pOH=pKw(T).

## Inspectable vector

One of 4 source-bound review vectors:

````
{
  "inputs": {
    "pH": "0.00"
  },
  "expected_outputs": {
    "pOH": "14.000000",
    "[H+]_mol_per_L": "1.000000×10^0",
    "[OH-]_mol_per_L": "1.000000×10^-14"
  },
  "working": "pOH = 14.000000 - pH = 14.000000 - 0.000000 = 14.000000.\n[H+] = 10^(-pH) = 10^0 = 1.000000 mol/L.\n[OH-] = Kw/[H+] = (1.000000×10^-14)/(1.000000) = 1.000000×10^-14 mol/L.\nThis is a boundary-like case: pH=0 is valid mathematically, but represents an idealized 1 mol/L hydrogen-ion concentration."
}
````

## Failure boundary

**BREAK_CLAIMED** · SELF_FLAGGED

The specification does not define validation or rejection behavior for zero or negative concentrations, although these inputs cause division by zero or logarithms outside the real domain. It also leaves concentration units implicit, allowing a 3-pH-unit discrepancy for the same displayed numeric input.

## Other records

[01**Overview**](<https://guthlabs.ai/docs/instruments/ph-poh-calculator/>)[03**Implementation**](<https://guthlabs.ai/docs/instruments/ph-poh-calculator/implementation/>)[04**Qualification**](<https://guthlabs.ai/docs/instruments/ph-poh-calculator/qualification/>)

## Sources and evidence

These pointers bind the page to evidence. They do not grant authority or collapse verification into deployment.

- `VERIFIED_LEDGER.json`

- `evidence-tranche6/tranche6-results.json`

- `BOUNDARY_HAZARD_CATALOG.json`