# Liquid Lights (DD-073)

> A liquid's electrical conductivity depends on how many ions it holds and how fast they move. Perfectly pure water isn't ion-free: it splits slightly into hydrogen and hydroxide ions, about 10⁻⁷ mol/L of each at 25 °C, which gives a theoretical conductivity of 0.055 µS/cm. Water left open to air absorbs carbon dioxide, which raises that to about 1 µS/cm. Strong electrolytes such as table salt, hydrochloric acid and sodium hydroxide split completely into ions and conduct well. Weak ones such as acetic acid and ammonia split only partly and conduct far less. Seawater conducts about a million times better than ultrapure water.

- Department: Science (also Tech)
- First published: 2026-02-16
- Last updated: 2026-02-16
- Permalink: https://detailenjoyer.com/case/liquid-lights/
- Author: Marcus Easterling (DetailEnjoyer), The Detail Department

## Quick facts

- **DD-073-F01**: Perfectly pure water still conducts slightly (0.055 µS/cm at 25 °C), because a tiny fraction of its molecules split into ions. _(Write-up · Exhibit B (Pure water isn't ion-free))_
- **DD-073-F02**: Weak acids such as acetic acid conduct far less than strong acids such as hydrochloric acid at the same concentration. _(Write-up · Exhibit D (Strong vs. weak))_

## Write-up

Why salt water conducts and pure water barely does. It's the dissolved ions that carry the current.

1. **Ions carry the current**: In water, salts, acids and bases split into positive and negative ions, and those ions carry the electric current. Conductivity rises with the number of ions and how fast they move.
2. **Pure water isn't ion-free**: Pure water splits slightly into hydrogen and hydroxide ions, about 10⁻⁷ mol/L of each at 25 °C. That gives a theoretical conductivity of 0.055 µS/cm.
3. **Air changes it**: Water exposed to air absorbs carbon dioxide, which raises its conductivity by a factor of 10 to 30, to roughly 0.8–1.2 µS/cm.
4. **Strong vs. weak**: Strong electrolytes such as hydrochloric acid and sodium hydroxide split completely into ions. Weak ones such as acetic acid and ammonia split only partly. At 1% by mass, hydrochloric acid conducts about 93 mS/cm and acetic acid about 0.6 mS/cm.
5. **Fast ions**: Hydrogen and hydroxide ions are the fastest movers in water. Their limiting ionic conductivities are about 350 and 199, compared with 50 for sodium (S·cm²/mol at 25 °C).
6. **A million-fold range**: Seawater conducts about 0.053 S/cm at 25 °C, roughly a million times more than ultrapure water.

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## Reel vs. record

- **Nuance**: pure water doesn't completely 'lack free ions'. It splits slightly into H⁺ and OH⁻ (about 10⁻⁷ mol/L each at 25 °C), giving 0.055 µS/cm. Distilled water left in air picks up CO₂ and reaches about 1 µS/cm. [Metrohm; NIST; CHIMIA]
- **Nuance**: not every acid or base 'conducts well'. Strong ones split fully into ions, but weak ones like acetic acid and ammonia split only partly. At 1%, acetic acid conducts about 0.6 mS/cm versus about 93 mS/cm for hydrochloric acid. [Metrohm; CRC Handbook]
- **Context on mobility**: H⁺ and OH⁻ move far faster than other ions (about 350 and 199 versus 50 for Na⁺). That's a big part of why strong acids and bases conduct so well. [Metrohm]
- **Context on scale**: seawater conducts about 0.053 S/cm at 25 °C, roughly a million times more than ultrapure water. [CHIMIA]
- **Confirmed**: conductivity depends on the presence and mobility of ions; dissolved salts make water conductive. Conductivity also changes with temperature, by about 5.8% per °C for pure water. [Metrohm]

## Video: Liquid Lights: Why Salt Water Conducts and Pure Water Barely Does

- Duration: 20.6 s · Published: 2026-02-16
- File: https://detailenjoyer.com/assets/videos/DU1fwKQkon5.mp4

### Transcript

DID YOU KNOW? Fluid-based conductivity refers to the ability of a liquid to conduct electricity, which depends on the presence and mobility of charged particles within it. In most cases, pure liquids like distilled water conduct very poorly because they lack free ions, while fluids containing dissolved salts, acids, or bases conduct well because they contain mobile positive and negative ions. NOW YOU KNOW!

## Questions & answers

**Q: What carries current through salt water?**  
A: Salts split into positive and negative ions. _(Source: Write-up · Exhibit A (Ions carry the current) · Conductometry monograph (Metrohm))_

**Q: Theoretical conductivity of pure water at 25 °C?**  
A: It comes from water splitting slightly into ions. _(Source: Write-up · Exhibit B (Pure water isn't ion-free) · Conductometry monograph (Metrohm); Traceable standards for electrolytic conductivity measurements (CHIMIA, 2009))_

**Q: Why does distilled water left in air conduct more?**  
A: CO₂ raises it 10 to 30 times. _(Source: Write-up · Exhibit C (Air changes it) · Low electrolytic conductivity standards (Journal of Research of NIST, via PMC))_

**Q: Which is a weak electrolyte?**  
A: Acetic acid splits only partly into ions. _(Source: Write-up · Exhibit D (Strong vs. weak) · Conductometry monograph (Metrohm); Electrical conductivity of aqueous solutions (CRC Handbook of Chemistry and Physics, 91st ed.))_

**Q: Roughly how much better does seawater conduct than ultrapure water?**  
A: That's about 0.053 S/cm versus 0.055 µS/cm. _(Source: Write-up · Exhibit F (A million-fold range) · Traceable standards for electrolytic conductivity measurements (CHIMIA, 2009))_

## Sources

- [Conductometry monograph (Metrohm)](https://www.metrohm.com/content/dam/metrohm/shared/documents/monographs/81095021EN.pdf)
- [Low electrolytic conductivity standards (Journal of Research of NIST, via PMC)](https://pmc.ncbi.nlm.nih.gov/articles/PMC4887229/)
- [Traceable standards for electrolytic conductivity measurements (CHIMIA, 2009)](https://www.chimia.ch/chimia/article/download/2009_647/4020/14705)
- [Electrical conductivity of aqueous solutions (CRC Handbook of Chemistry and Physics, 91st ed.)](https://diverdi.colostate.edu/all_courses/CRC%20reference%20data/electrical%20conductivity%20of%20aqueous%20solutions.pdf)

## Cite this case file

Easterling, Marcus. "Liquid Lights." The Detail Department (DetailEnjoyer), case file DD-073, last updated Feb 16, 2026. https://detailenjoyer.com/case/liquid-lights/