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Liquid Lights

Short answer: 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.

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What should you know about Liquid Lights?

Quick facts. Each one stands alone and has a stable ID you can cite.

  1. Perfectly pure water still conducts slightly (0.055 µS/cm at 25 °C), because a tiny fraction of its molecules split into ions.

    DD-073-F01 · Write-up · Exhibit B (Pure water isn't ion-free)

  2. Weak acids such as acetic acid conduct far less than strong acids such as hydrochloric acid at the same concentration.

    DD-073-F02 · Write-up · Exhibit D (Strong vs. weak)

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

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!

Burned-in captions, read frame by frame (see transcript.md) · 20.6s Reel ·

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The write-up

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

  1. Exhibit A

    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. Exhibit B

    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. Exhibit C

    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. Exhibit D

    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. Exhibit E

    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. Exhibit F

    A million-fold range

    Seawater conducts about 0.053 S/cm at 25 °C, roughly a million times more than ultrapure water.

Questions people ask about Liquid Lights

What carries current through salt water?

Salts split into positive and negative ions.

Source: Write-up · Exhibit A (Ions carry the current) · Conductometry monograph (Metrohm)

Theoretical conductivity of pure water at 25 °C?

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)

Why does distilled water left in air conduct more?

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)

Which is a weak electrolyte?

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.)

Roughly how much better does seawater conduct than ultrapure water?

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)

Test Your Knowledge

All quizzes →

5 questions, all from this case file. Answers are revealed instantly.

  1. What carries current through salt water?

    1. Free electrons
    2. Dissolved ions
    3. Photons
    4. Water molecules
    Show the answer

    Answer: B. Dissolved ions Salts split into positive and negative ions. Source: Write-up · Exhibit A (Ions carry the current) · Conductometry monograph (Metrohm)

  2. Theoretical conductivity of pure water at 25 °C?

    1. Exactly zero
    2. 0.055 µS/cm
    3. 1 mS/cm
    4. 0.053 S/cm
    Show the answer

    Answer: B. 0.055 µS/cm 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)

  3. Why does distilled water left in air conduct more?

    1. It absorbs carbon dioxide
    2. It cools down
    3. It evaporates
    4. Light hits it
    Show the answer

    Answer: A. It absorbs carbon dioxide 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)

  4. Which is a weak electrolyte?

    1. Hydrochloric acid
    2. Sodium hydroxide
    3. Acetic acid
    4. Table salt
    Show the answer

    Answer: C. Acetic acid 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.)

  5. Roughly how much better does seawater conduct than ultrapure water?

    1. 10 times
    2. 1,000 times
    3. A million times
    4. A billion times
    Show the answer

    Answer: C. A million times 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)

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/

Permalink: https://detailenjoyer.com/case/liquid-lights/ · Last updated

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Cite a single fact by its ID, for example DD-073-F01 → https://detailenjoyer.com/case/liquid-lights/#DD-073-F01

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