Ho Shing 發問於 科學及數學化學 · 1 十年前

The electrical conductivity of pure water

We know that the substances which contain mobile ions,is electrical conductive.Although pure water contain mobile ions(H+ and OH-) , it does not conduct electricity.Explaine that.

1 個解答

  • 1 十年前

    Water molecules only slightly ionize in water, i.e. only a very small proportion of water molecules ionize. My teacher told me that approximately, if there are 1000 water molecules, only one ionizes. The concentration of H+ and OH- is so small that water cannot conduct electricity well. However, I believe that water conducts electricity at high voltage. Everything conducts electricity at high voltage, right? :)

    I am still a F.5 student, so I don't know the explanation in detail. I have find some information from Wikipedia for you. Hope they are helpful.

    I think the article below is the most helpful, especially the first paragraph.

    From Wikipedia:

    (http://en.wikipedia.org/wiki/Electrolysis_of_water Electrolyte selection)

    If electrolysis occurs in pure water, H+ cations will accumulate at the anode and OH− anions will accumulate at the cathode. This can be verified by adding a pH indicator to the water: the water near the anode is acidic while the water near the cathode is basic. These charged ions will repel the further flow of electricity until they have diffused away, a slow process. This is why pure water conducts electricity poorly and why electrolysis of pure water proceeds slowly.

    If a water-soluble electrolyte is added, the conductivity of the water rises considerably. The electrolyte disassociates into cations and anions; the anions rush towards the anode and neutralize the buildup of positively charged H+ there; similarly, the cations rush towards the cathode and neutralize the buildup of negatively charged OH− there. This allows the continued flow of electricity.

    There are also some statistic for electrolysis of pure water.

    From Wikipedia:

    (http://en.wikipedia.org/wiki/Water_%28molecule%29 Electrical Conductivity)

    In pure water, sensitive equipment can detect a very slight electrical conductivity of 0.055 µS/cm at 25 °C. Water can also be electrolyzed into oxygen and hydrogen gases but in the absence of dissolved ions this is a very slow process, as very little current is conducted.

    資料來源: Wikipedia