Water as an electricity conductor and self ionization

So H2O cannot conduct electricity because it doesn’t have any free ions. on the other hand H3O+ and OH- can. So in real life water do conduct electricity because of water self ionization. But in a theoretical question, the answer might be that water is an insulator. How Should we approach this?


I find that exam questions specify if we are dealing with a solution of normal water (H2O that can self-ionize and conduct electricity), or if we are dealing with PURE or distilled water that acts as an insulator (solution of only stable H2O molecules)
Often we need to rely on key terms to solve

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As you rightly mentioned (as well as Juliette above), pure water (H2O) is a poor conductor of electricity because it doesn’t have free ions. However, this doesn’t mean it’s an absolute insulator. It is, more accurately, a very poor conductor under normal conditions.

Water can conduct electricity when it contains ions, and this happens in two main ways:

  1. Impurities: Ordinary tap water, seawater, or even rainwater contain a lot of impurities, such as salts and minerals. These impurities often break down into ions when dissolved in water, thereby enhancing water’s electrical conductivity.
  2. Self-ionization: Water can also ionize itself, albeit to a very small degree. This process, known as auto-ionization or self-ionization, involves two water molecules reacting to form a hydronium ion (H3O+) and a hydroxide ion (OH-). However, the concentration of these ions in pure water is extremely low (around 10^-7 M at 25 °C), so this doesn’t significantly contribute to conductivity under normal conditions.

In response to your other question about how to approach this in a theoretical question, it’s crucial to be clear about the conditions. If the question is about pure water (H2O), then the correct response would be that it’s a poor conductor or a near-insulator. However, if the question doesn’t specify the type of water, then you could argue that most water we encounter in the real world conducts electricity due to ions from impurities or self-ionization. Note that on the IMAT they usually mention if the water is pure or if it contains ions as solutes, which will change the answer.

Remember, the context and conditions matter a lot on the IMAT, so keep an eye on every detail they give about the system described.

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