Why Does Potassium Iodide Solution Conduct Electricity?

Potassium iodide dissociates into cations and anions when it’s dissolved in water, allowing electrons to flow freely through the solution. However, like other ionic compounds, it doesn’t conduct electricity when in a dry crystal form.

Read on to find out more about potassium iodide and why it’s conductive in an aqueous solution.

What is Potassium Iodide?

Potassium iodide is a simple inorganic ionic compound that’s composed of a positively-charged potassium and a negatively-charged iodine. It’s solid at room temperature and has a crystalline structure similar to table salt or sodium chloride. You can read more about this in our article ‘What is potassium iodide?’.

Potassium iodide is mainly used to treat hyperthyroidism and as a dietary supplement for people with an iodine deficiency. It’s also used to protect the thyroid gland against radiation and as an expectorant for treating asthma and other chronic respiratory conditions. Potassium iodide is mainly used to treat hyperthyroidism

Aside from its medical uses, potassium iodide has several industrial and commercial applications. For example, it’s used as a precursor compound in the manufacture of silver iodide, which is important in photography and printing. Potassium iodide also plays a crucial role in the synthesis of organic compounds, mainly aryl iodides. 

How to Prepare Potassium Iodide Solution

There are several ways to prepare potassium iodide, including from the reaction of a concentrated aqueous solution of potassium hydroxide and elemental iodine.

The steps in preparing potassium iodide are as follows:

  • Step 1: Potassium hydroxide is dissolved in water until it becomes a concentrated solution. This produces an exothermic reaction as the ions dissociate.
  • Step 2: Elemental iodine is added while the solution is hot. The solution may be subjected to external heat to maintain the ideal temperature and will become yellowish until all the iodine has been used up.
  • Step 3: Precipitates of potassium iodate (KIO3) will begin to form and settle at the bottom of the solution.
  • Step 4: The precipitates are separated from the solution through a filtration process after the solution has cooled down.
  • Step 5: The potassium iodide solution is then boiled down until just the potassium iodide crystals remain.

What is Electrical Conductivity in Chemistry?

Electrical conductivity in chemistry is simply a substance’s ability to allow the flow of electrons or electrical current through it. It’s related to the crystalline arrangement of the atoms of a substance and the way their electrons behave.

Electrical conductivity in chemistry is a substance’s ability to allow the an electrical current to flow through it

In metals, for example, atoms are arranged in regular patterns and electrons are delocalised. This means the electrons are not bound to a particular atom, allowing current to flow if there is an electric potential.

In aqueous ionic solutions, the charged ions (cations and anions) also allow the free flow of electrons. Potassium iodide solution is ionic, making it electrically conductive. However, when in a solid dry form, the compound does not conduct electricity. It can also conduct electricity when molten, but this is due to the potassium ions rather than the iodine ions.

Electrical conductivity is denoted by the Greek letter σ (sigma) and it’s measured in the SI units of siemens per metre (S/m). Electrical conductivity is the reciprocal of resistivity. You can therefore calculate the conductivity of a substance by measuring its resistivity. Typically, as the concentration of an ionic compound increases in a solution, its conductivity increases too.

Electrical conductivity is also affected by temperature. In metals, for instance, conductivity gradually increases as the temperature decreases. At a certain critical temperature level, the resistance of superconductors becomes zero, which makes them highly conductive.

How to Test Whether Potassium Iodide Solution Can Conduct Electricity

There are several ways to test the conductivity of a solution of potassium iodide. One of the simplest and easiest ways is to do an electrolysis test. 

To perform an electrolysis test, simply immerse two electrodes that are connected to a battery into the solution without touching each other. If bubbles form on the electrodes, then the solution is electrically conductive. These bubbles are oxygen and hydrogen gases liberated from the water.

The oxygen gas is generated via the anode or positively-charged electrode, while the hydrogen gas is generated via the cathode or negatively-charged electrode. See the schematic illustration below.

A schematic illustration of electrolytic production of hydrogen gas

You can also connect an LED or a small DC bulb to the circuit. An electrically conductive solution will act as a switch and close the circuit. The intensity of light produced is directly proportional to the conductivity of the solution and the distance between the electrodes. If you want a more accurate and precise measurement, you may also connect a voltmeter or an ohmmeter.

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