Ionic compounds exist in solid crystalline structure, held together by electrostatic forces between the oppositely charged ions. When dissolved in water, this structure breaks and positive and negatively charged ions are free to move within the liquid. Electrons from one electrode of the power supply are then carried by positively charged ions and transported to the oppositely charge electrode, hence, completing the electric circuit. More concentrated the ionic solution, more number of ions will be present and it becomes easier to conduct electricity.
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Some ionic compounds have such strong electrostatic forces between their ions that even when dissolved in water, they recombine and only few ions are left mobile in the solution. Such solutions have lesser capacity to transport electrons and are said to be weak electrolytes. Diluted solution of ionic compounds form weak electrolytes, as they give away fewer number of moveable ions for conduction purpose.
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