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| Electrolytes and Non-electrolytes |
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| An ionic or electrovalent compound that conducts electricity in molten (fused) or aqueous (solution) state can be classified as an electrolyte. However, if the compound is unable to ionise it does not conduct electricity it is called a non-electrolyte. In general, the extent to which an electrolyte can break up into ions categorises an electrolyte. This gives a measure of the degree of dissociation (a) of an electrolyte. Based on this degree the electrolytes can be classified as strong or weak electrolyte and non-electrolyte. |
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| Strong Electrolyte |
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| A strong electrolyte dissociates or ionises completely or almost completely to form free mobile ions in the solution or molten form. The more the availability of free mobile ions in an electrolyte, the greater is its capacity to carry or conduct current i.e. the stronger the electrolyte. The ability to conduct current can be observed by setting up a cell as shown in figure 4.4. The bulb glows brightly. |
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| For e.g., |
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 Sodium chloride even in crystalline form consists of ions. But the ions are not mobile. When melted or dissolved in water, it dissociates completely into free, mobile ions. |
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Pure sulphuric acid exists mostly in the form of molecules. But when mixed with water, it almost completely breaks up into free mobile ions. |
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| A weak electrolyte ionises or dissociates only partially to form free mobile ions. Most of the electrolyte remains as un-ionised molecules. For example in acetic acid, the number of its dissociated ions (the acetate and hydrogen ions) is less compared to the total amount of acetic acid molecules present. Similarly in ammonium hydroxide the number of its dissociated ions (the ammonium and hydroxyl ions) are less compared to the total amount of the molecules present. |
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| Thus both these compounds are weak electrolytes. |
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| When the number of mobile ions is less in an electrolyte, the lesser is its capacity to carry or conduct current i.e. the weaker is the electrolyte. This is observed by setting up the cell as shown in figure 4.5. The bulb glows less brightly. |
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| If one liter of a solution containing one molar mass of sulphuric acid, and one liter of a solution containing one molar mass of citric or acetic acid, are subjected to the same current, then: |
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The bulb glows brightly in the case of the sulphuric acid, showing it to be a strong electrolyte |
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The bulb glows dimly in the case of the citric or acetic acid, showing that it is a weak electrolyte. |
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| A non-electrolyte does not provide ions in a solution and therefore current does not flow through such solution. The bulb in the given set up does not glow (Fig.4.6). Some examples of non-electrolytes are: alcohol, carbon tetrachloride, carbon disulphide. |
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