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Question
A colloid is formed by adding \[\ce{FeCl3}\] in excess of hot water. What will happen if excess sodium chloride is added to this colloid?
Solution
\[\ce{FeCl3}\] when added into hot water, it forms hydrated ferric oxide, which is a positively charged sol due to absorption of \[\ce{Fe^{3+}}\] ions. On adding \[\ce{NaCl}\] the negatively charged chloride ions neutralize the positive charge of the solution and coagulation of the sol takes place.
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