If FeCl3 is added to excess of hot water, a postively charged sol of hydrated ferric oxide is formed due to adsorption of Fe3+ ions. However, when ferric chloride is added to NaOH, a negatively charged sol is obtained with adsorption of OH- ions. Why is there such a difference? Explain in detail.
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A negatively charged sol of hydrated ferric oxide is formed when ferric chloride is added to NaOH solution as follows:
FeCl₃+ 2NaOH → Fe(OH)₃ + 3NaCl.
The negatively charged solution is obtained because of the preferential adsorption of the OH− ions which form an electrical double layer.
As for the addition of FeCl₃ to hot water, a positively charged solution is formed due to adsorption of Fe³⁺.
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