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Surface Chemistry — Chemistry STD 12 Science — Question

Gujarat BoardEnglish MediumSTD 12 ScienceChemistrySurface Chemistry3 Marks
Question
$SnO_2$ forms a positively charged colloidal sol in acidic medium and a negatively charged sol in the basic medium. Why? Explain.
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Answer

$SnO_2$ is amphoteric in nature. It reacts with acids such as $HCl,$ to form $SnCl_4$ in the solution.
The common $Sn^{4+}$ ions are adsorbed on the surface of $SnO_2$ particles to give a positively charged colloidal sol. $\text{SnO}_2+4\text{HCl}\rightarrow\text{SnCl}_4+2\text{H}_2\text{O}$$\text{SnO}_2 +\text{Sn}^{4+}\xrightarrow{\ \ \ \ \ \ \ \ \ \ \ \ \ \ }(\text{SnO}_2):\text{Sn}^{4+}\\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ ^\text{Positively charged sol}$
$SnO_2$ is amphoteric in nature. It reacts with acids such as $HCl,$ to form $SnCl_4$ in the solution.
The common $Sn_4+$ ions are adsorbed on the surface of $SnO_2$ particles to give a positively charged colloidal sol. $\text{SnO}_2+2\text{NaOH}\xrightarrow{\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ }\text{Na}_2\text{SnO}_3+\text{H}_2\text{O}\\\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ ^\text{Sodium stannate}$ $\text{SnO}_2+\text{SnO}^{2-}_3\xrightarrow{\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ }(\text{SnO}_2):\text{SnO}^{2-}_3\\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ ^\text{Negatively charged sol}$

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