Which ion in excess naoh does not form soluble complex?
Answers
copper and various other transition metals in solution tend to form insoluble hydroxides. This tendency has been used for removing such metals from industrial wastewaters. In that context, I believe the expression “in excess NaOH” means - with sufficient NaOH to raise the pH substantially above neutral. The reason an abundance of NaOH would be required for this purpose is that solutions containing high concentrations of metals such as copper are frequently quite acidic. For example, copper removed from electronic components is often encountered as acidic copper chloride. If only a little bit of NaOH were added, the pH would remain low and the copper would remain soluble.
As a side note, copper chloride solution can be sprayed on concrete to “acid stain” the concrete. The copper reacts with carbonate and silicates in the concrete to form greenish copper salts. Just as copper oxide is not soluble, neither is copper carbonate or copper silicate. But, solubility is a relative thing. Even if a compound is referred to as insoluble, that does not mean NONE of it dissolves. When we make environmental contamination measurements, just about everything is at least a little bit soluble.
copper and various other transition metals in solution tend to form insoluble hydroxides. This tendency has been used for removing such metals from industrial wastewaters. In that context, I believe the expression “in excess NaOH” means - with sufficient NaOH to raise the pH substantially above neutral. The reason an abundance of NaOH would be required for this purpose is that solutions containing high concentrations of metals such as copper are frequently quite acidic. For example, copper removed from electronic components is often encountered as acidic copper chloride. If only a little bit of NaOH were added, the pH would remain low and the copper would remain soluble.
As a side note, copper chloride solution can be sprayed on concrete to “acid stain” the concrete. The copper reacts with carbonate and silicates in the concrete to form greenish copper salts. Just as copper oxide is not soluble, neither is copper carbonate or copper silicate. But, solubility is a relative thing. Even if a compound is referred to as insoluble, that does not mean NONE of it dissolves. When we make environmental contamination measurements, just about everything is at least a little bit soluble.
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