Question

Two additional compounds were studied: NO2(OH) dissolved in water and produced an acidic solution, and Ni(OH)2 dissolved only in an acidic solution. What type of compounds were these?

A. Both were oxyacids.

B. Both were bases.

C. NO2(OH) was a base and Ni(OH)2 was an oxyacid.

D. NO2(OH) was an oxyacid and Ni(OH)2 was a base.

This is the solution:

This is a General Chemistry question that falls under the content category “Unique nature of water and its solutions.” The answer to this question is D. The first substance is nitric acid, HNO3. Since this substance dissolves to generate an acidic solution, the bond between O and H in the structural formula NO2OH breaks when the substance dissolves, making it an oxyacid. The latter substance, Ni(OH)2, is apparently insoluble in neutral water, but will dissolve if the solution is acidic. This behavior is typical of substances that feature basic anions. The bond between Ni and O is the one that breaks when Ni(OH)2 dissolves. The hydroxide ion that is produced quickly reacts with protons in solution and cannot react again with Ni2+ to form a precipitate. This question requires Knowledge of Scientific Concepts and Principles to arrive at the answer.

This is a gap in my knowledge but I don't understand why we know Ni (OH)2 is a base because it dissolves in an acidic solution and not water. Why doesn't the base dissolve in water?

Answer 1

Ni(OH)2 is base but this is not strong base this is very weak base and this cannot gives OH- after dissolving in H2​​​O . this is only dissolve in acidic solition.