Question

On reaction of sodium hydroxide with copper ions gives the colored precipitate. Tell the colour.
A.Blue/ Turquoise
B.Pink
C.Red
D.White

Answer 1

Hint:Copper (II) ions or cupric ions, when reacted with sodium hydroxide, forms copper (II) hydroxide which being insoluble in water settles down as a precipitate. To answer this question, you must recall the color shown by copper hydroxide salt.

Complete answer:
The reaction between sodium hydroxide and copper ions proceeds as,
$C{u}^{2+}+2O{H}^{-}\to Cu{\left(OH\right)}_2$
Copper hydroxide is a widely used reagent in laboratories. Using our practical knowledge and memory, we can determine the colour of copper hydroxide. But first, we need to learn about the salt.
Copper hydroxide or cupric hydroxide is a weak basic oxide of copper and is represented by the chemical formula $Cu{\left(OH\right)}_2$. It is used commonly as a reagent in various chemical reactions in laboratories as well as industrially. It is produced using a similar reaction as given in the question. It involves the reaction between sodium hydroxide and copper sulphate solution which gives copper hydroxide and sodium sulphate as the products.
Copper hydroxide is pale greenish blue (turquoise) or blue coloured salt.

Hence, the correct answer is A.

Note:
The copper ion in the center of the molecule has a square pyramidal shape. The hydroxyl ligands which are present in the plane of the structure are bridging ligands. The structure of the molecule is determined using the method of X- ray crystallography. Copper hydroxide being a weak base, has a very specialized role in synthesis of organic compounds. The compound is widely used in the chemical industries for the synthesis of aryl amines. Copper hydroxide is also used as a pigment in paints and ceramics.