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  • In qualitative analysis when {H}_{2} {S} is passed through an aqueous solution of salt acidified with dil.{HCl}, a black precipitate is obtained. On boiling the precipitate with dil.{HNO}_{3}, it forms a solution of blue colour.

In qualitative analysis when \text {H}_{2}\text {S} is passed through an aqueous solution of salt acidified with dil.\text {HCl}, a black precipitate is obtained. On boiling the precipitate with dil. \text {HNO}_{3}, it forms a solution of blue colour. Addition of excess of aqueous solution of ammonia to this solution gives _________.

(i) a deep blue precipitate of \text {Cu(OH)}_{2}

(ii) a deep blue solution of [Cu(NH_{3})_{4}]^{2+}

(iii) a deep blue solution of Cu(NO_{3})_{2}

(iv) a deep blue solution of Cu(OH)_{2}.Cu(NO_{3})_{2}

Answers (3)

The answer is the option (ii). Black precipitate of copper sulphide is formed on passing H_{2}S through acidified solution of salt. On boiling with dilute HNO_{3}, the precipitate gives blue colour of copper nitrate. On addition of excess aqueous solution of ammonia, deep blue coloured compound is found. The reactions involved are:

Cu^{2+}+H_{2}S\rightarrow CuS (black)+2H^{+}

                                                                    CuS+dil.HNO_{3}\rightarrow Cu\left ( NO_{3} \right )_{2}

                                              Cu\left ( NO_{3} \right )_{2}+4NH_{3}\rightarrow \left [ Cu\left ( NH_{3} \right )_{4} \right ]^{2+}(Deep\; blue)

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The answer is the option (ii). Black precipitate of copper sulphide is formed on passing H_{2}S through acidified solution of salt. On boiling with dilute HNO_{3}, the precipitate gives blue colour of copper nitrate. On addition of excess aqueous solution of ammonia, deep blue coloured compound is found. The reactions involved are:

 

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infoexpert23

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The answer is the option (ii). Black precipitate of copper sulphide is formed on passing H_{2}S through acidified solution of salt. On boiling with dilute HNO_{3}, the precipitate gives blue colour of copper nitrate. On addition of excess aqueous solution of ammonia, deep blue coloured compound is found. The reactions involved are:

Cu^{2+}+H_{2}S\rightarrow CuS (black)+2H^{+}

                                                               CuS+dil.HNO_{3}\rightarrow Cu(NO_{3})_{2}

                                    Cu(NO_{3})_{2}+4NH_{3}\rightarrow [Cu(NH_{3})_{4}]^{2+}(Deep\; blue)

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