Browse Questions

Which one of the following cation will give a blue coloured ash when a piece of filter paper dipped in a solution containing its salt and $Co(NO_3)_2$ is burned?

(a) $Cu^{2+}$
(b) $Mg^{2+}$
(c) $Al^{3+}$
(d) $Zn^{2+}$

Answer: $Al^{3+}$

The filter paper ash test is substitute for cobalt nitrate charcoal cavity test. Double oxide $Al_3O_3.CaO$ formed is blue in colour.