Question

Several transition metals form complexions with ammoniamuch like copper. Zincis one such metal(forms Zn(NH3)42+).Why does its presence in large amountsin pennies (95+ %) not interfere in the determination of copper?

Answer 1

A penny is made of a core of zinc (95%) and the core is covered with layers of copper (5%). Both copper and zinc forms complex ions. Copper ammonia complex is pale bluish in color and it can be identified. The quantity of copper can be identified by measuring the absorption of the complex ion in a spectrometer. Zinc also form the ammonium complex ion. However, the complex does not interfere in the determination of copper because its wavelengths of absorption are different from the complex ion of copper.