Question

Repor A) Reactions with selected reagents On the basis ofyour observations, group the elements tested into families. Indicate the for your groupings. 2 Do your groupings agree with those in the periodic table? Explain. memhers of a given chemical family have in common. Reaction with Ag. No, formula of precipitate, if any of formula of cation precipitate i - Neppt 2P+ ppt Li, NO Na", NO Sr, NO Pt S NH, NO nu fr

Answer 1

The following combinations give precipitates.

i) Ba²⁺, NO₃^- and NH₄⁺, CO₃^2-.

ii) Ca²⁺, NO₃^- and NH₄⁺, CO₃^2-.

iii) Sr²⁺, NO₃^- and NH₄⁺, CO₃^2-.

iv) Ba²⁺, NO₃^- and NH₄⁺, PO₄^3-.

v) Ca²⁺, NO₃^- and NH₄⁺, PO₄^3-.

vi) Sr²⁺, NO₃^- and NH₄⁺, PO₄^3-.

vii) NH₄⁺, Cl^- and Ag⁺, NO₃^-.

viii) NH₄⁺, I^- and Ag⁺, NO₃^-.

ix) NH₄⁺, Br^- and Ag⁺, NO₃^-.

A1. The elements tested above can be grouped into two families

(i) Ba²⁺, Ca²⁺ and Sr²⁺ give precipitates with both CO₃^2- and PO₄^3-.

(ii) Cl^-, I^- and Br^- give precipitates with Ag⁺.

The counterions are not mentioned above since the counter ions are the same for all the salts tested in (i) and (ii).

A2. The groupings definitely agree with the periodic table. Ca²⁺, Ba²⁺ and Sr²⁺ belong to group IIA of the periodic table and are alkaline earth metals. All alkaline earth metals form insoluble carbonates and phosphates.

Similarly, Cl^-, Br^- and I^- are derived from elements belonging to the same family in the periodic table – group 17 and are known as halogens. All the elements are electronegative non-metals.