Question

What should I start with Cations or Anions? And why good answer please!

Answer 1

The five groups of cations and the characteristics of these groups are as follows:

Group 1 Cations of this group form precipitates with dilute hydrochloric acid. Ions of this group are lead(II), mercury(I), and silver(I).

Group 2 The cations of this group do not react with hydrochloric acid, but form precipitates with hydrogen sulphide in dilute mineral acid medium. Ions of this group are mercury(II), copper(II), bismuth(III), cadmium (II), tin(II), tin(IV), arsenic(III), arsenic(V), antimony(III), and antimony(V). The first four form the sub-group 2/a and the last six the sub-group 2/b. While sulphides of cations in Group 2/a are insoluble in ammonium polysulphide, those of cations in Group 2/b are soluble.

Group 3 Cations of this group do not react either with dilute hydrochloric acid, or with hydrogen sulphide in dilute mineral acid medium. However they form precipitates with ammonium sulphide in neutral or ammoniacal medium. Cations of this group are iron(II), iron(III), cobalt(II), nickel(II), manganese(II), chromium(III), aluminium(III), and zinc(II).

Group 4 Cations of this group do not react with the reagents of Groups 1, 2, and 3. They form precipitates with ammonium carbonate in the presence of ammonium chloride in neutral medium. Cations of this group are calcium(II), strontium(II), and barium(II).

Group 5 Common cations, which do not react with reagents of the previous groups, form the last group of cations, which includes magnesium(II), lithium(I), sodium(I), potassium(I), and ammonium(I) ions.

The following scheme of classification of anions has been found to work well in practice; anions are divided into four groups on the basis of their reactions with dilute hydrochloric acid and of the differences of solubilities of their barium and silver salts.

The four groups of anions and the characteristics of these groups are as follows:

Group 1 Visible change, gas evolution and/or formation of a precipitate, with dilute hydrochloric acid. Ions of this group are carbonate, silicate, sulphide, sulphite, and thiosulphate.

Group 2 The anions of this group do not react with hydrochloric acid, but form precipitates with barium ions in neutral medium. Ions of this group are sulphate, phosphate, fluoride, and borate.

Group 3 Anions of this group do not react either with dilute hydrochloric acid, or with barium ions in neutral medium. However, they form precipitates with silver ions in dilute nitric acid medium. Anions of this group are chloride, bromide, iodide, and thiocyanate.

Group 4 Common anions, which do not react with reagents of the previous groups, form the last group of anions, which includes nitrite, nitrate and chlorate ions.