Salts and their reactions : a text-book of practical chemistry / by Leonard Dobbin and Hugh Marshall.

  • Doddin, Leonard, 1858-
Date:
1912
Catalogue details

Licence: In copyright

Credit: Salts and their reactions : a text-book of practical chemistry / by Leonard Dobbin and Hugh Marshall. Source: Wellcome Collection.

    47/222 (page 33)
    case. Some sulphides, insoluble in water, dissolve with great readiness in dilute acetic acid ; manganous sulphide is a good example. Others, such as zinc sulphide, dissolve easily in strong acids, such as hydrochloric acid, but scarcely at all in acetic acid; others again, such as lead sulphide, are decom- posed somewhat readily by strong acids, but yet can be com- pletely precipitated by hydrogen sulphide in excess, even in presence of such acids, provided the solution is moderately dilute and the temperature low ; a few, like arsenious sulphide, are scarcely attacked even by strong acids. The explanation of these differences is to be sought in the different degrees of solubility of the sulphides themselves in water. The balance existing between any solid sulphide and, say, hydrochloric acid may be represented thus ;— H^S MS MS M'.: + S (Solid) (Dissolved) ^ _|_ 2 cr + 2 H- ^ 2 HCl ' • MClg Hydrochloric acid and metallic chlorides being all ionised to a much greater extent than hydrogen sulphide is, the factor which will decide whether or not the sulphide dissolves in the acid must be the relative extent to which the metallic sulphide and the hydrogen sulphide are ionised in the solution. If the metallic sulphide is so very sparingly soluble that its saturated aqueous solution contains a much lower concentration of S ions than a solution of hydrogen sulphide does, hydrogen sulphide will precipitate that sulphide from an acid solution of an appropriate salt. In such a case, however, the addition of a large quantity of free acid may, by greatly increasing the concentration of H' ions, so far diminish the ionisation of the hydrogen sulphide (see p. 26) that the latter becomes the least ionised product, whereupon the sulphide will begin to dissolve up. The diagram given above is not complete, because in many cases the balance H2S H2S (Dissolved) (Gas) is of importance (especially at high temperatures), and in some cases also the balance MCI2 ^ MCI2 (Solid) (Dissolved) may come into play (in the case of lead sulphide, for example). C