B. Detection of commonly occurring acids when not more than one is present in any group*. I. Test for nitric acid by ferrous sulphate test (8. Part I. Chap. VII. Exp. 4). II. GROUP I. To original solid (if liquid is given evaporate to dryness on steam-bath) add concentrated sul phuric acid: If no reaction occurs with sulphuric acid in the cold, then To prepare the solution for the remaining groups, add a large excess of solid sodium carbonate to the original liquid, or if original is a solid add Na,CO, and a little watert; boil for 5-10 mins., filter off the pp. of metallic carbonates, just acidify the filtrate by adding dilute nitric acid, boil, and filter again if necessary. The solution should now be neutral; if not, make it so by very cautious addition of very dilute ammonia. III. GROUP II. To a portion of the neutral liquid add barium nitrate solution; if a white pp. forms add to it dilute nitric acid: * Chromic, arsenic, and arsenious, acids, if present, will have been detected in testing for metals. + If the addition of excess of Na,CO,Aq to a little of the original liquid produces no pp. the treatment with Na,CO, described above is unnecessary; the liquid must however be neutral before examining for Grs. II. and III. Treatment with Na,CO, removes metals, that would interfere with the subsequent tests for acids, by pptg. them as carbonates; the filtrate contains sodium salts of the acids. |