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Strontium, and Calcium.
(NH4)2CO3, and filter. Wash precipitate with hot H,O, dissolve in HCI, a precipitate after some time indicates Strontium, or a dilute Barium the solution in HCl add H2SO4, and boil to remove Ba and Sr. Filter. precipitate indicates Calcium.
III. Ba AND Ca PRESENT. precipitate with H2SO4. Add H,S04 to the HCl solution (diluted to prevent wash well.
precipitation of Calcium), and filter.
and evaporate to dryalcohol. Filter.
Confirm as above.
Dissolve the carbonates in C2H4O2, and precipitate the Ba with K CrO4. Filter. Precipitate the Sr and Ca by (NH4)2CO3, and proceed as in Method II. (Ba Absent, Ca Present).
Reactions of the Metals of the Potassium Group.
89. Metals whose solutions are unprecipitated by the preceding group reagents, but which have no common precipitant, and are therefore recognized by individual tests.
Magnesium, Potassium, Ammonium, Sodium. MAGNESIUM. Mg, c.w. 24.
1. Na,HPO4 produces, in presence of (NH)HO and NH4Cl, a crystalline white precipitate of MgNH,POJ. From dilute solutions the precipitation is slow, but
may be hastened by stirring with a glass rod. The precipitate is soluble in dilute mineral acids and in C2H402 but is almost insoluble in dilute solution of (NH)HO.
2. (NH4)HO in neutral solutions produces a partial precipitation of the hydrate Mg(HO),, but gives no precipitate in presence of NH4Cl, in which the hydrate is readily soluble.
3. H2SO4, H,SiFe, and C (NH)204 yield no precipitates.
4. Heated on charcoal in the blow-pipe flame, then moistened with CoCl, and re-heated, a pink mass is obtained.
90. POTASSIUM. K, c.w. 39ʻI.
1. PtCl4 produces a crystalline yellow precipitate of 2 KCl + PtCl,, except in dilute solutions, which are not precipitated. The precipitation is promoted by stirring, or by addition of alcohol.
2 Tartaric acid precipitates white crystalline hydro
gen potassium tartrate from strong and neutral solutions. The precipitation is promoted by stirring.
3. H,SiFe produces a white gelatinous precipitate of K,SiF6
4. Heated on platinum wire in the non-luminous flame, a violet coloration is produced, which when viewed through a piece of blue glass appears reddish violet.
91. AMMONIUM, NH4, C.W. 18.
1. PtCl, produces a crystalline yellow precipitate of -2 NH4Cl + PtClų, except in dilute solutions, which are not precipitated. The precipitate is insoluble in alcohol and ether, and when ignited leaves a residue of spongy platinum.
2. Tartaric acid produces, in strong solutions, a white precipitate of hydrogen ammonium tartrate, similar in appearance to the corresponding potassium salt.
3. Nessler's solution, added to ammonia or its salts, produces a yellow coloration, or, if the ammonia compound be present in large quantity, a brown precipitate.
4. NaHo or KHO solution when warmed with ammonia salts decomposes them, and NH3 is evolved, which is recognized by its pungent odour, by its turning red litmus paper blue, and by its forming white fumes with a strong solution of any volatile acid, e.g. HCI.
5. Heated on platinum foil, all compounds of ammonia volatilize completely.
92. SODIUM. Na, C.W. 23.
The soda salts are almost without exception soluble in water, so that the flame test alone serves to distinguish the salts of this metal.
1. Heated on platinum foil or wire in the nonluminous lamp flame, an intense yellow colour is produced, which, however, is not seen when viewed through blue glass. It is thus possible to distinguish potassium salts when mixed with sodium salts.
93 Separation of Magnesium, Potassium, Sodium,
The filtrate from the Barium Group is concentrated by evaporation, and a portion evaporated on platinum foil. If no residue is left on ignition, Mg, K, and Na are absent. Detection of Detection Detection of K and Na. N H 4:
(1.) Mg. being|(2.) Mg. being The original To a portion absent.
present. substance or so- of the concentralution is heated/ted cold solution
Evaporate an- Evaporate the with Na H0 in a add (NH4) Ho other portion of solution to drytest tube. Pre- and Na HPO4 the solution to ness, ignite resisence of Am- White crystalline dryness, ignite due, dissolve in moniumshown precipitate
de- residue, dissolve water, and add by smell, by the notes Magne- in a small quan- baryța water unwhite fumes with sium.
tity of water, fil- til the solution HCl, and by its
ter if required, has an alkaline action red
and add to the reaction; boil; filclear liquid PtCl4, ter. To filtrate, evaporate nearly add (NH4)2CO3,
to dryness, and heat, filter, evaTo detect Na.
add alcohol. Yel- porate to dryness, Evaporate alcoholic solution
precipitate and test the resi. indicates
due for K and (which must have a yellow colour,
tassium. Na. showing that excess of Pt Cl4 has
As Sub. (I.) been added) nearly to dryness, add a grain or two of sugar, and ignite residue. Exhaust with water, filter, evaporate to dryness; and if a residue be left, test it by Aame reaction for Na. Yellow coloration indicates Sodium.
REACTIONS OF THE ACIDS.
94. Grouping of the Acids.
The acids do not admit of being grouped with the same precision as the bases, but they can be approximately classified by means of certain group reagents. They are divided into two great classes, Inorganic and Organic Acids. These are readily distinguished by the action of heat.
Salts of Inorganic Acids when heated to redness are not charred; salts of Organic Acids are at once charred, owing to decomposition and consequent separation of carbon.*
95. Grouping of the Inorganic Acids.
*GROUP I. (SULPHURIC ACID GROUP). Group reagent, BaCl, in presence of HCI.
Sulphuric Acid, Hydrofluo-silicic Acid. The acids of this group are precipitated by BaCl2, and the precipitate is not dissolved on addition of HCl. * With the exception of acetic and formic acids. (See 128 and 129.)