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In each case below, a solution is known to contain one of the two compounds listed. Suggest a single reagent, based on tests used in this experiment, to identify the compound. State the reagent to be added, the observation, and the conclusion. a) KOH and KCI b) NH_4Cl and KCl c) Fe(NO_3)_3 and Al(NO_3)_3 d) K_2CrO_4 and KNO_3 A solution is known to contain one of the following ions: Hg_2^2+, Sr^2+, Cs^+. Refer to a solubility rules table from your text to suggest how the identity might be determined.
Expert Answer
Question 4.
a)
KOH = strong base, will have a high pH, if we add HCl, expect neutralization, heat must be released, i.e. T will increase
KCl = this is ionic salt K+ and Cl- will be in solution, Add Hg2+ ions in order to precipitate HgCl2. If solid forms, then this is ionic.
Also, flame test shoudl show K+ ion color in flames as purple
b)
NH4Cl = this is slightly acidic, should react with any base to form NH3(g) + OH- + H+ = H2O
KCl = use flame test, if violet flame is seen, this contains K+ ions
c)
Fe(NO3)3
Fe3+ ions can be detected by:
Fe(NO3)3 + 6 KSCN = K3[Fe(SCN)6] + 3 KNO3
the solution complex will form a dark -red color
For Al(NO3)
Al3+ is present, it must be in basic media so:
The aluminum ion gets involved the adsorption of the red dye aluminon (which is actually the species – aurin tricarboxylic acid).
The Al(OH)3 will be seen as a precipitate with this dye.
d)
K2CrO4 = 2K+ + CrO4-2
Add Ag+ ions, they will preicpitate with
2Ag+ + CrO4-2 = Ag2CrO4(s)
if no precipitate forms, this should be the KNO3 solution.
Use flame test to identify its color (violet) and presence
