Ba(NO3)2(aq) + NH3, does it form a PPT?

Does Ba(NO3)2 (aq) + NH3 (aq) form a PPT? According to the solubility table there shouldn't be a PPT, but during the lab I saw a slighty cloudy mixture?

Comments

  • NH3 is a weak base:

    NH3(aq) + H2O ⇄ [NH4]^+ + OH^-

    "Ammonia is moderately basic, a 1.0 M aqueous solution has a pH of 11.6" [1] so [OH]^- = 4 ×10^-3

    Ba(OH)(s) ⇄ Ba^2+(aq) + 2[OH]^-

    Ksp = [Ba^2+][OH-]^2- = 5 × 10^-3 [2] (you can find other values but it doesn't change the argument)

    [Ba^2+] = 5 × 10^-3 / [4 ×10^-3]^2 = [31.5] (!) so Ba(OH)2 will not ppt in aqueous NH3

    What I suspect is happening is that CO2 in the air is ppting BaCO3 (Ksp = 5.1 × 10^-9). It is well known that hydroxide solns absorb CO2 from the air. Did the cloudy ppt develop on standing (I'll bet you a case of beer that it did!). cheers

  • Ba No3 2 Nh3

  • Ammonia's a base, so you would suspect that barium hydroxide, Ba(OH)2, might precipitate. This compound is listed as a strong base, meaning that it ionizes in water and is soluble in water. However, I don't think it's really, really soluble, so it's possible that Ba(OH)2 precipitated anyways.

    Wikipedia lists a solubility of about 4g per 100mL water at 20C for Ba(OH)2, compared to 10.5g for Ba(NO3)2. If the Ba(NO3)2 solution was very concentrated, precipitation of Ba(OH)2 seems a likely possibility, since this salt is less soluble.

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