1. a) What species are present in a 3.0 M NH3 solution? b) Qualitatively, what is the pH of this solution? c) What reaction(s) might occur when this solution is added to a solution containing Mn2+? d) What effect will adding HNO3 to the solution from part c have? Write any chemical equations that explain your answer.
a). NH3, NH4^+, OH^-, H3O^+
b) NH3 is a weak base so you know it will be basic and you might guess pH 10 or so.
c) Mn^2+ + 2OH^- ==> Mn(OH)2(s)
d) Adding HNO3 would react with the OH^- of Mn(OH)2 to product H2O and the ppt would dissolve because the OH^- has been decreased.
is there any way to calculate B?
Yes if you have Kb.
The problem says "qualitatively" which means make the best educated guess. Qualitative in that sense always means to make the best estimate.
If you know Kb (which is 1.8E-5) you can calculate it as follows:
..........NH3 + HOH ==> NH4^+ + OH^-
I.........3..............0........0
C........-x..............x........x....
E.........3-x............x........x
Kb = (NH4^+)(OH^-)/(NH3)
1.8E-5 = (x)(x)/(3-x). To get rid of a quadratic equation we usually assume 3-x = 3 (and in this case it is essentially true and making the assumption it will not change the answer) then
5.4E-5 = x^2
x = 0.0073 = (OH^-)
So pOH = -log(0.0073) = 2.13 and
pH + pOH = pKw = 14 so
pH = 14-2.13 = about 11.9
a) In a 3.0 M NH3 solution, the species present are NH3 (ammonia) molecules.
b) Qualitatively speaking, the pH of this solution will be basic. You can think of it as being "ammonia-nal"! (Ammonia + Alkaline = Ammonia-nal, get it?)
c) When the NH3 solution is added to a solution containing Mn2+, a potential reaction that might occur is the formation of a complex between ammonia and manganese ions. This complex can be expressed by the equation:
2 NH3 + Mn2+ → [Mn(NH3)2]2+
d) When HNO3 (nitric acid) is added to the solution from part c, it will neutralize some of the basicity provided by the ammonia. The resulting reaction can be represented as:
HNO3 + NH3 → NH4+ + NO3-
So, adding HNO3 will decrease the basicity and increase the acidity of the solution.
a) To determine the species present in a 3.0 M NH3 solution, we need to consider the dissociation of ammonia (NH3) in water. When ammonia dissolves in water, it acts as a weak base and undergoes a partial ionization. The equation for this dissociation is:
NH3 + H2O ⇌ NH4+ + OH-
In this equation, NH4+ is the ammonium ion and OH- is the hydroxide ion. Therefore, in a 3.0 M NH3 solution, we would have NH4+ and OH- ions present along with undissociated NH3 molecules.
b) To qualitatively determine the pH of the solution, we need to consider the concentration of OH- ions. NH3 is a weak base, so it will produce OH- ions through its partial dissociation. In a solution containing NH3, the concentration of OH- ions will be higher than the concentration of H+ ions (from water dissociation).
Since OH- ions are responsible for the basicity of a solution, we can conclude that the NH3 solution will have a pH greater than 7. It will be alkaline/basic.
c) When the NH3 solution is added to a solution containing Mn2+, several reactions can occur depending on the conditions. One possible reaction is the formation of a complex between NH3 and Mn2+. This reaction can be represented by the following equation:
[Mn(H2O)6]2+ + 6NH3 ⇌ [Mn(NH3)6]2+ + 6H2O
In this reaction, [Mn(H2O)6]2+ represents the hydrated Mn2+ ion, and [Mn(NH3)6]2+ represents the complex formed between Mn2+ and NH3.
d) When HNO3 is added to the solution containing the complex [Mn(NH3)6]2+, it will react with NH3 to form ammonium nitrate. The reaction equation is as follows:
HNO3 + NH3 ⇌ NH4NO3
In this equation, NH4NO3 represents ammonium nitrate, which is formed by the combination of HNO3 (nitric acid) and NH3 (ammonia).
Overall, the addition of HNO3 to the NH3 solution will result in the formation of ammonium nitrate, and the pH of the solution may change depending on the concentration of HNO3 added.