Ch 202 problem 4.87

4.87 A solution of 100.0 mL of 0.200 M KOH is mixed with a solution of 200.0 mL of 0.150 M NiSO₄.

(a) Write the balanced chemical equation for the reaction that occurs.

nice review!!! gotta make sure you still have mad skillz in writing reactions. This is just a D-D reaction from last term.

2KOH(aq) + NiSO₄(aq) -- > Ni(OH)₂(s) + K₂SO₄(aq)

note that the solubility table (table 4.1) was used to deduce that nickel (II) hydroxide is insoluble.

(b) What precipitate forms? from part (a), Ni(OH)₂.

(c) What is the limiting reactant?

YES! More mad skillz review:) Remeber how to do these? We figure out how many mol of each reactant we have (use molarity x volume), and then we identify the limiting reactant by converting mol reactant A --> mol B, and vice versa.....

starting mol KOH

starting mol NiSO₄

now convert mol KOH --> mol NiSO₄

need 0.0100 mol NiSO₄ to consume 0.020 mol KOH

convert mol NiSO₄ -> mol KOH

need 0.0600 mol KOH to consume 0.030 mol NiSO₄. We don't have enough KOH, so KOH is the limiting reactant.

now to find out how many g of precipitate form we convert mol limiting reactant to g product...

molar mass of the product (Ni(OH)₂)....

go for it....

theoretical yield of Ni(OH)₂!

(d) What is the concentration of each ion that remains in solution?

OK. For starters, we'll convert limiting reactant to the soluble product (K₂SO₄) first:

K₂SO₄ is a strong electrolyte, so our solution contains

and

from the K₂SO₄.

we started with KOH (aq), and this was the limiting reactant, so there isn't any K⁺ or OH^- from the KOH - it's all consumed.

now, remember how to figure out how much XS reactant is left after the limiting reactant is all consumed? Here, NiSO4 is in XS; we started with

starting mol NiSO₄

we consumed

need 0.010 mol NiSO₄ to consume 0.020 mol KOH

so there is

remaining.

NiSO₄ is a strong electrolyte, so we have 0.0200 mol Ni²⁺ and 0.0200 mol SO₄^2- in our solution. in addition, we have 0.0200 mol K⁺ and 0.0100 mol SO₄^2- from the soluble K₂SO₄. The final volume of our reaction mixture is 300 mL; we calculate concentrations....don't forget to add the two sources of sulfate ion!

[SO₄^2-]

[Ni²⁺]

[K+]

DAC 7/7/08 Nice problem!