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


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


NiSO4 is a strong electrolyte, so we have 0.0200 mol Ni2+ and 0.0200 mol SO42- in our solution. in addition, we have 0.0200 mol K+ and 0.0100 mol SO42- 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!




DAC 7/7/08 Nice problem!