Increasing solubility Which of these salts will increase in solubility when the

Question

Increasing solubility Which of these salts will increase in solubility when the solution is acidified with a little HNO_3? AgCI, PbF_2, CuCO_3, Nis Which of these salts is more soluble in pure water than in a solution acidified with HCl? Fe_3(PO_4)_2, Pb(OH)_2, PbCl_2, BaF_2 A chemist has a mixture of solid AgBr, NaNO_3, and CuC_2O_4 salts. How could the chemist separate each salt from the others? Lead compounds have been used as paint pigments, but because the lead(II) ions is toxic, the use of lead paints in homes is now prohibited. Which of the following lead(ll) compounds would yield the greatest number of lead(II) ions when added to the same quantity of water (assuming that some undissolved solid always remains): PbCrO_4, PbSO_4+ or PbS? PbCrO_4 K_sp = 1.8 times 10^-14, PbSO_4K_sp = 1.7 times 10^-8, PbS k_sp = 2.5 times 10^-27 Note this comparison can be done conceptually only because for all three compounds K_sp = x^2.

Explanation / Answer

Q1.

if we add HNO3 --> H+ and NO3- increases

for

AgCl(s) <--> Ag+ + Cl- --> No effects

PbF2(s) <--> Pb+2 + 2F- --> F- and H+ form new equilibrium for HF(aq)

so F- decreases, and PbF2 must go into solution, there is an increase in solubility

CuCO3 --> Cu+2 + CO3-2

CO3-2 + H+ <---< HCO3-; therefore, decrease in CO3-2 will favour CuCO3 into solutions

finally

NiS(s) <--> Ni+2 + S-2;

S-2 + H+ <--> HS-

acidity will favour Ni+2 in solution, so NiS(s) increases in solution , i.e. its solubiliyy

Q2.

pure water vs. H+

Fe+3 and PO4-3 are formed, H2O will form slightly equilibrium with PO4-3; acidified will form strnog equilibrium with

H+ + PO4-3 <--> HPO4-, it increases with acidity

Pb(OH)2 <--> PB+2 + 2Oh-

2OH- + H+ --> H2O, so Pb+2 will increase, this is mroe soluble in acidic media

PbCl2 <--> Pb+2 + 2Cl- --->

Pb+2 + 2OH- <--< Pb(OH)2(s)

H+ will not help incraese, so Pb is slightly more soluble here (water)

finally

BaF2 <--> Ba+2 +2F-

Ba+2 + 2H2O <--< Ba(OH)2(s) + 2H+

OR

2F- + H+ <--> HF

this faovur strongly toward HF formation so

this is not more soluble in water

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