25 pts . Explain the following rinciple. Write the cquation for the equilibriu o

Question

25 pts . Explain the following rinciple. Write the cquation for the equilibriu observations in terms of shiting equilibria by Le C tions in terms of shifing cquilibria by Le Chatelies CO, is insoluble in basic solution but dissolves read a. Barium chromate, BaCrO acidic solution. 5 pts ly in of NaOH to the iron(l1)- thiocyanate cquilibrium causes the red 5 pts color to disappear and a rust colored precipitate t c. The solubility of lead chloride, PbCl2, in 0.10 M HCI is 5 pts water 5 pts d. Limestone, CaCOs, is an insoluble salt but will dissolve in acid. 2. For Part C, how does the rate of the reaction vary as the temperature is increased? Explain! 5 pts

Explanation / Answer

a. BaCrO4 insoluble in basic solution but reacily dissolves in an acid. The solubility expression for BaCrO4 is

BaCrO4 (s) <=====> Ba2+ (aq) + CrO42-(aq)

Upon addition of acid, the following reaction takes place:

H+(aq) + CrO42-(aq) ----------->  HCrO4-(aq)

So as a result  CrO42- (aq) on the products side is consumed, there by decreasing the concentration of CrO42- ions

According to LeChatliers principle, since there is a decrease in concentration of CrO42- ions, the equibrium is pushed towards right side of the equation, there by increasing the solubility.

So BaCrO4 would be readily soluble in acid although insoluble in base

b. The addition of NaOH to Iron (III) thiocyanate eqilibrium causes red color to diappear and causes rust colored precipitate to form

The equilibrium reaction for Iron (III) thiocyanate is as collows:

Fe3+(aq) + SCN- (aq) <===========> [FeSCN] 2- (aq) (deep red color)

Addition of NaOH to the above equilibrium would lead to the following reaction:

Fe3+(aq) + OH- (aq) -------------> Fe(OH)2 (s)

The reddish brown ppt formed is Fe(OH)2 (s)

c. the solubility of lead chloride in 0.1M HCl is much lower than in water.

The equilibrium reaction of lead chloride, PbCl2

PbCl2 (s) <=====> Pb2+ (aq) + 2Cl-(aq)

Upon addition of 0.1 M HCl, there is an increase in the concentration of Cl- ions. According to LeChatliers principle, since there is aan increase in concentration of Cl- ions, the equibrium is pushed towards left side of the equation, there by decreasing the solubility.

So PbCl2 would be more soluble in water than HCl

d. Limestone is insoluble in water but dissolved in acid:

The solubility expression for CaCO3 is

CaCO3 (s) <=====> Ca2+ (aq) +CO32-(aq)

Upon addition of acid, the following reaction takes place:

H+(aq) + CO32-(aq) ----------->  HCO3-(aq)

So as a result CO32-(aq) on the products side is consumed, there by decreasing the concentration of CO32- ions

According to LeChatliers principle, since there is a decrease in concentration of CO32- ions, the equibrium is pushed towards right side of the equation, there by increasing the solubility.

So CaCO3 would be readily soluble in acid although insoluble in water

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