Worksheet: Solubility Product ULTIPLE CHOICE. Choose the one alternative that be

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Worksheet: Solubility Product ULTIPLE CHOICE. Choose the one alternative that best completes the statement or answers the question. 0.5 pts for ach question. The molar solubility of LizCO3 is74 x 10-2 M. Calculate the value of Ksp for LiCO3 1) A) 1.6 x 10-3 B) 3.6 x 10-3 C) 4.1 x 10-4 D) 5.5 × 10-3 Calculate the molar solubility of calcitum phosphate. IKsp Cag(P02-1.3 x 10-2461 2) A) 2.6 x 10-6 M B) 8.6 × 10-6 M C)1.7×10-5 M D)7.7 x 10-6 M 3) ca) At 25°C, the solubility product of Ag2S is 6 x10-51, What is the concentration of sulfide needed to form silver sulfide precipitate from 0.0010 M silver ion solution? B) 6 x 10-45 M C) 1.0 x 10-3 M D) 6 x10-48 NM A) 6 x 10-51 M

Explanation / Answer

a) Write down the dissociation of Li2CO3 as below.

Li2CO3 (s) <=====> 2 Li+ (aq) + CO32- (aq)

The solubility of Li2CO3 is equal to the solubility of CO32- (since Li2CO3 and CO32- have a 1:1 molar relationship). The solubility of Li+ will be twice the solubility of Li2CO3 (due to 1:2 nature of dissociation).

Ksp = [Li+]2[CO32-] = (2*7.4*10-2)2.(7.4*10-2)

= 1.620896*10-3 1.6*10-3

The correct answer is (A).

b) Write down the dissociation of Ca3(PO4)2. Let x be the solubility of Ca3(PO4)2.

Ca3(PO4)2 (s) <=====> 3 Ca2+ (aq) + 3 PO43- (aq)

As per the stoichiometric equation,

1 mole Ca3(PO4)2 = 3 moles Ca2+ = 2 moles PO43-.

Therefore, molar solubility of Ca2+ = 3x and PO43- = 2x.

Ksp = [Ca2+]3[PO43-]2

=====> 1.3*10-26 = (3x)3.(2x)2

=====> 1.3*10-26 = 27x3.4x2 = 108x5

=====> x5 = (1.3*10-26)/(108) = 1.20370*10-28

Take logarithm on both sides,

5*log x = log (1.20370*10-28) = -27.91948

====> log x = -5.583896

====> x = antilog (-5.583896) = 2.60677*10-6 2.6*10-6

The solubility of Ca3(PO4)2 is 2.6*10-6 M. The correct answer is (A).

c) Write down the dissociation of Ag2S as below.

Ag2S (s) <======> 2 Ag+ (aq) + S2- (aq)

Ksp = [Ag+]2[S2-]

Given [Ag+] = 0.0010 M, we have,

6*10-51 = (0.0010)2.[S2-]

=====> 6*10-51 = (1.0*10-6).[S2-]

=====> [S2-] = (6*10-51)/(1.0*10-6) = 6.0*10-45

The concentration of sulfide needed to precipitate Ag2S is 6.0*10-45 M. The correct answer is (B).

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