Part 1: 1.54×103 M AgNO3; ? M RbCl The solubility-product constant for silver ch

Question

Part 1: 1.54×103 M AgNO3; ? M RbCl The solubility-product constant for silver chloride is 2.74x1010

Determine the minimum concentration of the precipitating agent on the right to cause precipitation of the cation from the solution on the left. Answer in scientific notation with three significant figures in units of nM

Part 2: The solubility-product constants, Ksp, at 25 C for two compounds [iron(II) carbonate, FeCO3, and cadmium(II) carbonate, CdCO3] are given by the table

A solution of Na2CO3 is added dropwise to a solution that contains 1.15×102 M Fe2+ and 0.21×102 M Cd2+. What concentration of CO32 is need to initiate precipitation of the first ion? Neglect any volume changes during the addition. Answer in scientific notation with two significant figures in pM.

Explanation / Answer

A.

Formation of precipitate:

AgNO3 (aq.) + RbCl (aq.) -------------> AgCl (s) + RbNO3 (aq.)

Solubility of AgCl,

AgCl (s) = Ag+ (aq.) + Cl- (aq.)

S S S

( If S is the solubility of AgCl)

Ksp = [Ag+][Cl-]

2.74 * 10-10 = ( 1.54 * 10-3 ) [Cl-]

[Cl-] = 2.74 * 10-10 / ( 1.54 * 10-3 )

[Cl-] = 1.78 * 10-7 M

And from first equation,

[Cl-] = [RbCl]

SO, minimum concentration of RbCl needed to precipitate AgCl is 1.78 * 10-7 M

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