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A chemist designs an ion-specific probe for measuring [ Ag+] in an NaCl solution saturated with AgCl. One half-cell has an Ag-wire electrode immersed in the unknown AgCl saturated NaCl solution. It is connected through a salt bridge to the other half-cell, which has a calomel reference electrode [a platinum wire immersed in a paste of mercury and calomel ( Hg2Cl2)] in a saturated KCl solution. The measuredEcell is 0.060V. (a) Given the following standard half-reactions, calculate [Ag+ ].

Calomel:Hg2Cl2(s) + 2e-→2Hg + 2Cl-Eo= 0.24 V

Silver:Ag+(aq) +e-→Ag(s)Eo= 0.80 V

(Hint: Assume [ Cl-] is so high that it is essentially constant.) (b) A mining engineer wants an ore sample analyzed with theAg+ - selective probe. After pre-treating the ore sample, the chemist measures the cell voltage as V. What is [ Ag+]?

Short Answer

Expert verified
  1. The value is obtained as: Ag+= 4.75 M
  2. The value is obtained as: Ag+= 0.311 M

Step by step solution

01

Define chemical reaction

Chemical synthesis or, alternatively, chemical breakdown into two or more separate chemicals occurs when one component interacts with another to generate new material. These processes are known as chemical reactions, and they are generally irreversible until followed by other chemical reactions.

02

Evaluate the value of [Ag +  ]

  1. Silver is reduced at typical reduction potentials, while Hg and Cl- are oxidized.

Oxidisation: 2Hg(l)+ 2Cl-(aq)→2e-+ 2Hg2Cl2(s)Reduction: Ag+(aq)+e-→Ag(s)

Ecello= Ereducedo- EoxidisedoEcello= EAg+o- EHg2Cl2o= 0.80 V - 0.24 V= 0.56 V

It is given the we have the value as:

Ecell= 0.60 V

The Q may be extracted from the Nernst equation.

Ecell= Ecello-RTnF×±õ²Ô²Ï

The process involves two electrons, and the standard temperature is 298 K.

Ecell= Ecello-8.314Jmol K×298 Kn×96,500 C×±ô²Ô²ÏEcell= 0.56 -8.314Jmol K×298 K2×96,500 C×±ô²Ô²Ï0.60 = 0.56 -8.314Jmol K×298 K2×96,500 C×±ô²Ô²ÏlnQ =- (0.60 - 0.56) ³Õ×2×96,500 C8.314Jmol K×298 K1[Cl¯- ]2Ag+2=e- (0.60 - 0.56) ³Õ×2×96,500 C8.314Jmol K×298 K

Assume [ Cl-] is constant and [ Cl-]= 1

1[1]2Ag+2=- (0.60 - 0.56) ³Õ×2×96,500 C8.314Jmol K×298°­Ag+2=1e- (0.60 - 0.56)³Õ×2×96,500C8.314Jmol K×298°­Ag+=1e- (0.60 - 0.56)V×2×96,500C8.314Jmol K×298°­Ag+= 4.75M

Therefore, the value is: Ag+= 4.75 M

03

Evaluate the value of [Ag +  ]

a. The concentration of silver ions may be calculated using the equation in (a) and Ecell= 0.53 V.

Ag+=1e- (0.53 - 0.56) ³Õ×2×96,500 C8.314Jmol K×298°­Ag+= 0.311 M

Therefore, the value is: Ag+= 0.311 M

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