Explore BrainMass
Share

Electrode Chemistry

This content was STOLEN from BrainMass.com - View the original, and get the already-completed solution here!

An ammonium ion selective electrode responds to both NH4+ and H+, but not to NH3. (pKa=9.244 for NH4+)

A) What pH conditions must be imposed to ensure the electode properly represents toe activity of NH4+

B) Why is the ionic strength an important factor when using this or any ISE? How can you compensate for this effect?

C) Using the Formula EISE = constant + RT/nF ln(ai +ki,jaj), what are the TWO pH conditions that present 10% error on a measurement of 1.00 x10-4M NH4+, if kNH4+ H+ = 0.035? You may assume identical activity coefficients

© BrainMass Inc. brainmass.com October 24, 2018, 7:09 pm ad1c9bdddf
https://brainmass.com/chemistry/physical-chemistry/electrode-chemistry-59001

Attachments

Solution Preview

Please find the attached solution.

An ammonium ion selective electrode responds to both NH4+ and H+, but not to NH3. (pKa=9.244 for NH4+)

A) What pH conditions must be imposed to ensure the electrode properly represents toe activity of NH4+ (SHOW ALL MATH).

pKa = -log (Ka)

Ka = -antilog (9.244) = 5.701 x 10-10.

The pH range should be 1-8.5

B) Why is the ionic strength an important factor when using this or any ISE? How can you compensate for this effect?
Ion selective electrodes measure the concentration of ions in equilibrium at the membrane surface. In dilute solutions this is directly related to the total number of ions in the solution but at higher concentrations, inter-ionic interactions between all ions in the solution (both positive and negative) tend to reduce the mobility and thus there are relatively fewer of the measured ions in the vicinity of the membrane than in the bulk solution. Thus the measured voltage is less than it would be if it reflected the total number in the solution and this causes an erroneously low estimate of the concentration in samples with a high concentration and/or a complex matrix.
Ionic Strength is a measure of the total effect of all the ions in a solution. It is the sum of the molar concentration multiplied by the square of the valency of all the ions. The effective concentration measured at the electrode head is known as the activity of the ion. In general chemical terms it is the number of ions taking place in any chemical reaction - measured in concentration units. The activity coefficient is the ratio of the activity ...

Solution Summary

This solution answers 3 electrode chemistry questions, addressing pH conditions, ionic strength, ISE and EISE

$2.19
See Also This Related BrainMass Solution

Exam 5 Review Help

Want to verify answers for exam review.

Question 1
Consider an electrochemical cell constructed from the following half cells, linked by an external circuit and by a KCl salt bridge:

an Al(s) electrode in 1.0 M Al(NO3)3 solution
a Pb(s) electrode in 1.0 M Pb(NO3)2 solution

What is the balanced overall (net) cell reaction?

Pb(s) + Al3+(aq) Pb2+(aq) + Al(s)
3Pb(s) + 2Al3+(aq) 3Pb2+(aq) + 2Al(s)
3Pb2+(aq) + 2Al(s) 3Pb(s) + 2Al3+(aq)
Pb2+(aq) + Al(s) Pb(s) + Al3+(aq)

--------------------------------------------------------------------------------

Question 2
Calculate the value of Eocell for the following reaction:

2Au(s) + 3Ca2+(aq) 2Au3+(aq) + 3Ca(s)

-4.37 V
-1.37 V
-11.6 V
1.37 V
4.37 V

--------------------------------------------------------------------------------

Question 3
An electrochemical cell based on the following reaction has a standard cell voltage (Eocell) of 0.48 V.

Sn(s) + Cu2+(aq) Sn2+(aq) + Cu(s)

What is the standard reduction potential of tin?

Sn2+(aq) + 2e- Sn(s)

-0.14 V
0.14 V
-0.82 V
0.82 V
None of the above

--------------------------------------------------------------------------------

Question 4
Which chemical species undergoes reduction according to the following cell diagram?

Sn | Sn2+ || NO3- (acid soln), NO(g) | Pt

Sn
Sn2+
NO3-
NO
Pt

--------------------------------------------------------------------------------

Question 5
In the following half equation, which is the oxidizing agent?

NO3-(aq) + 4H+(aq) + 3e- NO(g) + 2H2O

NO3-
H+
e-
NO
H2O

--------------------------------------------------------------------------------

Question 6
Which statement is true in regard to a spontaneous redox reaction?

Eored is always negative.
Eocell is always positive.
Eoox is always positive.
Eored is always positive.

--------------------------------------------------------------------------------

Question 7
Which of the following species is the strongest oxidizing agent under standard state conditions?

Ag+(aq)
H2(g)
H+(aq)
Cl2(g)
Al3+(aq)

--------------------------------------------------------------------------------

Question 8
Calculate the cell emf for the following reaction:

2Ag+(0.010 M) + H2(1 atm) 2Ag(s) + 2H+ (pH = 10.0)

1.04 V
1.27 V
0.92 V
0.56 V
0.80 V

--------------------------------------------------------------------------------

Question 9
A current of 2.50 A was passed through an electrolytic cell containing molten CaCl2 for 4.50 hours. How many moles of calcium metal should be deposited?

5.83 x 10-5 mol
0.210 mol
0.420 mol
0.840 mol
1.95 x 109 mol

--------------------------------------------------------------------------------

Question 10
How long will it take to produce 78 g of Al metal by the reduction of Al3+ in an electrolytic cell with a current of 2.0 A?

0.01 s
420 s
13 h
116 h
1.0 x 1012 s

--------------------------------------------------------------------------------

Question 11
According to the band theory, which of the following provide(s) an explanation for the high electrical conductivity of metals?

a partly filled conduction band
a valence band overlapping an empty conduction band
a filled valence band
a large gap between the valence band and the conduction band
1 and 2
1 and 3
3
3 and 4
4

--------------------------------------------------------------------------------

Question 12
Which one of the following elements would form p-type semiconductors when added to silicon crystals?

C
P
As
Ga
Mg

--------------------------------------------------------------------------------

Question 13
The electron configuration of an Fe2+ ion is ________.

[Ar]4s24d4
[Ar]4s23d6
[Ar]3d3
[Ar]3d5
[Ar]3d6

--------------------------------------------------------------------------------

Question 14
How many 3d electrons does a Mn2+ ion have?

1
2
3
4
5

--------------------------------------------------------------------------------

Question 15
In the complex ion [Fe(CN)6]4-, the oxidation number of Fe is ________.

+1
+2
+3
-4
+6

--------------------------------------------------------------------------------

Question 16
In the complex ion [Co(en)2Br2]+, the oxidation number of Co is ________.

+1
+2
+3
-2
-1

--------------------------------------------------------------------------------

Question 17
A bidentate ligand always ________.

has bonds formed to two metal ions
has a charge of 2+ or 2-
forms complex ions with a charge of 2+ or 2-
has two donor atoms
has medical uses

--------------------------------------------------------------------------------

Question 18
Which one of the following is a monodentate ligand?

CN-
EDTA
C2O42- (oxalate ion)
H2NCH2CH2NH2 (ethylenediamine)

--------------------------------------------------------------------------------

Question 19
The best name for [Co(en)2Br2]Br is ________.

cobalt(III)bis(ethylenediamine) bromide
dibromobis(ethylenediamine)cobalt(III) bromide
dibromidedi(ethylenediamine)cobalt(III) bromide
dibromodiethylenediaaminecobalt(III) bromide
tribromobis(ethylenediamine)cobalt(III)

--------------------------------------------------------------------------------

Question 20
The correct formula for the dichlorobis(ethylenediamine)chromium(III) ion is ________.

[Cr(en)2Cl2]3+
[Cr(en)Cl2]+
[Cr(en)2Cl2]2+
[Cr(en)2Cl2]+
[Cr(en)3Cl2]+

View Full Posting Details