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CHEM 211 > Unit 3 > Flashcards

Unit 3 Flashcards

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1
Q

Activity

A

measure of the effective concentration of a species under non-ideal (e.g., concentrated) conditions. This determines the real chemical potential for a real solution rather than an ideal one.

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2
Q

Ionic strength

A

net effect of the dissolved electrolyte

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3
Q

Formula for ionic strength and define all terms

A

ionic strength (mu) = (1/2) E c*(z^2)

where E= sigma
c = concentration of ions (make sure to multiply by molar coefficients!)
z = charge (+ or - doesn’t end up mattering)

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4
Q

According to the extended dubeye-huckel equation, as ionic strength increases, the activity coefficient ___

A

decreases

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5
Q

Formula for activity and define all terms

A

a = gamma * c

gamma = activity coefficient
c = concentration
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6
Q

How does increasing ionic strength affect activity?

A

decrease

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7
Q

Effective concentration

A

??? Maybe the actual concentration of species that actually partakes in the chemical reaction

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8
Q

Fill this in:

increase ionic strength = ___ pKa = ___ Ka = ___ solubility

A

increase ionic strength = decrease pKa = increase Ka = increase solubility

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9
Q

Debye-Huckel Limiting Law and define all terms

A

log (gamma) = - 0.51 (z^2) sqrt(ionic strength)

gamma = activity coefficient
z = charge of species
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10
Q

Extended Debye-Huckel equation and define all terms

A

log (gamma) = (- A (z^2) sqrt (ionic strength))/(1 + a B sqrt(ionic strength))

gamma =activity coefficient
A and B = temperature dependent constants (should be given)
a = effective diameter of ion (dw about, should be given)

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11
Q

In a galvanic cell, where does oxidation and reduction occur (anode or cathode)

A

Anode=oxidation, cathode=reduction

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12
Q

What is the purpose of a salt bridge?

A
  • prevent direct mixing of electrolyte solutions
  • forces electrons through external circuit
  • completes circuit when ions conduct current across the salt bridge
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13
Q

What direction do electrons flow in a galvanic cell?

A

anode to cathode

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14
Q

True or false: the potential of a cell should never reach zero

A

False. Reaches zero at equilibrium

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15
Q

In the table of standard potentials, will the values be for oxidation or reduction reactions?

A

reduction

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16
Q

A positive cell potential corresponds to what type of cell?

A

Galvanic cell (spontaneous reaction)

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17
Q

A negative cell potential corresponds to what type of cell?

A

Electrolytic cell (electrical work must be done to drive the chemical reaction)

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18
Q

If you’re only given standard cell potentials for reduction reactions, how do you find the cell potential for oxidation reactions

A

Just flip the sign (magnitude of cell potential stays the same)

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19
Q

True or false: a standard potential is a measure of the driving force for a reaction from a state of unit activity for reactants and products to their equilibrium concentrations

A

True. Basically how far away a reaction is from its equilibrium

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20
Q

What does SHE stand for and what is it?

A

Standard hydrogen electrode. Basically a reference point to compare all other half-cells potentials

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21
Q

What is the SHE standard cell potential?

A

Assigned cell potential of 0.0

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22
Q

Formula for Nernst equation (at standard condition) and all terms

A

E=E(naught) - (0.0592/n) ln ([C]^c[D]^d/[A]^a[B]^b)

E(naught)= standard cell potential
n=number of moles of electrons that are transferred

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23
Q

What happens to cell potential when temperature increases?

A

Cell potential decreases (by looking at full Nernst equation):
E=E(naught) - (RT/nF) ln ([C]^c[D]^d/[A]^a[B]^b)

24
Q

What is the thermodynamic potential?

A

Difference between the cathode and anode potential when both written as reductions (look at slides POT #1 slide 40)

25
Q

What is SCE?

A

Saturated calomel electrode. Paste of Hg metal and calomel (Hg2Cl2) and KCl filling solution. Has salt bridge (ceramic frit) built inside it.

26
Q

Describe and draw the Ag/AgCl reference electrode

A

See slides POT #1 slide 44

27
Q

Potentiometry

A

use of electrode potentials to determine the concentration of analytes

28
Q

Loading error

A

When the measurement circuit draws non-trivial current and the voltage suddenly drops. Can be minimized with high resistance measurement circuits

29
Q

Draw the setup for potentiometric measurement

A

See POT #2 slide 10

30
Q

Indicators of the first kind

A

metal electrode in direct equilibrium with its metal cation in solution

31
Q

Why are indicators of the first kind not really used

A
  • Not all metal/metal cation systems establish equilibrium quickly
  • poor selectivity because it tends to react with other metals
  • some metals dissolve at low pH or are easily oxidized
32
Q

Indicators of the second kind

A
  • responds to ions that for a sparingly soluble salt with the metal (ex: silver electrode with chloride in solution
  • not really widely used (reason not really given lol)
33
Q

In a redox titration, what happens when there is a large difference in the reduction potential between titrant and analyte?

A
  • redox reaction goes further toward completion (K increases)
  • sharper end-point
34
Q

What is 1,10-phenanthrolines?

A

Redox indicator for Fe2+ and other cations. Reacts rapidly and reversibly and has a pronounce colour change

35
Q

What is starch/iodine?

A

Redox indicator. Forms a blue complex with triiodide ions (oxidizing agent) or colourless with reducing agent

36
Q

What is diphenylamine derivatives?

A

Redox indicator. Oxidized = purple, reduced = colourless

37
Q

In membrane potentials, what does an increase in charge density do to potential?

A

Increase potential

38
Q

Liquid junction potential

A

potential difference that develops across an ion permeable boundary between different electrolyte solutions because cations/anions diffuse at different rates (not a good thing, want to minimize this)

39
Q

How do you minimize the liquid junction potential?

A

Use concentrated electrolytes where the cation and anions have similar mobilities (KCl instead of NaCl, Na is much smaller than Cl)

40
Q

Boundary potential

A

difference between two membrane potentials on each side of the interface

41
Q

Formula for membrane potential

A

Eb = E1 - E2

42
Q

What affects the membrane potential of a thin glass membrane?

A

pH

43
Q

Name the three most common glass membrane materials

A

Quartz, silica glass, soda-lime silicate glass T

44
Q

The interior of a glass membrane is exposed to pH 1.0 and the exterior to pH 5.0. Which side is more negatively charged?

A

Exterior

45
Q

Draw setup for potentiometric measurements with an ISE

A

See POT #3 slide 16

46
Q

Draw a combination glass electrode

A

See POT #3 slide 17

47
Q

Formula for Ecell with pH sensitive glass electrode

A

Ecell = K - 0.0592 pH

48
Q

Draw the graph of Ecell versus pH

A

See POT #3 slide 20

49
Q

Formula for Nikolsky equation and define all terms

A

See POT #3 slide 23

50
Q

Formula for Nikolsky equation (with alkaline error) and define all terms

A

See POT #3 slide 22

51
Q

TISAB

A

Total ionic strength adjustment buffer. Increases ionic strength to a very high level so that the ionic strength of the sample and calibration standards are roughly the same (even though the sample ionic strength is unknown).

52
Q

Possible errors with glass electrodes (2 main categories)

A

Chemical and user errors

53
Q

Give three examples of chemical errors

A
  • junction potential different between standard and sample
  • junction potential drifts over time
  • alkaline error
  • acid error (electrode response decreases at pH less than 1)
54
Q

Give three examples of user errors

A
  • standards used for calibration curves aren’t accurate
  • glass membrane not clean
  • glass not fully hydrated
  • insufficient time to reach equilibrium (but really shouldn’t take that long)
55
Q

3 types of ion selective electrodes

A
  • glass
  • solid-state (crystalline)
  • liquid membranes

CHEM 211 (5 decks)

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