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ch271—analytical chemistry > Exam 3 > Flashcards

Exam 3 Flashcards

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1
Q

relative error equation

A

eR = x - μ / μ

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2
Q

chemical definition of buffer

A

weak conjugate acid-base pair

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3
Q

buffer [H3O] equation

A

[H3O]=Ka(CHA/CA)

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4
Q

buffer [OH] equation

A

[OH]=Kb(CA/CHA)

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5
Q

buffer capacity

A

how much acid/base you can add before a change in 1 pH unit

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6
Q

how to choose a buffer

A

with Ka as close to desired [H3O] or pKa as close to desired pH as possible

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7
Q

how are Ka1 and Kb2 related?

A

product is Kw

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8
Q

for H2A-, pH =

A

pH = pKa1 + pKa2 / 2

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9
Q

pH around which an indicator changes color is…

A

pKa of the indicator +/- 1

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10
Q

4 regions of acid-base titration curve, and what controls pH in each region

A

Initial (before any titrant is added) — acid analyte controls pH

Pre-equivalence point (buffer region) — remaining acid after reaction with base titrant controls pH

Equivalence point — pH is neutral (strong acid + strong base) or controlled by equilibrium (weak acid + strong base)

Post-equivalence point — pH is controlled by base titrant

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11
Q

what is special about finding pH at the pre-equivalence point in a weak acid-base titration?

A

it is a buffer, so you can use the buffer equation

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12
Q

what is special about the halfway point?

A

pH = pKa

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13
Q

[HA] = [NaX]

A

halfway point

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14
Q

what type of reaction is involved in a complexometric titration

A

Lewis acid-base

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15
Q

coordinate covalent bond

A

both e- come from one of the atoms

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16
Q

metal ions act as lewis _____, and ligand acts as lewis ______

A

metal – acid
ligand – base

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17
Q

how are ligands classified?

A

by number of donor atoms

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18
Q

ligands with one donor atom

A

monodentate

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19
Q

EDTA is a ______dentate ligand

A

hexadentate

20
Q

EDTA full name

A

ethylenediaminetetraacetate

21
Q

EDTA is an ___________ acid; ______ protic

A

aminocarboxylic
tetraprotic

22
Q

how is EDTA bought?

A

Na2H2Y · 2 H2O

23
Q

auxillary agent

A

lewis base added to keep the metal in solution at higher pH (prevents precipitation with OH)

displaced by EDTA

24
Q

masking agent

A

preferentially reacts with a non-analyte metal, allowing more specificity in complexometric titration

25
Q

indicators used for complexometric titrations

A

organic dyes
ex) calmagite; EBT

26
Q

visible light spectrum

A

380-780 nm

27
Q

definition of variables in equation for energy of a photon

A

E = energy
h = Planck constant
v = frequency
c = 2.998 x 10^8 m/s
ƛ(J) = c

28
Q

3 fundamental properties of light waves

A

speed (c)
frequency (v)
wavelength (ƛ)

29
Q

speed of light

A

2.998 x 10^8 m/s

30
Q

relationship between 3 fundamental properties of light waves

A

c = ƛv

31
Q

transmittance =

A

P / P0

32
Q

Absorbance =

A

-log (T)

33
Q

best range of absorbances to work with

A

1-2 A

(10% to 1% T)

34
Q

single standard equation

A

Aunk/Astd = Cunk / Cstd

35
Q

absorbance of a mixture is…

A

additive

36
Q

A (total) =

A

A (total) = ε1bc1 + ε2bc2

37
Q

isosbestic point

A

wavelength at which absorbance of 2 chromophores cross each other

38
Q

what is special about the isosbestic point?

A

both species have the same ε

39
Q

explain some limitations of Beer’s law

A
  • not great at high conc.
  • assume all species absorb independently
  • assume all rays pass through, no scattering
  • assume homogeneous mixture
  • assume light applied is not enough to saturate absorbing material
  • analyte may be in chemical equilibrium
40
Q

refractive index (n)

A

n = c/v

c = speed of light in a vacuum
v = speed of light in a material

41
Q

how do we take spectroscopy of an analyte in chemical equilibrium?

A

use a buffer (for an acid-base equilibrium)

measure at the isosbestic point

42
Q

chromophore

A

part of a molecule that absorbs light

43
Q

two types of light emission

A

fluorescence

phosphorescence

44
Q

explain what phosphorescence is

A

different e- spin; longer lifetime; rare

45
Q

used to measure UV spectrum

A

deuterium lamp + tungsten lamp

46
Q

selects wavelength of light in instrument

A

monochromater

47
Q

2 types of detectors

A

photomultiplier tube

photodiode array

ch271—analytical chemistry (3 decks)

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