Exam 3

Question 1

relative error equation

Answer 1

eR = x - μ / μ

Question 2

chemical definition of buffer

Answer 2

weak conjugate acid-base pair

Question 3

buffer [H3O] equation

Answer 3

[H3O]=Ka(CHA/CA)

Question 4

buffer [OH] equation

Answer 4

[OH]=Kb(CA/CHA)

Question 5

buffer capacity

Answer 5

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

Question 6

how to choose a buffer

Answer 6

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

Question 7

how are Ka1 and Kb2 related?

Answer 7

product is Kw

Question 8

for H2A-, pH =

Answer 8

pH = pKa1 + pKa2 / 2

Question 9

pH around which an indicator changes color is…

Answer 9

pKa of the indicator +/- 1

Question 10

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

Answer 10

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

Question 11

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

Answer 11

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

Question 12

what is special about the halfway point?

Answer 12

pH = pKa

Question 13

[HA] = [NaX]

Answer 13

halfway point

Question 14

what type of reaction is involved in a complexometric titration

Answer 14

Lewis acid-base

Question 15

coordinate covalent bond

Answer 15

both e- come from one of the atoms

Question 16

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

Answer 16

metal – acid
ligand – base

Question 17

how are ligands classified?

Answer 17

by number of donor atoms

Question 18

ligands with one donor atom

Answer 18

monodentate

Question 19

EDTA is a ______dentate ligand

Answer 19

hexadentate

Question 20

EDTA full name

Answer 20

ethylenediaminetetraacetate

Question 21

EDTA is an ___________ acid; ______ protic

Answer 21

aminocarboxylic
tetraprotic

Question 22

how is EDTA bought?

Answer 22

Na2H2Y · 2 H2O

Question 23

auxillary agent

Answer 23

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

displaced by EDTA

Question 24

masking agent

Answer 24

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

Question 25

indicators used for complexometric titrations

Answer 25

organic dyes ex) calmagite; EBT

Question 26

visible light spectrum

Answer 26

380-780 nm

Question 27

definition of variables in equation for energy of a photon

Answer 27

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

Question 28

3 fundamental properties of light waves

Answer 28

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

Question 29

speed of light

Answer 29

2.998 x 10^8 m/s

Question 30

relationship between 3 fundamental properties of light waves

Answer 30

c = ƛv

Question 31

transmittance =

Answer 31

P / P0

Question 32

Absorbance =

Answer 32

-log (T)

Question 33

best range of absorbances to work with

Answer 33

1-2 A (10% to 1% T)

Question 34

single standard equation

Answer 34

Aunk/Astd = Cunk / Cstd

Question 35

absorbance of a mixture is...

Answer 35

additive

Question 36

A (total) =

Answer 36

A (total) = ε1bc1 + ε2bc2

Question 37

isosbestic point

Answer 37

wavelength at which absorbance of 2 chromophores cross each other

Question 38

what is special about the isosbestic point?

Answer 38

both species have the same ε

Question 39

explain some limitations of Beer's law

Answer 39

- 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

Question 40

refractive index (n)

Answer 40

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

Question 41

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

Answer 41

use a buffer (for an acid-base equilibrium) measure at the isosbestic point

Question 42

chromophore

Answer 42

part of a molecule that absorbs light

Question 43

two types of light emission

Answer 43

fluorescence phosphorescence

Question 44

explain what phosphorescence is

Answer 44

different e- spin; longer lifetime; rare

Question 45

used to measure UV spectrum

Answer 45

deuterium lamp + tungsten lamp

Question 46

selects wavelength of light in instrument

Answer 46

monochromater

Question 47

2 types of detectors

Answer 47

photomultiplier tube photodiode array