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1
Analytical Chemistry
Week 4
ENVI 15 - AnalyticalChemistry
Lecture 2
Last Week We Discussed Measurement Uncertainty
-Systematic and random
error
-Accuracy vs precision
-Significant figures
-Average and standard
deviations
Quality Assurance/Quality Control
(QA/QC)
Review Harris Chapter 5
ENVI 15 - AnalyticalChemistry
Lecture 2
Quality Assurance
A program to produce high quality data
with known uncertainty.
2
ENVI 15 - AnalyticalChemistry
Lecture 2
Quality Assurance
Elements of a QA program are:
Quality Control
Quality Assessment
An accredited laboratory has a well-
developed QA/QC program
ISO 17025 – Industry Standard
ENVI 15 - AnalyticalChemistry
Lecture 2
Quality Assurance
Quality Control
Establish Method Detection and Reporting Limits
Reagent Blanks
Calibration standards
Analysis of standard reference materials
Analysis of duplicates
Recovery of known additions (spikes)
Control Charts
Analyst proficiency checks
ENVI 15 - AnalyticalChemistry
Lecture 2
Quality Assurance
Quality Assessment
Performance Evaluation Samples
Laboratory Round Robins
Performance Audits
Analytical Chemistry
Concentration Concepts
Harris Chapter 1
3
ENVI 15 - AnalyticalChemistry
Lecture 2
Atomic Mass
Atomic mass of element = mass of one
atom of that element
(a really, really small number!!)
ENVI 15 - AnalyticalChemistry
Lecture 2
Molecular Mass
Molecular mass of a molecule = mass of
one molecule
(which is the sum of the atomic masses
that make up the molecule)
(still a really, really small number!!)
ENVI 15 - AnalyticalChemistry
Lecture 2
The MOLE
A Mole is Avogadro’s Number (6.022 x
10
23
) of atoms or molecules
ENVI 15 - AnalyticalChemistry
Lecture 2
The MOLE Concept
NaCl
NaCl
NaCl NaCl
NaClNaCl
NaCl
NaCl
NaCl
NaCl
NaCl
NaClNaCl
NaCl
4
ENVI 15 - AnalyticalChemistry
Lecture 2
The MOLE
Atomic mass X 1 mole of atoms = Atomic
mass in grams
e.g. Na (22.98 amu) X 1 mole = 22.98 g
ENVI 15 - AnalyticalChemistry
Lecture 2
The MOLE
Molecular mass X 1 mole of molecules=
Molecular mass in grams
Na(22.99) + Cl (35.45) x 1 mol = 58.44 g
ENVI 15 - AnalyticalChemistry
Lecture 2
Find the Molecular Mass
BaCl
2
H
2
SO
4
Hg
2
(NO
3
)
2
Ba = 137.327 g/mol
H = 1.008 g/mol
Cl = 35.453 g/mol
S = 32.062 g/mol
O = 15.999 g/mol
Hg = 200.59 g/mol
N = 14.007 g/mol
ENVI 15 - AnalyticalChemistry
Lecture 2
Solutions
What happens when
we put a small
amount of NaCl in
water?
Solute and solvent
5
ENVI 15 - AnalyticalChemistry
Lecture 2
Concentration
Refers to how much solute is in a given
volume or mass of solvent.
Standard concentration measure in
chemistry is: # of moles / L
We call this molarity (M for short)
[Compound] = concentration of compound
ENVI 15 - AnalyticalChemistry
Lecture 2
Molarity of Sea Salts
What is the molarity of NaCl in seawater if it contains 2.7
g NaCl per 100 mL?
The molecular mass of NaCl is 22.99 (Na) + 35.45 (Cl) =
58.44 g/mol
# of moles of NaCl = 2.7 g = 0.046 mol
58.44 g /mol
ENVI 15 - AnalyticalChemistry
Lecture 2
Molarity of Sea Salts
What is the molarity of NaCl in seawater if it contains 2.7 g NaCl per
100 mL?
The molecular mass of NaCl is 22.99 (Na) + 35.45 (Cl) = 58.44 g/mol
# of moles of NaCl = 2.7 g = 0.046 mol
58.44 g /mol
100 mL = 0.100 L
[NaCl] = mol NaCl = 0.046 mol = 0.46 mol/L or M
L 0. 100 L
ENVI 15 - AnalyticalChemistry
Lecture 2
6
ENVI 15 - AnalyticalChemistry
Lecture 2
Molarity of Sea Salts
[NaCl] = mol NaCl = 0.046 mol = 0.46 mol/L
L 0. 100 L
How many millimoles of NaCl in 1 L of seawater?
How many micromoles?
ENVI 15 - AnalyticalChemistry
Lecture 2
ENVI 15 - AnalyticalChemistry
Lecture 2
Concentration
Other measures of concentration are:
g/L, mg/L, µg/L, ng/L etc
g/kg
wt%
Vol%
Parts per … ppm, ppb, ppt etc
ENVI 15 - AnalyticalChemistry
Lecture 2
Mass Concentration
What is the NaCl concentration (in mg/L) in seawater if it contains 2.7 g of
NaCl per 100 mL?
[NaCl] = 2.7 g we want answer in mg/L
NaCl (mg/L) = 2.7 g x 1000 mg x 1000 mL
100 mL
100 mL
1 g 1 L
= 2700 mg/L
7
ENVI 15 - AnalyticalChemistry
Lecture 2
Percent Concentration
Weight percent (w/w) = weight solute/weight solution x 100%
Volume percent (v/v) = volume solute/volume solution x 100%
Weight/volume (w/v) = weight solute, g/volume solution, mL x
100%
ENVI 15 - AnalyticalChemistry
Lecture 2
Percent Concentration
For %w/w and %vol/vol, the units must be
the same
A 10% (vol/vol) solution is prepared by
dissolving 10 mL of a pure substance in the
amount of solvent it takes to produce a 100
mL solution
Best done with a volumetric flask
ENVI 15 - AnalyticalChemistry
Lecture 2
Parts per Million and Parts per Billion
C
ppm
= mass solute/mass solution x 10
6
C
ppb
= mass solute/mass solution x 10
9
Note units in numerator and denominator must agree
ENVI 15 - AnalyticalChemistry
Lecture 2
Parts per Million and Parts per Billion
C
ppm
= mass solute/mass solution x 10
6
C
ppb
= mass solute/mass solution x 10
9
What is parts per trillion?
8
ENVI 15 - AnalyticalChemistry
Lecture 2
Parts per Million and Parts per Billion
C
ppm
= mass solute/mass solution x 10
6
For aqueous solutions, 1 ppm = 1 mg/L
C
ppb
= mass solute/mass solution x 10
9
For aqueous solutions, 1 ppb = ?
ENVI 15 - AnalyticalChemistry
Lecture 2
The Dilution Equation
V
1
x C
1
= V
2
X C
2
Where:
V
1
is the initial volume
C
1
is the initial concentration
V
2
is the final volume
C
2
is the final concentration
Lab Volumetric Glassware
Calibrating Burets and Pipets
ENVI 15 - AnalyticalChemistry
Lecture 2
Buret
9
ENVI 15 - AnalyticalChemistry
Lecture 2
ENVI 15 - AnalyticalChemistry
Lecture 2
ENVI 15 - AnalyticalChemistry
Lecture 2
Reading the Buret
Estimate each reading
to ±0.01 mL
For example 13.63 mL
ENVI 15 - AnalyticalChemistry
Lecture 2
10
ENVI 15 - AnalyticalChemistry
Lecture 2
ENVI 15 - AnalyticalChemistry
Lecture 2
Pipets
TD or TC marks
ENVI 15 - AnalyticalChemistry
Lecture 2
ENVI 15 - AnalyticalChemistry
Lecture 2
[...]...ENVI 15 - Analytical Chemistry Lecture 2 11 . 15 - Analytical Chemistry
Lecture 2
Buret
9
ENVI 15 - Analytical Chemistry
Lecture 2
ENVI 15 - Analytical Chemistry
Lecture 2
ENVI 15 - Analytical Chemistry. example 13.63 mL
ENVI 15 - Analytical Chemistry
Lecture 2
10
ENVI 15 - Analytical Chemistry
Lecture 2
ENVI 15 - Analytical Chemistry
Lecture 2
Pipets
TD