Analytical Chemistry potx

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Analytical Chemistry
Week 4
ENVI 15 - Analytical Chemistry
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 - Analytical Chemistry
Lecture 2
Quality Assurance
 A program to produce high quality data
with known uncertainty.
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ENVI 15 - Analytical Chemistry
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 - Analytical Chemistry

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 - Analytical Chemistry
Lecture 2
Quality Assurance
 Quality Assessment
 Performance Evaluation Samples
 Laboratory Round Robins
 Performance Audits
Analytical Chemistry
Concentration Concepts
Harris Chapter 1
3
ENVI 15 - Analytical Chemistry
Lecture 2
Atomic Mass
 Atomic mass of element = mass of one
atom of that element
 (a really, really small number!!)
ENVI 15 - Analytical Chemistry
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 - Analytical Chemistry
Lecture 2
The MOLE
 A Mole is Avogadro’s Number (6.022 x
10
23
) of atoms or molecules
ENVI 15 - Analytical Chemistry
Lecture 2
The MOLE Concept
NaCl
NaCl
NaCl NaCl
NaClNaCl
NaCl
NaCl
NaCl
NaCl
NaCl
NaClNaCl
NaCl
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ENVI 15 - Analytical Chemistry
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 - Analytical Chemistry
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 - Analytical Chemistry
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 - Analytical Chemistry
Lecture 2
Solutions
 What happens when
we put a small
amount of NaCl in
water?
 Solute and solvent
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ENVI 15 - Analytical Chemistry
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 - Analytical Chemistry
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 - Analytical Chemistry

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 - Analytical Chemistry
Lecture 2
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ENVI 15 - Analytical Chemistry
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 - Analytical Chemistry
Lecture 2
ENVI 15 - Analytical Chemistry
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 - Analytical Chemistry
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
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ENVI 15 - Analytical Chemistry
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 - Analytical Chemistry
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 - Analytical Chemistry
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 - Analytical Chemistry
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?
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ENVI 15 - Analytical Chemistry
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 - Analytical Chemistry
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 - Analytical Chemistry
Lecture 2
Buret
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ENVI 15 - Analytical Chemistry
Lecture 2
ENVI 15 - Analytical Chemistry
Lecture 2
ENVI 15 - Analytical Chemistry
Lecture 2
Reading the Buret
Estimate each reading
to ±0.01 mL
For example 13.63 mL
ENVI 15 - Analytical Chemistry
Lecture 2
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ENVI 15 - Analytical Chemistry
Lecture 2
ENVI 15 - Analytical Chemistry
Lecture 2
Pipets
TD or TC marks
ENVI 15 - Analytical Chemistry
Lecture 2
ENVI 15 - Analytical Chemistry

Lecture 2
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ENVI 15 - Analytical Chemistry
Lecture 2