lOMoARcPSD|50207110
Analytical Chemistry Chapter One Introduction and Fundamentals
Chapter 1
1.Introduction to Analytical Chemistry
Chemistry is the study of matter, including its composition and structure, its
physical properties, and its reactivity. There are many ways to study chemistry, but,
we traditionally divide it into five fields: organic chemistry, inorganic chemistry,
biochemistry, physical chemistry, and analytical chemistry.
Analytical chemistry is often described as the area of chemistry responsible
for 1. Characterizing the composition of matter, both qualitatively and quantitatively,
2. 3.
Improving established analytical methods, Extending existing analytical
4.
methods to new types of samples, and Developing new analytical methods for
measuring chemical phenomena.
2. Measurements in Analytical Chemistry
Units of Measurement
A measurement usually consists of a unit and a number expressing the quantity
of that unit. We may express the same physical measurement with different units,
which can create confusion.
To ensure consistency, and to avoid problems, scientists use a common set of
fundamental units. These units are called SI units after the Système International
d’Unités. Sometimes it is preferable to express measurements without the
exponential term, replacing it with a prefix (Table 1.1). A mass of 1×10–15 g, for
example, is the same as 1 fg, or femtogram.
1
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Analytical Chemistry Chapter One Introduction and Fundamentals
Table 1.1 Common Prefix for Exponential Notation
Question: What Is a Mole and Why Are Moles Used?
Answer: A mole is simply a unit of measurement. Units are invented when existing
units are inadequate. Chemical reactions often take place at levels where using
grams wouldn't make sense, yet using absolute numbers of atoms/molecules/ions
would be confusing, too.
Like all units, a mole has to be based on something reproducible قابل لإلعادة. A mole
is the quantity of anything that has the same number of particles found in 12.000
grams of carbon-12.
That number of particles is Avogadro's Number, which is roughly 6.02 x 1023. A
mole of carbon atoms is 6.02x1023 carbon atoms. A mole of chemistry teachers is
6.02x1023 chemistry teachers. It's a lot easier to write the word 'mole' than to write
'6.02x1023' anytime you want to refer to a large number of things! Basically, that's
why this particular unit was invented.
Why don't we simply stick with units like grams (and nanograms and kilograms,
etc.)? The answer is that moles give us a consistent method to convert between
atoms/molecules and grams. It's simply a convenient unit to use when performing
calculations.
The number of grams in a mole is different from substance to substance. If you're
like most students, it's this that's confusing you. Picture it this way: a dozen
elephants have a different weight than a dozen rabbits- but in each case, you have a
2
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Analytical Chemistry Chapter One Introduction and Fundamentals
dozen animals. Similarly, a mole of oxygen gas has a different weight than a mole of
water- but in each case, you have 6.02×1023 molecules.
Weight g /molecular wt. g/mol.= moles
2.1 Uncertainty in Measurements
A measurement provides information about its magnitude and its uncertainty.
Consider, for example, the balance in Figure 1.1, which is recording the mass of a
cylinder. When weighing an object on a balance, the measurement fluctuates in the
final decimal place. We record this cylinder’s mass as 1.2637 g ± 0.0001 g. mass as
1.2637 g ± 0.0001 g, indicating both its magnitude and its absolute uncertainty.
Suppose you weigh a sample on a balance that measures mass to the nearest ±0.1
mg. reporting the sample’s mass as 1.762 g instead of 1.7623 g is incorrect because
it does not properly convey the measurement’s uncertainty. Reporting the sample’s
mass as 1.76231 g also is incorrect because it falsely suggest an uncertainty of ±0.01
mg or ±0.00001g.
2.2 Accuracy
The closeness of an experimental measurement or result to the true or accepted
value.
2.3 Precision
The random or indeterminate error associated with a measurement or result.
Sometimes called the variability, it can be represented statistically by the standard
deviation or relative standard deviation (coefficient of variation)
2.4 Concentration
Concentration is a general measurement unit stating the amount of solute present
in a known amount of solution: or (The ratio of the amount of solute to the amount
of solution.) Although we associate the terms “solute” and “solution” with liquid
samples, we can extend their use to gas-phase and solid-phase samples as well.
3
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Analytical Chemistry Chapter One Introduction and Fundamentals
The following table shows examples of solution in liquid, gaseous, and solid
states of matter.
Table 1.2 Solution of Different States of Matter.
State of Matter Solvent Solute Solution
Liquid Water Acetic Acid Vinegar
Gas Nitrogen Oxygen Air
Solid Copper Tin Bronze
2.5 Solution
A homogenous mixture of molecules or ions.
2.6 Solvent
The medium in which the molecules or ions are dissolved.
2.7 Solute
Any substance dissolved in a solvent.
2.8 Analyte
Constituent of the sample which is to be studied by quantitative measurements or
identified qualitatively.
2.9 Molarity
Molarity express concentration as moles of solute per liter of solution (number
of moles of solute in one litre of solution). Molarity is the concentration of a
particular chemical species.
Molarity is used so frequently that we use a symbolic notation to simplify its
expression in equations and in writing. Square brackets around a species indicate
that we are referring to molarity. Thus, [Na+] is read as “the molarity of sodium
ions.
2.10 Normality
Normality is a concentration unit that is no longer in common use. Normality
defines concentration in terms of an equivalent, in one litre of solution, which is the
4
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Analytical Chemistry Chapter One Introduction and Fundamentals
Chapter 1
1.Introduction to Analytical Chemistry
Chemistry is the study of matter, including its composition and structure, its
physical properties, and its reactivity. There are many ways to study chemistry, but,
we traditionally divide it into five fields: organic chemistry, inorganic chemistry,
biochemistry, physical chemistry, and analytical chemistry.
Analytical chemistry is often described as the area of chemistry responsible
for 1. Characterizing the composition of matter, both qualitatively and quantitatively,
2. 3.
Improving established analytical methods, Extending existing analytical
4.
methods to new types of samples, and Developing new analytical methods for
measuring chemical phenomena.
2. Measurements in Analytical Chemistry
Units of Measurement
A measurement usually consists of a unit and a number expressing the quantity
of that unit. We may express the same physical measurement with different units,
which can create confusion.
To ensure consistency, and to avoid problems, scientists use a common set of
fundamental units. These units are called SI units after the Système International
d’Unités. Sometimes it is preferable to express measurements without the
exponential term, replacing it with a prefix (Table 1.1). A mass of 1×10–15 g, for
example, is the same as 1 fg, or femtogram.
1
Downloaded by Samuel Gero ()
, lOMoARcPSD|50207110
Analytical Chemistry Chapter One Introduction and Fundamentals
Table 1.1 Common Prefix for Exponential Notation
Question: What Is a Mole and Why Are Moles Used?
Answer: A mole is simply a unit of measurement. Units are invented when existing
units are inadequate. Chemical reactions often take place at levels where using
grams wouldn't make sense, yet using absolute numbers of atoms/molecules/ions
would be confusing, too.
Like all units, a mole has to be based on something reproducible قابل لإلعادة. A mole
is the quantity of anything that has the same number of particles found in 12.000
grams of carbon-12.
That number of particles is Avogadro's Number, which is roughly 6.02 x 1023. A
mole of carbon atoms is 6.02x1023 carbon atoms. A mole of chemistry teachers is
6.02x1023 chemistry teachers. It's a lot easier to write the word 'mole' than to write
'6.02x1023' anytime you want to refer to a large number of things! Basically, that's
why this particular unit was invented.
Why don't we simply stick with units like grams (and nanograms and kilograms,
etc.)? The answer is that moles give us a consistent method to convert between
atoms/molecules and grams. It's simply a convenient unit to use when performing
calculations.
The number of grams in a mole is different from substance to substance. If you're
like most students, it's this that's confusing you. Picture it this way: a dozen
elephants have a different weight than a dozen rabbits- but in each case, you have a
2
Downloaded by Samuel Gero ()
, lOMoARcPSD|50207110
Analytical Chemistry Chapter One Introduction and Fundamentals
dozen animals. Similarly, a mole of oxygen gas has a different weight than a mole of
water- but in each case, you have 6.02×1023 molecules.
Weight g /molecular wt. g/mol.= moles
2.1 Uncertainty in Measurements
A measurement provides information about its magnitude and its uncertainty.
Consider, for example, the balance in Figure 1.1, which is recording the mass of a
cylinder. When weighing an object on a balance, the measurement fluctuates in the
final decimal place. We record this cylinder’s mass as 1.2637 g ± 0.0001 g. mass as
1.2637 g ± 0.0001 g, indicating both its magnitude and its absolute uncertainty.
Suppose you weigh a sample on a balance that measures mass to the nearest ±0.1
mg. reporting the sample’s mass as 1.762 g instead of 1.7623 g is incorrect because
it does not properly convey the measurement’s uncertainty. Reporting the sample’s
mass as 1.76231 g also is incorrect because it falsely suggest an uncertainty of ±0.01
mg or ±0.00001g.
2.2 Accuracy
The closeness of an experimental measurement or result to the true or accepted
value.
2.3 Precision
The random or indeterminate error associated with a measurement or result.
Sometimes called the variability, it can be represented statistically by the standard
deviation or relative standard deviation (coefficient of variation)
2.4 Concentration
Concentration is a general measurement unit stating the amount of solute present
in a known amount of solution: or (The ratio of the amount of solute to the amount
of solution.) Although we associate the terms “solute” and “solution” with liquid
samples, we can extend their use to gas-phase and solid-phase samples as well.
3
Downloaded by Samuel Gero ()
, lOMoARcPSD|50207110
Analytical Chemistry Chapter One Introduction and Fundamentals
The following table shows examples of solution in liquid, gaseous, and solid
states of matter.
Table 1.2 Solution of Different States of Matter.
State of Matter Solvent Solute Solution
Liquid Water Acetic Acid Vinegar
Gas Nitrogen Oxygen Air
Solid Copper Tin Bronze
2.5 Solution
A homogenous mixture of molecules or ions.
2.6 Solvent
The medium in which the molecules or ions are dissolved.
2.7 Solute
Any substance dissolved in a solvent.
2.8 Analyte
Constituent of the sample which is to be studied by quantitative measurements or
identified qualitatively.
2.9 Molarity
Molarity express concentration as moles of solute per liter of solution (number
of moles of solute in one litre of solution). Molarity is the concentration of a
particular chemical species.
Molarity is used so frequently that we use a symbolic notation to simplify its
expression in equations and in writing. Square brackets around a species indicate
that we are referring to molarity. Thus, [Na+] is read as “the molarity of sodium
ions.
2.10 Normality
Normality is a concentration unit that is no longer in common use. Normality
defines concentration in terms of an equivalent, in one litre of solution, which is the
4
Downloaded by Samuel Gero ()
