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symbolic representation of a chemical
reaction that shows:
◦ reactants on left side of reaction
◦ products on right side of equation
◦ relative amounts of each with stoichiometric
coefficients
◦ attempt to show on paper what is happening at the
molecular level
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Matter is not created or destroyed, there is no
detectable change in quantity of matter in an
ordinary chemical reaction
discovered by Lavoisier
balance chemical reactions using coefficients
balancing equations is a skill acquired only
with lots of practice
propane,C3H8, burns in oxygen to give carbon
dioxide and water
C3H8 + 5 O2  3 CO2 + 4 H2O
there are equal numbers of atoms of each element on
both sides of equation
Ex. 1) How many CO molecules are required to
react with 27 formula units of Fe2O3 to make
iron and carbon dioxide
Ex. 2) What mass of CO is required to react
with 140.0 g of iron (III) oxide?
Ex. 3) How many pounds of carbon monoxide
would react with 128 pounds of iron (III)
oxide?
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Most experiments do not have the exact
amounts needed to completely react. LR helps
us decide which reactant is in excess (the one
we have plenty of) and which reactant is limiting
(the one that will determine the outcome of the
reaction)
~ If a box has 87 bolts, 113 washers and 99
nuts, how many sets consisting of one bolt, two
washers and one nut can you make?
Ex. 4) What is the maximum mass of sulfur
dioxide that can be produced by the reaction
of 95.6 g of carbon disulfide with 111 g of
oxygen? (combustion rxn) How much of the
excess chemical remains?
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Most rxns in real life do not go to completion.
A few reasons why
◦ Reactants did not react 100% to give the products
◦ Side reactions can occur to form undesirable
products as well as the wanted products
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Percent yield: The ratio of actual to
theoretical yield
actual yield
% yield =
100%
theoretica l yield
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theoretical yield is what we have been
calculating on paper - The amount of product
formed when a limiting reactant is completely
consumed. This assumes perfect conditions
and gives a maximum amount. Not likely!
actual yield is what you have made in the lab,
what really happens.
Ex. 5) A 10.0 g sample of ethanol, C2H5OH, was
boiled with excess acetic acid, CH3COOH, to
produce 15.0 g of ethyl acetate,
CH3COOC2H5. What is the percent yield? (The
other product is H2O)
Ex. 6) Using the percent yield from Ex. 5, how
much C2H5OH, is needed to give a yield of
45.0 g of CH3COOC2H5?
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Sequential ~ multiple steps are needed for a
rxn to go to completion
HNO3
Sn
C6H6  C6H5NO2  C6H5NH2
H2SO4
Conc HCl
Ex. 7) Starting with 100. g of benzene (C6H6),
calculate the theoretical yield of
nitrobenzene (C6H5NO2) and of aniline
(C6H5NH2). (1 to 1 mole ratios)
Ex. 8) If 46.7 g of aniline is prepared from
100. g of benzene, what is the percentage
yield?
define mass of 12C as 12 amu exactly
1 amu = (1/12) mass of 12C
mass of one
24Mg
atom = 24.3050 amu
experimentally determined
1 mol of 24Mg atoms = 24.3050 g
Particle
Mass (amu) Charge
-
0.00054858
-1
+
Proton (p,p )
1.0073
+1
0
1.0087
0
Electron (e )
Neutron(n,n )
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atomic weight - weighted average of the
masses of its constituent isotopes.
◦ Atoms have masses of whole numbers, HOWEVER
samples of quadrillions of atoms have a few that
are heavier or lighter isotopes due to different
numbers of neutrons present
Ex. 9) Naturally occurring chromium consists of
four isotopes. It is 4.31% 50Cr, mass =
49.946 amu, 83.76% 52Cr, mass = 51.941
amu, 9.55% 53Cr, mass = 52.941 amu, and
2.38% 54Cr, mass = 53.939 amu. Calculate
the atomic weight of chromium.
Ex. 10) Naturally occurring Lithium exists as
two isotopes, 6Li (mass = 6.015 amu) and 7Li
(mass = 7.016 amu). The atomic weight is
6.941 amu. Which isotope is more abundant?
Why?
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Mass spectrometry - is an analytical technique
that measures the mass-to-charge ratio of
charged particles.
◦ It is normally used to find the composition of a sample
by generating a mass spectrum showing the masses of
each type of component in the sample. This is how we
find the relative abundances of elements
◦ Can also be used for identification of chemical
structures, determination of mixtures, and quantitative
elemental analysis.
http://www.youtube.com/watch?v=J-wao0O0_qM
◦ Mass spectrometer or mass spectograph - a device
that measures the mass of atoms or molecules in a
given sample.
◦ Francis Aston - devised first mass spectrograph
Four factors which
determine particle’s path
in mass spectrometer
1. accelerating voltage
2. magnetic field strength
3. masses of particles
4. charge on particles
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load in a pure sample of a substance
Atoms or molecules are pushed through a beam of
high-speed electrons, which knocks electrons OFF the
atoms or molecules turning them into cations
An electric field is applied which speeds up the cations
(b/c they are repelled from the + (positive) pole and
attracted to the – (negative) pole)
The accelerated cations are sent through a magnetic
field and deflected in proportion to their mass.
Heavy cations deflect less than lighter cations and the
ions hit a detector where the measurements are
obtained from
This technique is widely used in:
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identifying unknown compounds by the mass of the
compound molecules or their fragments
determining the isotopic composition of elements in a
compound
determining the structure of a compound by observing
its fragmentation
quantifying the amount of a compound in a sample
using carefully designed methods
studying the fundamentals of gas phase ion chemistry
(the chemistry of ions and neutrals in vacuum)
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In a sample of pure neon the areas of the
“peaks” or heights of the bars indicate the
relative abundances of 20Ne, 21Ne, and 22Ne
Ex. 11) When a sample of natural copper is
vaporized and injected into a mass spectrometer,
the results shown in the figure are obtained. Use
the data to compute the average mass of natural
copper. (The mass values for 63Cu and 65Cu are
62.93 amu and 64.93 amu, respectively.)
Ex. 12) The average atomic mass of boron is
10.811 amu. The masses of the two naturally
occurring isotopes 510B and 511B, are 10.013
and 11.009 amu, respectively. Which isotope
is most common? Calculate the fraction and
percentage of each isotope.
◦ requires a little algebra
◦ remember X + (1-X) = 1
Ex. 13) Nickel has five isotopes that occur in the
following percentages and isotopic masses. What is
the isotopic mass of 60Ni?
Isotope
58Ni
60Ni
61Ni
62Ni
64Ni
Mass (amu)
57.935
?
60.931
61.928
63.928
%
68.27
26.10
1.13
3.59
0.91
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solution – a homogeneous mixture of 2 or more
substances. Usually one substance is dissolved in
another
solute – what gets dissolved
solvent – what does the dissolving (water is the
universal solvent)
concentration - amount of solute dissolved in a solvent
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Mass of solution = mass of solute + mass of solvent
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% by mass of solute = mass of solute x 100%
mass of solution
Ex. 14) Calculate the mass of potassium nitrate
required to make 277 g of solution that is 20.0%
KNO3 by mass. What is the mass of water in the
solution?
Ex. 15) What volume of 24.5% lead(II) nitrate
solutions contains 40.0g of lead(II) nitrate? The
density of the solution is 1.25 g/mL
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molarity = mol solute/L of solution = M
Ex. 16) Calculate the molarity of a solution
that contains 12.8 g of sulfuric acid in 1.70 L
of solution.
Ex. 17) Determine the mass of calcium nitrate
required to prepare 3.55 L of 0.822 M
solution.
Ex. 18) The specific gravity of concentrated
HCl is 1.185 and it is 36.31% w/w HCl. What
is its molarity? (What is the pH of the soln?)
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number of moles of
solute remains constant
M1V1 = M2V2 works
because # of moles is
constant
If 10.0 mL of 12 M HCl is
added to enough water
to give 100. mL of
solution, what is
concentration of the new
solution?
Ex. 19) What volume of 18.0 M sulfuric acid is
required to make 2.50 L of a 2.44 M sulfuric acid
solution?
M1V1 = M2V2
n1
n2
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Combine the ideas of molarity and
stoichiometry
Ex. 20) What volume of 0.500 M BaCl2 is
required to completely react with 4.32 g of
Na2SO4?
Ex. 21) a) What volume of 0.220 M NaOH will
react with 50.0 mL 0f 0.220 M aluminum
nitrate? b) What mass of aluminum hydroxide
precipitates?
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method of determining
the concentration of
solutions once the
concentration of a
standard solution is
known
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requires special
glassware
buret, pipet, flasks,
and an indicator
Ex. 22) What is the molarity of a barium
hydroxide solution if 44.4 mL of 0.103 M HCl
is required to react with 38.8 mL of the
barium hydroxide solution?
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In the lab, acid-base rxns are carried out as a
titration:
◦ Standard solution: a soln of known concentration
◦ Standardization: process by which the conc. of a
standard soln is determined.
◦ Equivalence point: point in a titration at which
chemically equivalent amounts of reactants have
reacted
◦ Endpoint: point in a titration where the indicator
changes color and the titration is stopped.
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http://apchemistrynmsi.wikispaces.com/
Each diagram (A-P) shows a sample of a
substance as viewed at the atomic level.
Characterize the contents of each container in
terms of the following categories:
I. Homogeneous mixture, heterogeneous
mixture or pure substance
II. Element(s), compound(s) or both
III. Solid, liquid, gas or combination of
phases
http://intro.chem.okstate.edu/1314F00/Lectur
e/Chapter1/Atomic.html