Study Material for Final Exam in CHM-102 (all sections)
Outlined by: Ryan Rettinger, Graduate Student
University of Rhode Island, Department of Chemistry
The following material is designed to emphasize concepts, equations and observations
you may be responsible for understanding during the final exam. I am neither
responsible for making the final, nor is any of this material guaranteed to be on it;
rather, this material is a breakdown of important concepts whose study will better equip
you with the skills needed to do well.
Notation: Each lab will be broken down as follows:
Lab X (Lab titile)
Key Concepts:
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This section will include the ideas and units involved, and will state
the purpose of the lab, along with general information and tips about
understanding them.
Equations:
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As titled, this section will list equations used in calculation section of the
lab. You will be responsible for knowing what EVERY variable means, and
when to use it.
Note: Be careful of subscripts (understand what’s involved)
Sample problem(s):
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This section will be similar to the “Quiz information“ section in the lab
manual. It may include specific example problems or, “if I gave you this and
this, you should be able to find this” format, or both.
Red Flags:
·
This section will include things to help you understand when you are dealing
with calculations from this section. It may also include hints of how to
recognize certain approaches to a solution. This may or may not be what you
learned in lecture, you’re responsible for getting the answer, not a certain
thought path.
Each of our 10 labs will be broken down in this fashion. This outline will help
with understanding the right answer, instead of just seeing an “X” on a wrong
answer. Lab 1 (Density)
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Key concepts
Use balance to find mass
Measuring volume by two methods
● Measuring with a ruler, calculating volume from Diameter and height.
● Measuring water displacement in Graduated cylander
Calculating density by measuring both mass and volume
Equations:
Eq. 1) D=M/V
Density equals mass divided by volume
Eq.2) Vcylinder= π r2 h
The volume of a cylander is pi times the radius squared times the
hight of the cylander
Eq. 3)
%error=I exp.-accept I/ accept
Sample problems:
A cylinder has mass (58g) and volume (27mL). What is the density
The density of Cu is (8.96g/mL). What mass would a cylinder with Diameter (2.5cm) and height
(25cm) weigh?
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Red Flags:
This concept appears again throughout the semester. When you need to find the mass of
something (often a solution or a solid) and you can find the mass of a certain volume, you can find
the density. Also, if you know the density (usually given in the problem) and you know the volume
(ie an acid solution receiving heat from a chemical reaction) you can find the mass of solution using
eq.1.
Lab 2 (Paper Chromatography)
Key concepts
● Using Paper Chromatography as a separation technique for the separation of marker ink on a
TLC plate
● Understanding that different inks wick up the plate differently in different solvents
● Mobile phase: travelling solvent (used H2O, Isopropanol, and salt water)
● Stationary phase: TLC plate (like a coffee filter)
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Equations
Eq. 4)
Rf=Distspot/Distsolvent
The retention factor is equal to the distance the spot
traveled divided by the distance the solvent traveled
%error (refer Eq. 3)
Sample problem:
● If I give you a chromatogram, you should be able to measure the variables with a ruler, and
calculate Rf.
Red Flags:
Easy to spot, if the words chromatogram, chromatography, Rf, etc, are used, this is what they’re
talking about. Please realize that the retention factor is length/length units, and therefore is unitless
as an intensive, experiment-specific constant.
Lab 3 (Tracking zinc through chemical reactions)
Key concepts
● Molar Mass
● Stoichiometry
● Be able to balance equations (non-redox for this lab)
● Understand the mol:mol ratio between two components by looking at the balanced chemical eq.
● Limiting reagent
● Make observations about the reactions step to step:
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-Acid bubbled profusely when added to ZnCO3, but only subtly dissolved
ZnO.
-ZnOH was a gelatinous insoluable white solid
Use stoichiometry to do calculations, if total reaction of limiting reagent is assumed
Using centrifuge and filtration to separate aqueous and precipitate
Equations:
Eq.5)
gx/Mx=molx
The grams of x divided by the Molar mass of x
(obtained from the periodic table) equals the #of moles of substance x.
Eq.6)
molx(Amoly/Bmolx)=moly
If the moles of substance x are known, the
moles of substance y can be found via multiplication of the correct orientational ratio of the
stoichiometric coefficients (A and B). The stoichiometric coefficients are the numbers placed in
front of the reactants or products in the balanced chemical equation. The correct orientation is
that which places the moles of substance you already know in the denominator, and those you
want in the numerator. This is analogous to any simple unit conversion, only the stoichiometric
coefficients convert moles of one substance to another for a specific chemical reaction.
Sample Questions:
If I give you the balanced chemical reaction, and the number of grams of each reactant, you
should be able to find:
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The number of moles of each reactant
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The limiting reagent
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The number of moles of each product formed, if the limiting reagent is completely
consumed.
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The excess amount of the non limiting reactants
Consider the Chemical equation:
Pb(NO3)2+ NaCl -------> NaNO3 + PbCl2(s)
● Balance the reaction
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Coefficients should be 1:2:2:1
● Find the limiting reagent if I have 5g of each reactant
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Use eq. 5 to find the number of moles of each reactant that can contribute to the
reaction, and divide that by its stoichiometric coefficient. Whichever reactant has
the lower number contributes least to the reaction, and thus is the limiting reagent.
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Note: For any further calculations, use only the number of moles of limiting
reactant, because once it is used up, there can be no more reaction.
Find
the
amount
(in grams) of PbCl2 made from these amounts.
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Use Eq. 6 to convert mol (limiting reactant) to mol (PbCl2)
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Use a manipulation of Eq.5 to calculate grams of PbCl2
Red Flags:
You should expect to be using stoichiometry when you see a balanced chemical reaction, or
when the reactants are given, and you must predict the products. Always understand that as long
as you know the balanced chemical eq, and how many mols of a substance are reacting, you can
convert that to moles of another substance with eq.6.
Be prepared to use stoichiometric ratios comfortably. Be comfortable balancing chemical
equations, and using the balanced coefficients to make calculations.
Recognize you cannot convert from Grams of reactant to grams of product. Only through a
stoichiometric conversion can you find something like that. A visual representation is given in «Key
Concepts in CHM-102».
Lab 4 (Acid base Titrations):
Key Concepts
Understand
dilutions
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● Understand titrations (burette, indicator)
● Phenolpthalene: be able to spell it perfectly!
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I’m kidding. Just know its pink in a base (Blushes in a Base), clear in acid
Equations
Eq. 7a) Mx=molx/Vx (definition of Molarity- or concentration) The molarity is defined by the
ratio of moles of solute to liters of solution. Rearranged usefully:
Eq. 7b) MxVx=Molx
Eq.8a) the dilution mole balance: mol1=mol2 .
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In other words, the moles of solute before and after you add the dilluting solvent are the same.
(Duh, if you didn't add any solute, only solvent, the moles of solute is the same.) Now, if you rewrite
Eq. 8a knowing from Eq. 7b that mol1=concentration1*Volume1, and likewise for state 2, Eq 7a is
written:
● Eq. 8b) the dilution mole balance: M1V1=M2V2 (This is what's given in the lab manual)
● Eq.9) The titration mole balance (note: not taught in lecture)
(1/A) MolAcid=(1/B) Mol Base
(A and B are the stoichiometric coefficients in front of the acid and base, respectively.
The terms in Eq.8a can be reinterpreted by Eq. 7b (Molx=Concentrationx * Volumex)
leaving: Eq. 8b) (1/A) MacidVacid=(1/B) MbaseVbase
● Using the same A and B as before, the question will give you all but 1 of these 4 variables, and
you will just have to algebreically manipulate them to solve for yours.
Sample Questions
● Dilutions:
○ I should be able to give you the stock acid concentration, and ask you how much of it I
should use to make some volume of another concentration.
○ Make 25mL of 5M HCl from stock 12M. How much 12M HCl is needed?
Soln: .025=V2; 5=M2; 12=M1; find V1. (Use Eq. 7&8)
● Titrations:
● Given chemical composition of the acid and base, you should be able to:
○ Predict the products. Generic Rxn: HA + BOH
BA + H2O
○ Balance the Chemical equation
● Given both the concentration and volume used of either the acid or base, you should be able to
predict in order:
○ The number of moles for the substance which both M and V were given (Eq. 7b)
○ The number of moles of the other reactant (Eq. 6)
○ Now that the number of moles are known, whichever (M or V) is not given will be
asked for, and using Eq. 7a, you can find it.
Red Flags:
Understanding and application of these equations is not only applicable in titrations. This
material covers many concepts:
● Stoichiometry
● Balancing Chemical equations
● Unit conversion (mL to L, g to Mol, etc…)
Use Eq. 7 and 8 for any chemical reaction (ie. Redox titrations-next lab)
Lab 5 (RedOx Titrations)
Key Concepts
● Understand how to balance and use redox chemical equations
● Incorporate past concepts to a redox titration
● Terms like Oxidizing agent/ Reducing agent…. Know the difference, and how to determine
which is which
● Mass% and Mole%
● Steps to balance REDOX:
1.
Determine what elements are changing charges from the reactant’s side of the reaction to the
product’s side. Sometimes the oxidation state of an element must be found by knowing what
it’s given as bonded to (ie. (MnO4-) : the oxidation state of Mn is +7 because oxygen is always
(-2); in Pb2(SO4)3, the oxidation state of Pb is +3 because SO4 is always (-2). If an element
appears by itself (Fe(S), Hg(l), O2(g)), its oxidation state is 0.
2. Write for those two elements (found in step 1) a half reaction
3. Balance elements (using H2O and H+ appropriately)
4. Balance Charges/Electrons
Understand that Fe+2 and Fe+3 are not the same. One of them is missing an electron. Fe+2 has
one more electron than Fe+3 because it’s charge is lower. Add an electron to the side in which the
½-reaction is deficient.
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Make considerations to study the mass% calculations in the discussion questions for this one.
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Equations:
Eq. 10) Mass percent of element 'x' in a molecule:
mass%X=Mx/Mtotal molecule
(Mx is the Molar Mass of element x)Understand that Mtotal molecule may be the total molecule, the total
mixture, the total anything. The question must state what % is x in what.
Sample Problems
(solve the one in the manual we solved before the experiment)
Red Flags:
You will know if you have a redox reaction if you can find something that changes oxidation
state from one side of the reaction to the other. If you go through and assign oxidation states to
everything, and everything’s oxidation state stays the same, you don’t have a redox.
Lab 6 (Ideal Gas Law)
Key Concepts:
● Use the ideal gas law to determine the Ideal gas constant “R”
● Experimentally determine (using temperature probes, graduated cylinders, barometers, and the
method of bubbling gas through water to obtain all the other variables in the Ideal Gas eq.
● Know a couple of conditions for ideality (remember the prelab)
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Equations
Eq.11) The ideal gas equation of state:
PV=nRT
Sample Questions:
● Given any 4 of the 5 variables in Eq. 11, be able to calculate the 5th.
● Know that only when you’re bubbling gas through a liquid you have to consider the Vapor
pressure of the liquid. We knew that because the liquid in and out of the cylander was even,
that the pressure inside must be the same as the outside, or Patm=Pcyl. However, the P inside
the cylander was both the pressure of the gas of interest plus the water pressure. Therefore:
Patm =Pgas+Pwater. Be sure to use the right pressure in Eq. 11.
Red Flags:
You all did well on this lab, so I’m not worried about this one. Just remember that you may have
to do some stoichiometry to get the 'n' term. In this lab we used the amount of magnesium to
calculate the number of moles of gas produced.
Lab 7 (Calorimetry)
Key Concepts:
● Heat capacity and specific heat (introducing Joules as the unit of energy)
● Enthalpies of Reactions (dissolving a salt, and acid-metal rxns)
● Understand Exothermic and endothermic
● Introduce q (heat)
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Equations
Eq.12) Energy balance
-qlost=qgained
Note: only when ∆E=0; w=0 (i.e. in a thermos)
Eq.13a) Definition of ∆H
ΔHrxn=qrxn/molx
Eq.13b) Functional rearrangement q=∆H*molx
Eq.14a) Definition of S.H.
S.H.=q/(mass*ΔT)
Eq.14b) Functional rearrangement q=mass*SH*∆T
Eq.15) Definition of ∆T
ΔT=(Tfinal-Tinitial)
Sample Questions:
No matter the question, there must be something causing heat loss and something causing
heat gain. Only two types of experiments were done:
○ Two bodies introduced to the calorimeter, one hot the other cold
○ Reactants combined, reaction occurs
Experiment which only heating and cooling happen (no chemical rxns)
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When no chemical reactions are occuring, the question will always give you mass, SH, and ∆T for
one of the bodies, and the other will be missing one of these three. The body for which all three
were given will be called body 'x', and the body for which all but one ws be given will be called
body 'y'.
First, calculate the heat gain/lost by body 'x', using Eq. 14b. Then calculate the heat gained/
lossed by body 'y', using Eq. 12. Now, using Eq. 14b again, rearrange to solve for whatever
variable is being asked for (whichever- m, SH, or ∆T- is missing)
● Experiment which chemical reaction occurs:
When a chemical reaction occurs, the breaking and reforming of bonds can release or
absorb heat from the surroundings. the amount of heat this process uses per mole of a reference
substance is called the enthalpy (Eq. 13a). When a reaction occurs, one of the heat terms in Eq.
12 is always qrxn and the other is always qsoln; the solution is the surrounding material which gains/
loses heat.
Similar to the previous example, in this type of problem, the question will give you enough
information to calculate either
● the heat transfer of either the chemical reaction (qrxn) using Eq. 13b,
● or the heat tranferred to the solution (qsoln) with Eq. 14b.
Based on what's given in the question, one of them will be calculable, and the other will be
missing one variable (note: often molx must be calculated indipendantly, and for the purposes of
this review, is characterized as being 'given' if it can be indipendantly calculated. First, find the heat
transferred in the term that is not missing something by using either Eq. 13b or 14b, then relate the
two terms with Eq. 12, then use either Eq. 13b or 14b to solve for the variable you are looking for.
Solid metal cylinder (given mass, Cp, init T) goes into sealed calorimeter with water (given
volume (mL), and init. T); given final equilibrium T of calorimeter. Find the specific heat of
water.
○ Eq.12 becomes -qmetal=qwater
○ Using Eq. 14b for both terms,
○ qmetal= [m(S.H.)ΔT]metal; and qwater=[m(S.H.)ΔT]water
Combining,
○ [m(S.H.)ΔT]metal=[m(S.H.)ΔT]water
○ (S. H.)water=[m(S.H.)∆T]metal/[m∆T]water
○ mass of water is found with Eq. 1
○ ∆T of both water and metal are found with Eq. 15
Red Flags
· Anytime heat is being released from a reaction, substitute Eq.13 into Eq.12 for qlost, and make
qgained=qsolution and use Eq.14 for that term. So that ΔH=(mCpΔT)solution
· Remember, you may have to use the density calculation (Eq. 1) to get the mass of a body;
also, the mass of solution is the combined masses of solvent and solute, but moles of
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substance x are found either with Eq. 5 or 7b, using the appropriate units!
Lab 8 Emission Spectra
Key Concepts:
● Emission is caused by an energetic excitation of an e-, and upon decaying back to the ground
state, a photon is given off, characteristic to the excitation.
● We looked at a few materials whose emission frequency is in the visible range. Not all
emission is visible, in fact, most of the electromagnetic spectrum is not visible.
● Introduction of Plank's constant (6.626 x 10-34J*S), and Hz (s 1)
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Eq.16)
Eq.17)
Equations
ΔE=hν Energy = Plank’s constant*frequency
νλ=c
Frequency (Hz)*Wavelength (m)= speed of light (m/s)
Sample Questions
Given wavelength (λ), calculate the Energy of the photon.
○ First, Combine equations 16 and 17, then plug in the constants (Speed of light=3 X 108m/s
and h=6.26 X 10-34 Js; these will be give to you. Don’t memorize them)
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Plug and chug.
Understand that anytime you have λ, you have ν, and vice versa by Eq. 17, and with either
you can solve for the energy (Eq. 16).
Red Flags:
Don’t forget about units! The wavelength is often given in nanometers (450 nm). When
plugging into this equation, always use consistent units. Realize that the speed of light is in m/
s, so if you’re using λ, it should be in meters
The Units for frequency are s-1. Don’t be confused with this, and if you want some problems, I
could email you some conversions to do.
The units with these problems are hairy. Be comforble with them.
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Lab 9 (colligative properties)
Key concepts
What are these properties?
Changing the amount of solute in a solution changes the boiling point.
Saturated solutions have different densities based on the soluablility of the solute into the
solvent
Vant ‘Hoff factor, i, is the number of things that are in solution when one solute molecule
dissolves. If NaCl dissolves into Na+ and Cl-, then i=2. If FeCl3 dissolves into Fe+3 and 3Cl-,
then i=4. There are three Chlorides and one Iron (II) ions in the solution.
Molality is introduced
○ Molality is a concentration unit that is independent of volume, so temperature fluctuations
will not affect the concentration unit.
○ Traditional concentration units are conveniently chosen to depend on the volume of the
entire solution (i.e molarity(M)=mol solute/volume solution from Eq. 7a).
○ Molality (m)=mol solute/kg solvent.
○ Know that!
Equations
Eq. 20) Molality (not molarity)
m=molsolute/kgsolvent
Eq. 19) Definition of Boiling point elevation ∆T= BPpure-BPsoln
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(delta T is the difference between the boiling points of the pure solvent and the solution)
Eq. 20) Boiling point elevation/Freezing point depression formula:
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ΔT=mkbi
(when m is the molality, kb is the boiling point elevation constant, and i is the vant 'Hoff Factor.)
Sample questions:
5g of NaCl dissolved in 100mL of water. What is the Molality.
Soln: Using Eq. 20, we see we need molsolute (found by Eq. 5) and kgsolvent (water) found by Eq. 1,
and converting to kg.
Red Flags
● The units are very tricky. Do not lose track of them, it’s the easiest way to lose points.
● Remember notation. m=molality, M=molarity
● This is important. Don’t assume you'll just figure it out.
Lab 10 (VSEPR)
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Key concepts
Vsepr notation (ABE)
Electron Group
Molecular Geometry
Polarity
Equations
● Electron group #= number of things repelling eachother from the central atom
● VSEPR notation (ABNEM)
○ N=number of Atoms attached to the central atom
○ M=number of lone pairs attached to the Central atom only
○ A=central atom
Understand:
Electron Group geometry comes from Electron group # (if the electron group # is 3, the
electron group Geometry is trigonal planar, if EG is 4, it's tetrahedral, every time)
Molecular geometry comes from the VSEPR notation (AB3 is always trigonal planar, but
AB3E is Trigonal Pyramidal)
Understand that sometimes the electron group geom. Is the same as the molecular, and
sometimes (often) it’s different.
Red Flags:
If you cannot tell when you are looking at pictures of molecules, you probably have bigger
problems. This document cannot help you...