acs gen chem 1 final - missed q's/steps Flashcards
(150 cards)
1
Q
how many protons, neutrons, and electrons are there in 69Se2-?
A
protons - atomic #
neutrons - 69-atomic #
electrons - atomic # + 2
= 34, 35, 36
2
Q
which of the following samples contains the greatest # of atoms?
all samples are 1.0g
A
1.0g -> moles of each substance -> atoms
whichever one has greatest is answer, likely substance with greatest molar mass, still check
3
Q
a 1.0g sample of which substance contains the largest # of molecules?
A
smallest molar mass = greatest # of molecules, vice versa
can also go from 1g -> mol -> molecules if needed and makes more sense to check
4
Q
the best name for Cr(SO4)3 is
A
chromium (VI) sulfate
5
Q
magnetite, which has the formula Fe3O4, is comprised of iron (ii) oxide and iron (iii) oxide. what is the ratio of iron (ii) ions to iron (iii) ions in magnetite?
A
dont look at magnetite, just the two ions
iron ii oxide = FeO
iron iii oxide = Fe2O3
1 Fe ion in iron ii
2 Fe ions in iron iii
1:2 ratio
if a Q like this comes up, dont look at product, just ions of reactants
6
Q
an oxide of manganese containing 2.29g of manganese per gram of oxygen. what is the empirical formula of this compound?
A
ignore the per, 2.29g + 1g
3.29g is total
solve as normal
percents -> g -> mole -> divide by lowest -> formula
7
Q
oxalic acid, H2C2O4, reacts with permanganate ion according to the balanced equation above. How many mL of 0.0154M KMnO4 solution are required to react with 25.0mL of 0.0208M H2C2O4
A
recognize that this is a reaction, cant use dilution
mole ratios are not even
take V and M of known solution -> mols known -> mols unknown using mole ratio -> volume unknown using mol/M
8
Q
under which conditions is the solubility of oxygen gas in water the greatest?
A
high pressure, low temperature
think about a soda can, has to be contained = high pressure
wants to be cold = low pressure
not the same as a regular ideal gas, this is in water
9
Q
a heterogenous system is produced when 0.040 moles of solid NaCl is added to 0.10L of 0.10M Pb(NO3)2. which ion is present in the AQ phase at the highest concentration
A
heterogenous = precipitate
add both reactants, balance EQ
identify AQ product
mol of Pb(NO3)2 - > mol of AQ product -> use ratio to determine highest mol of whichever ion
10
Q
what is the oxidation # of Ti in the compound Na2Ti3O7?
A
4 - do right side first, left side second, calculate what is needed to match charge
11
Q
which reaction is spontaneous at all temperatures at standard pressure and concentration?
exo/endo RXN with increase/decrease in entropy?
A
exothermic reaction with an increase in entropy
just remember that spontaneous are exo
12
Q
what frequency of light has a wavelength of 455nm?
A
identify C, wavelength, finding frequency so…
use V=c/A
convert A to m
nm x 10^-9m
be careful of units
13
Q
how many orbitals have the quantum numbers … n = 4, l = 3, ml = 0
A
1
n and l are correct and ml cant be 0
remember that l=3 is f with 7 orbitals
ml = 0 can only be 1 orbital, 1
14
Q
which ionic compound has the smallest lattice energy?
AlN, NaF
A
lattice energy increases with charge
lattice energy decreases as size increases
NaF have a +1 and -1 charge respectively, all other compounds have greater charges
if all charges equal of all compounds, go off of size
15
Q
which property decreases from left to right across the periodic table and increases from top to bottom?
A
atomic radius
16
Q
which of the following statements about pi bonds is false?
pi bonds are stronger than sigma bonds
triple bonds consist of one sigma bond and two pi bonds
etc
A
pi bonds are stronger than sigma bonds
eliminate obvious and remember this
17
Q
what is the shape of the ClF3 molecule?
A
T-shaped
be careful, yes, draw out the molecule
3 bond 2 lone = t-shaped
18
Q
which of the following substances would exhibit dipole-dipole IMF?
A
if asked and needed to answer
draw out each molecule structure
nonpolar = dispersion
polar - dispersion and dipole dipole
determine polarity from molecular shape
ex. NCl3 = 3 bond 1 lone = polar
19
Q
which arrangement has the correct order for decreasing boiling point?
A
high BP = strong IMF = dipole dipole strongest = most polar highest
larger the molecule = stronger dispersion forces
small molecule w biggest difference in EN is largest, following by decreasing
largest molecule has smallest boiling point
evaluate all molecules, if decreasing choose smallest most polar, then to biggest molecule
20
Q
which of the following would likely have the lowest boiling point?
A
draw out all lewis dots
dipole dipole = high boiling
whichever molecule is non-polar = dispersion = lowest boiling
21
Q
which of the following substances has london dispersion forces as the only intermolecular force?
A
draw out all molecules
whichever molecule is non polar = only dispersion = answer
remember polarity from geometry or just looking at the structure
22
Q
the viscosity of liquids increase as…
A
think about syrup or honey
low temperature, high IMF
23
Q
which substance boils at the highest temperature?
A
another boiling point Q
draw out all structures, determine dipole-dipole, theres your answer
if two dipole-dipole, count electrons, most electrons wins
24
Q
what is the normal freezing point for the substance in the phase diagram?
A
evaluate phase diagram
normal = 1atm
go from 1 atm on the left side until you hit line, go down, theres your temp
25
molecules will be nonpolar if...
1st. the molecular shape around the central atom has no lone pairs, if it does it has to be either square planar (6, 4, 2) or linear
2. all atoms around the central atom are the same
26
Planks constant is 6.626x10^-34Js, what is the value in kJms?
Jxs -> kJ (1/1000) -> ms (1/10^-6)
27
what is the reading on the graduated cylinder to the right?
only estimate 1 sig fig, no more.
If it is from 40 to 50 and the reading is between 42 and 43, it is 42.5, not 42.50
28
what is the formula of iodic acid?
HIO3
29
the density of helium is 0.164kg/m3. what is the density in lb/ft3?
kg -> lb then 1m/3.28^3
in general, just watch units
look at starting and where you are trying to get to
30
what is the correct name for N2O5?
dinitrogen pentoxide
31
what is the formula for hydroiodic acid?
HI
32
using the models of particles below, which are isotopes of the same element?
evaluate all diagrams
isotopes = differing neutrons
SAME element = same electrons and protons
select answer this way
33
chlorine occurs naturally as a mixture of two isotopes with atomic masses of 34.97 and 36.97. what are the relative abundances?
%Cl37 = (average atomic mass Cl - mass 35Cl / mass 37Cl - mass 35Cl)
using this percentage, you can then subtract it from 100 and find the percentage of 35Cl
essentially atomic mass - mass of the lowered # isotope, divided by the mass of the higher number - mass of lower number
MM-2ndisotope / 1st isotope - 2nd isotope
34
the element thallium, Tl, has two stable isotopes, 203Tl and 205Tl. which statement correctly describes the relationship between the relative abundances?
find molar mass of Tl, whichever isotope it is closest to will have greater abundance
hence, % abundance of 203Tl < % abundance of 205Tl
35
if the formula of an ionic oxide of an element X is X2O3, what is the formula of the chloride of X?
Knowing that X has a +3 charge, when combining it with Cl which has a -1 charge, it is XCl3
36
in all neutral atoms there are equal numbers of?
protons and electrons
37
Bromine has two naturally occurring isotopes. The most abundant isotope 50.69% is 79Br35 with a mass of 78l.913 amu. What is the other isotope?
Finding mass from relative abundance
For this question set the average molar mass of bromine equal to the molar masses of each isotope multiplied by their respective percentages
Find the percentage of the other isotope by subtracting 50.69 from 100
Turn the percentages into decimals
and solve like this
molar mass = (mm1st)(%1st) + (Xmm)(%2nd)
rearrange and solve for the second molar mass
38
Lithium has two naturally occurring isotopes, 6Li and 7Li, with masses of 6.015 amu and 7.016 amu respectively. what are the relative abundances?
finding relative abundance from mass
for this question, will want to set the % abundance of the lower isotope as X and the higher isotope to 1-x
From here find the molar mass and make it equal to the molar masses of the isotopes times x or 1-x respectively
MM = (1stisotopeMM)(x) + (2ndisotopMM)(1-x)
rearrange and solve for x, then subtract from 100 to give you the other percentage
39
which group contains nonmetals, metalloids, and metals?
group 15
40
the halogens are found in group?
17
41
alkaline earth metals form what charge?
+2 ions/charge
42
what is the wavelength of light (in nm) produced by the electronic transition between levels 4 and 2 of a hydrogen atom?
this is a rydberg EQ problem
2.18x10^-18 (1/4^2 - 1/2^2)
using this energy, can solve for wavelength using E=hc/A
rearrange and you get A=hc/E
plug and solve, convert m to nm by dividing by 10^-9.
rydberg eq = 2.18x10^-18 (1/ni^2 - 1/nf^2)
43
what is the ground state electron configuration for Zr2+?
(Kr)4d2
44
what is the energy of a photon with a wavelength of 656nm?
being asked energy of a photon and given wavelength, we want to use E=hc/A
h=6.626x10^-35
c=2.998x10^8
watch units, convert nm to m by multiplying by 10^-9
45
when excited, a sodium atom emits a photon of frequency 5.090 x 10^14 s-1. what is the energy associated with this emission?
use E=hv, plug and solve
46
which electron transition in a hydrogen atom is associated with the largest emission energy?
know that emission is going down, eliminate answers off that, and then know that the lower transition states release higher energy
calculate using rydberg if needed
47
which emission line in the hydrogen spectrum occurs at the highest frequency?
emission is going down, eliminate answers off that
know that lower transition states also occur at a higher frequency, answer off of that
at lower n values higher energy is released
calculate if needed
48
the picture at the right is an early model for the atom. this model differs from the current model because in the current model?
eliminate obvious answers
for this specifically know that electrons no longer move in orbits in the current model
49
what is the ground state electron configuration for the manganese atom? (Mn)
1s2 2s2 2p6 3s2 3p6 3d5 4s2
be careful with acs, the d may come before the 4
regardless if written out correctly, should be able to find the answer
50
what is the maximum number of electrons that can occupy an orbital labeled dxy?
regardless of the label of the orbital, according to pauli acclusion only 2 electrons can fill an orbital, regardless of its label
so the answer is always 2
51
which of these species is/are paramagnetic?
write out electron config for each one
whichever one has unpaired and unfilled is paramagnetic
be careful with writing out configs
52
the radii of the ions in this series decrease because
for this question, the radii decreases because the effective nuclear charge is increasing
know that increase of Zeff = decrease in ionic radii
and vice-versa
53
which of these atoms will be the smallest?
follow trend of atomic radius if all atoms are neutral
if ions, follow trend of ionic radius using knowledge of Zeff, charge, etc
54
the species F-, Mg+, Na+ all have the same number of electrons. which is the predicted order when they are arranged in order of decreasing size?
F>Na>Mg
for this question, with all having the same # of electrons, atomic radius is irrelevant here
refer to trend of ionic radius and knowing that the increase of Zeff and increase of protons = a decrease of ionic radius, vice versa
Here, F has the least number of protons and is lowest in Zeff, meaning it has the greatest size and vice versa
55
which ion is the smallest?
Na+
Al3+
if all are the same in terms of electrons, have to look at ionic radii trend
know that an increase in protons and Zeff means a decrease in ionic radii
choose the option with the most electrons and greatest Zeff
56
which ion has the largest radius?
K+
Cl-
again, an ionic radii question
while all options may not have the same electrons, in them being ions it is still an ionic radii Q.
know that an increase in protons and Zeff means a decrease in size
eliminate answers down to the ions with the least protons and Zeff, meaning the greatest radius
57
which pair of elements is listed in order of decreasing first ionization energy?
Na, Mg
Mg, Al
a trickier question
since not asked directly for the trend in ionization energy, and given that all of the options are in the same period
there is an exception
have to write out all configs, determine the pair that has a config that is paired, half or full, and the config that is unpaired
this will give you a decrease in first ionization energy
if asked oppositely, look for an element with a unpaired config and an element with a paired config
58
when the species F-, Na+, and Ne are arranged in order of increasing energy for the removal of an electron, what is the correct order?
F-
know that the question is referring to IE
notice that not all elements are neutral, meaning that you cannot use the trend for IE
instead, look at the charges and know that an ion with a (-) charge will allow for an easier removal, hence lower energy. (-) charged species have an excess of electrons, making it easy = lower energy
that know it will be harder to pull electrons from a + charged species, giving off more energy. (+) charged species are already at a deficit for electrons, making it harder = more energy
59
what is the wavelength of a photon with an energy of 6.51x10^-9?
use E=hc/A
rearrange for A=hc/E
convert from m to nm by dividing by 10^-9
plug and solve
60
an atom of Fe has two 4s electrons and 6 4d electrons. How many unpaired electrons would there be in an Fe2+ ion?
write electron configs for both
know that the removal or addition of electrons must be to the highest orbital
remove/add electrons as needed, removing only from the highest n #
61
what mass of carbon is present in 1.4x10^20 molecules of sucrose (C12H22O11)?
molecules -> mol using avid# -> mol of C using mole ratio -> mass of C using molar mass
sometimes you dont always need all the information provided, such as the molar mass of sucrose, be weary of this
62
a 4.08g sample of a compound of nitrogen and oxygen contains 3.02g of oxygen. what is the empirical formula?
g -> mol using molar masses -> divide by lowest mol amount -> turn into whole coefficients
63
ibuprofen, a common pain reliever, contains 75.7g carbon, 15.5g oxygen, and 8.80g hydrogen by mass. what is the empirical formula?
g -> mol using molar masses -> divide by lowest mol amount -> turn into whole # coefficients
64
which sample has the largest mass?
this question asked about numerous samples that were all 1 mol
if asked this q know that 1 mol of atoms/molecules is extremely small
in knowing this, the correct answer is 1 mol of the physical object or substance, not atoms or molecules
65
a 10 gram sample of which substance contains the greatest number of hydrogen atoms?
g -> mole of compound -> mol of H -> molecules
do this for all compounds to find the greatest one
66
a 25.0g of carbon dioxide contains X oxygen atoms
g -> mol Co2 -> mol of C using mole ratio -> atoms using avid#
67
a sample of a compound of xenon and fluorine contains molecules of a single type; XeFn, where n is a whole number. If 9.03x10^20 of these XeF molecules have a mass of 0.311g, what is the value of n?
XeF molecules -> mols of XeF
use the given grams and divide by the mols of XeF to find the molar mass
set molar mass of XeF = molar mass of Xe + molar mass of F(n)
solve for n
a bit of a trickier question, but first find molar mass using molecules -> mols and the given grams
then set this value equal to the molar masses of Xe and F respectively, with a variable tied to F
68
a 3.41x10^-6 g sample is known to contain 4.67x10^16 molecules. what is the compound?
molecules -> mols
use given grams and divide by the mols to get molar mass
match the molar mass up with the compound that also has the same molar mass
69
how many sodium ions are in 25.0g of Na2Co3
g -> mol -> mol of Na using mol ratio -> ions of Na using avid#
ions, molecules, atoms, all the same using avogadros #
70
a sample of ethanol (C2H6O) contains 3.024g of hydrogen. how many moles of carbon are in the sample?
g -> mol hydrogen -> mols of C using mole ratio of ethanol
71
a 10.000g sample of water contains 11.19% H by mass. What would be the % of H in a 20.000g sample of water?
know that % composition does not change regardless of the sample
if the composition stays the same, the % composition will stay the same regardless of the sample size or conditions
hence, it remains the same
72
what is the empirical formula of a compound of carbon, hydrogen, and oxygen that contains 51.56% carbon and 14.09%
first, change the %s to grams
g of element -> mol -> divide by lowest # -> turn into whole # coefficients
73
THC, the active agent in marijuana, contains 80.16% carbon, 9.63% hydrogen, and 10.17% oxygen by mass. what is the empirical formula?
again, change the percentages to grams
g of element -> mols -> divide by lowest amount -> turn into whole # coefficients
74
what is the empirical formula for a compound that is comprised of 54.0% Na, 8.50% B, 37.5% O?
again, same process
change percentages to g
g of each element -> respective mols -> divide by lowest amount -> turn into whole # coefficients
75
a molecular compound is found to consist of 30.4% nitrogen and 69.6% oxygen. if the molecule contains 2 atoms of nitrogen, what is the molar mass of the molecular?
g of each element -> mols -> divide by lowest number -> turn into coefficients
find the empirical formula for NO, then considering that there are 2 mols, make N=2 and multiple O by 2.
Knowing this formula now, solve for molar mass by referring to periodic table
76
what is the theoretical yield of No that can be produced from the reaction of 3.50 mol NH3 and 4.01 mol O2
solve for LR, mol of each reaction to mols of product
the least mol product = limiting reaction = theoretical yield
77
what is the mass of TiO2 found when 0.476g TiCl4 are reacted with 0.501g H2O?
find LR then go from given g of LR -> mol of TiO2 -> g of TiO2
78
an initial mixture of N2 and H2 is shown to the right? which representation shows what would be present after the reaction is complete?
assess original image and how many molecules there are for each reactant
find the excess reaction by going from molecules of each reactant -> molecules of the compound
in identifying the excess reactant, eliminate all obvious options.
usually can solve just by determining excess. if not, assess the product and how many molecules there should be
79
a 2.32g sample of Na2So4 x nH2O yields 1.42g Na2SO4 upon reacting. What is the value of n?
subtract the given mass of Na2So4 from the given mass of the total, giving you the mass of nH2O.
from here, determine the mols of H2O present
determine the mols present of the given Na2SO4, then solve as you would an empirical formula Q, giving you n of H2O
80
Equimolar amounts of nitrogen, hydrogen, and argon are placed in a reaction chamber. which substance will determine the amount of ammonia produced in the reaction below if the reaction goes to completion?
for this Q, just use the formula and find the LR
mol of both reactants -> mol of product using mole ratio of equation
the lesser produced = LR = only substance to determine the amount produced
81
how many total molecules will be present when the reaction of 5,000 molecules of CS2 with 15,000 molecules of O2 gas goes to completion?
molecules given of reactant 1 -> molecules of product
molecules given of reactant 2 -> molecules of product
add together
instead of using avogadros number for this, just use mole ratios to find molecules of product from both reactants, then add
82
what amount of excess reagent remains when 0.30 mol NH3 reacts with 0.40 mol O2 to produce NO and H2O?
determine LR and ER
mol of LR -> mol of ER -> substract this solved mol of ER from the given amount of ER
83
what amount of excess reagent remains when 0.500 mol Li reacts with 0.350 mol N2?
find LR and ER
given mol of LR -> mol of ER
subtract from given = remains
84
the combustion of C3H8O with O2 is represented by this eq
when 3.000g C3H8O and 7.38g O2 are combined, what is the excess reagent and how many moles of that reagent remain?
find LR and ER
same process
g LR -> mol LR -> mol ER -> mass of ER
subtract mass of ER from mass of given
convert back to mol
85
consider this reaction for the production of lead
what is the theoretical yield of lead that can be obtained by the reaction of 57.33 PbO and 33.80g PbS?
determine LR and ER normal way
g -> mol -> mol of product
the lesser amount = LR
mol of LR produced -> g of product = theoretical yield
86
what amount of excess reagent remains when 4.0g zinc reacts with 2.0g of phosphorus?
determine LR and ER
g -> mol -> mol of product
from here go from g of LR -> mol of ER -> g of ER
subtract g of ER from given
87
an initial reaction mixture of O2 and F2 is shown. which representation shows what would be present after the reaction is complete?
again, count up all of the molecules present in the initial picture
determine LR and ER by going from molecules -> molecules of product
in knowing the excess now, should be able to eliminate all obvious and get the answer this way
if not, evaluate the product and how the product should look in comparison
88
which compound is a weak electrolyte when dissolved in water?
know that bases or weak acids are weak electrolytes, in this Q the answer is NH3 which is a base
try and remember strong acids and bases, with Qs asking about electrolytes should be able to determine knowing this relationship
89
the figure shows a particular representation of the resultant solution and solid product after AQ calcium chloride and AQ silver nitrate react. what species is/are present in excess?
write out the EQ for the two reactants
circle the molecules of product in the image, whatever is leftover in the AQ phase is excess
90
what is the net ionic equation for the reaction between Na2S and Pb(NO3)2?
remember difference between net and total
net is the fully reduced, all spectator ions eliminated reaction
remember solubility rules as well
S2- + Pb2+ -> PbS
91
for this reaction, what are the oxidizing and reducing agents?
2AuCl3 + 3H2 -> 2Au + 6HCl
count all oxidation numbers for each molecule
remember oxidation rules
OIL RIG
from here, we can determine that Au GAINS electrons, meaning it is the oxidizing agent
conversely, H2 LOSES electron, meaning it is the reducing agent
92
what is the molar concentration of a solution made by dissolving 8.58g of sodium acetate in water and diluting to 750.0mL?
g of sodium acetate -> mol of sodium acetate
M=mol/L
solve for molarity as normal
93
what is the concentration of the bromide ion if 25.0mL of a 0.50M AlBr3 solution combines with 40.0mL of a 0.35M NaBr solution. assume volumes are additive
here we need to setup 2 equations
NaBr -> Na+ and Br-
AlBr3 -> Al3+ and 3Br-
these two equations need to be setup in order to determine the total amount of Br ion
go from given volumes of each --> L -> mol of compound (multiplying by given molarity) -> mol of Br ion using mole ratio
now knowing the mols of the Br ions in each EQ, add them together and divide by the total amount of volume used
this will give you the concentration of the bromide ion or particular ion
94
a solution is made by dissolving 60g of NaOH in enough distilled water to make 300mL of a stock solution. what volumes of this solution and distilled water, when mixed, will result in approximately 1M NaOH?
first go from g NaOH -> mol and then divide by L to give you molarity of NaOH
in assessing all of the given options, use the dilution EQ to find the proper match
M(X) = (1)(x)
the x on the right side with the one will be the total. subtract the stock amount from the total and if it matches the distilled amount, that is your answer
95
what is the molar concentration when 7.00mL of a 3.25M aq solution is distilled to 25.00mL
dilution problem given no reaction
first convert mL to L
use M1V1=M2V2
rearrange to solve for M2
96
what volume in mL of 0.0557 M Sr(OH)2 is needed to neutralize 36.4mL of a 0.0750M HNO3 solution?
if not already a balanced EQ, write out a balanced EQ
determine the mols of HNO3 using molarity and liters
mol HNO3 -> mol of Sr(OH)2
use the mols of Sr(OH)2 and divide by molarity to get volume in L
convert to mL
97
when 1.0M aq solution of KI, NaC2H3O2, and Pb(NO3)2 are mixed together, what precipitate forms?
evaluate all options knowing solubility rules
eliminate obvious
whatever option is insoluble, no need to write out balanced EQ
98
what is/are the spectator ions in this reaction?
HC3H2O2 + NaOH -> NaC2H3O2 + H2O
determine total and net ionic equations
whatever ions are present on both sides of the equation are the spectator ions
remember solubility and go with your gut
Na+ is present on both sides, so it is Na only
be careful with molecules like HC3H2O2, this molecule cannot be broken up
all other reactants and products are unique, Na being the only one on both sides
99
which molecular equation would give this net ionic equation?
H+ + OH- -> H2O?
with all equations given, write out total and net ionic equations
whichever one matches is the one that is correct
eliminate obvious one that dont even include H or OH
trust your gut, remember solubility and charges, subscripts, etc
100
what is a weak acid in water?
HBr
HF
just something you have to remember, HBr is a strong acid, eliminate all obvious in Qs like this
hence, HF is the answer
all other answers will likely be strong acids or bases
101
what particles would be present in NH3?
eliminate all obvious answers with a question like this, know that NH3 is a weak base so it does dissociate partly
should be able to determine answer logically by eliminating all others
102
one-gram sample of carbon and copper, originally at room temperature, reach equilibrium after being placed in 200mL of boiling water. Which statement is correct?
carbon = 0.709
copper = 0.385
a q and relationship you just have to remember
in viewing the specific heats, we can see that copper have a lower specific heat, meaning that it will absorb less energy or does not need to absorb as much energy as carbon in order to reach equilibrium.
reach equilibrium = same temperature in the end
hence,
copper would absorb less energy than carbon and attain the same final temperature
103
a 10.0g sample of silver is heated to 100C and then added to 20.0g of water at 23.0C in the insulated calorimeter. At thermal equilibrium, the temperature of the system was measured at 25C. what is the specific heat of silver?
remember the following Eq when dealing with dual temp change
ChotMhotThot = -CcoldMcoldTcold
in knowing this formula, we can rearrange for Chot or the specific heat of Ag
Chot = -CcoldMwaterTwater/MhotThot
plug and solve, be careful of all units
104
what mass of benzene C6H6 must be burned in a bomb calorimeter to raise its temperature by 15C
H = -41.9kJ
C = 1.59kj/C
knowing the formula q=mcAT
we can solve for m by rearranging and knowing all other values
m=q/CAT
watch units, check yourself
105
what is the enthalpy of formation for HF?
2HF-> H2+F2
in just looking at this equation, given that the product has the coefficient of 2, we want to reduce HF to its most standard form
by dividing HF by 2, we get HF, but what we do to HF we also have to do to the reactants side,
hence,
= 1/2(rxn)
106
if a systems internal energy increases by 250kj after the addition of 375kj of energy as heat, what was the value of work in the process?
remember E=w+q
set E = 250
set q = 375
solve for w
hence, = -125
107
two metal samples of the same mass and initially at 25C, are treated so that each metal receives the same thermal energy. which metal will have the highest final temperature?
X=0.350
Z=0.895
be weary of this Q, and read carefully
in reading that both metals will receive the same thermal energy, we can examine the specific heats of both metals
in seeing that X has a lower specific heat, if both receive the same thermal energy we know that X will be at a higher temperature than Z, given that it takes less energy to reach a higher temperature
108
a piece of iron is heated to 95C and then placed in an insulated vessel containing 250g of water at 25. when the system comes to equilibrium the temperature of the system is 35C. what is the mass in g of iron?
iron = 0.450
water - 4.184
another problem with deal substances and duel temps
use mhotchotThot=-ccoldmcoldTcold
rearrange for mhot
mhot = -mwatercwaterTwater/chotThot
for temperature, we want to use the final temperature for both substances, subtract their initial temps from the final
plug and solve, water units
109
when a 45.0g sample of an alloy at 100C is dropped into 100g of water at 25C, the final temperature is 37.0C what is the specific heat of the alloy?
again, we want to use the following formula
mhotchotThot=-ccoldmcoldTcold
rearrange for chot
chot = -ccoldmcoltTcold/mhotThot
for temperature, we want to use the final temperature for both substances, subtract their initial temps from the final
110
when 68.00J of energy are added to a sample of gallium, that is initially 25C, the temperature rises to 38.0. what is the volume of the sample?
c=0.372
D=5.904
in being asked for volume and being given density, we want to solve for mass
since there is no dual temp change, use q=mcat
rearrange for m and you get
m=q/CAT
plug in and solve for m
now rearrange D=m/V
and you get V=m/D
plug and solve, watch all units
111
a student mixes 100mL of 0.50M NaOH with 100mL of 0.50M HCl in a styrofoam cup and observes a temperature increase of T1. When she repeats the experiment using 200mL of each solution, she observes a temperature change of T2. if no heat is lost to the surrounding or absorbed by the sytrofoam cup, what is the relationship between T1 and T2?
keep in mind q=mCAT
the only way for the change in temperature to change is if the masses of actual substances were to change
regardless of the addition of more volume, the specific heats still remain the same and the temperature changes still remain the same
so
T1=T2
just something you have to remember. unless it is a direct factor being changed, it is the same. think logically, you got this
112
a 100g sample of NH4NO3 is decomposed in a bomb calorimeter. the temperature increases by 6.12C. what is the molar heat of decomposition of NH4NO3?
c=1.23
NH4NO3 = 80.0g
in seeing no dual temp change, we want to use q=mcat
plug in all given values to solve for Q
once having solved for Q, we want to multiply the molar mass by this value
this will ultimately give up
kj/mol, which is the desired units and value we want
anytime the question is asking for heat, solve for q
since it is asking for molar heat, we want to find kj/mol
we can do so by multiplying by the given molar mass
a trickier question at first, but just read through, look at units, where you are trying to get to, and solve
113
given these values of H in the table, what is the value of H for the reaction?
CS2+6H2O2->CO2+6H2O+2SO2
CS2+3O2->CO2+2SO2 = -1077
H2+O2->H2O2 = -188
H2+1/2O2->H2O = -286
read through the problem carefully, be weary of states, solve as you know
for the second EQ we want to flip the equation and multiple by 6 to get 6H2O2 on the reactant side
for the third EQ we want to multiply by 6 to get 6H2O on the product side
the first EQ goes unchanged
write out all EQs and cancelled as needed
total kj added up is -1665
be careful, double check these kinds of problems, dont second guess, you got this
114
what is the order of ScN, MgO, CuCl2, and NaBr in order of increasing lattice energy?
remember that an increase in charge = an increase in lattice
also remember that an increase in size = a decrease in lattice
in knowing these two things, count the charges of all of the compounds
in seeing that not all compounds are equivalent in charge, we then should rank them in order of lowest to greatest charge
we find that...
NaBr
115
what is the formal charge of the nitrogen atom in nitric acid, HNO3?
this is a special one, unfamiliar to most
the H is detached from the N and instead bonded to the O, think about hydrogen bonding
so in knowing this, and distributing out all electrons,
we count that N has 4 bonds in the lewis dot structure and know that it originally came with 5 valence electrons
5-4 = +1 = the correct formal charge
solve how you normally would, but keep molecules like this in mind, if it has an O,H, and an additional atom, the H is likely bonded to one of the Os
116
using the bond energies, what is the Hrxn for the reaction below?
for questions like this, we want to remember that the product side should be negative and the reactant side should be positive
opposite to what an enthalpy of formation Q is sort of like
in knowing this, add up all of the bond energies from the table given for the product, and put a negative sign with it
add up all of the bond energies for the reactants side, making it positive
we can then add the two together to get the total Hrxn
a bit of a trickier Q, but just remember this relationship
117
which molecule is nonpolar but contains polar bonds?
just draw out all molecules, be careful
whatever molecule has no lone pairs is nonpolar
polar bonds = difference in EN between the two elements
first eliminate options based off of that, then draw out each structures
remember that all molecules are nonpolar unless they have lone pairs
those with lone pairs that are nonpolar are square planar (4,2) and linear
additionally all lewis structures with the same element entirely around the outside will denote it as polar having following the first exception
so Co2 is the correct answer
118
The molecular orbital He22+ and He2 are shown here. what are the bond orders of He22+ and He2?
here, you want to count up the number of bonding and antibonding electrons
keep in mind that a filled orbital = 2 electrons
in knowing that each orbital and whether it is bonding or antibonding, we can count up each
the formula for bond order is 1/2(bonding-antibonding)
in solving this particular Q we get 1 for He22+ and 0 for He2
119
arrange CsBr, NaCl, and RbBr in increasing magnitude of lattice energy
remember that an increase in charge = an increase in lattice energy
also remember that size increasing = lattice energy decreasing
determine whether or not all answer options are equal in charge
for this particular Q, we see that all answer Qs are indeed equal in charge
so for this, we want to evaluate what molecules are the smallest and biggest, looking at the first ones in each compound
Cs is the biggest meaning it has the smallest energy, being the lowest in the group, Rb next, and Na being the smallest meaning it has the greatest lattice energy
hence,
CsBr
120
how many covalent bonds are represented in the formula NH4Cl?
this question is a little trickier
just have to remember and be on the lookout for things like this
in remembering that NH4 is positively charged, we know that NH4 and Cl are being held together by their charges, since they are ions = ionic bond between them
even though it is not a nonmetal and metal attraction, this ionic charge is not a covalent bond
this eliminates there being a covalent bond between the N and the Cl
so now counting up the covalent bonds present, which are bonds between a nonmetal and nonmetal, we count up 4, all 4 being from the N to the 4 Hs
a little trickier question yes, eliminate the obvious and factor in charges and everything else as needed. remember your definitions of covalent and ionic bonding.
sort of remember that ions = ionic even though that does not apply entirely
121
the resonance structure for benzene indicates that
assess all of the structures and eliminate the obvious
for this, you will just have to remember that the bonds between carbons in benzene are identical
or for another problem, just have to remember that the bonds are identical
while you have been taught that resonance is unique, just remember that the bonding is identical
resonance is just the change in locations of electrons, the bonding and locations of the atoms are all identical
just have to remember this concept
122
what is the bond order of the C-O bond in the acetate ion?
count all bonds as singular
so for this particular question, we want to look at all of the C-O bonds formed
we count up that there is one singular bond and one double bond, but we count this as 2
now knowing this, for the bond order of molecules we want to use the #bonds/#of domains
with there being only 2 domains, we do 3/2 which gives us 1.5
for this type of eq, assess all of the bonds that the question is asking, remember to count up all bonds, then just divide by the # of domains
123
the lewis dot structure of ethanol is given below. estimate the enthalpy of combustion of ethanol using the bond enthalpies in the table
again similar process as before
we want to count up all of the bonds and multiply by the coefficient in the balanced Eq if there is one, consider all subscripts and coefficients
reactant - product will get you the answer
for these particular Q's, just remember to subtract using the product, or if adding, make the product negative
124
for the nitrate ion, NO3-, predict the bond energy between nitrogen and the oxygen labeled A
here is a trickier question
use the bond energies given and add them all up together across all resonance structures
now divide this total amount of energy by the amount of resonance structures and you will get the average bond energy between N and O.
a trickier Q, but if asked about bond energy given resonance, remember to add up all totals then divide by resonance structures
125
what is the molecular geometry around the N in the molecule depicted?
remember and memorize your geometries
for this particular question, the N in the diagram is without its lone pair
for questions like this add up the electrons across the entire molecular and double check the image
for this Q as mention, the N actually has a lone pair, making the geometry 3 bonds with 1 lone = trigonal pyramidal
126
according to vsepr, what are the approximate values of the bond angles X and Y?
for these particular questions, try not to determine the angles off of the picture more than you would the actual structure
remember structures and their angles and then determine the answer off of that
for this particular q, y is 120 because the structure is trigonal planar, and X is 109.5 because the structure is tetrahedral
127
SCl2 has _ bonds and the overall molecule is _
polar or nonpolar?
draw out the lewis structure and be careful
just from the lewis structure we see that S has two lone pairs, meaning that it cant be nonpolar
now looking at all of the elements, we see that there is a different in electronegativity between S and Cl, making the bonds also polar
128
what are the polarities of the indicated molecules?
again for a question like this, draw out all structures as needed and be careful
in remembering your rules for polarity, we know that square planar and linear are nonpolar, and that helps us solve this question
129
which best illustrates a pi bond?
for this particular question, evaluate all images and eliminate the obvious
we know that sigma bonds possess overlap, so we can eliminate all images with overlap
that will leaves us with the correct answer of orbitals that are not overlapping
130
what is the hybridization of the indicated molecule?
remember your rules for sp and that sp is sigma-pi
in counting the bonds, remember that all bonds have single bonds, double bonds have 1pi and triple bond have 2 pi. remember also that all bonds create sigma bonds
remember also that lone pairs count as sigma pairs
131
how many sigma and pi bonds are in the molecule below?
count up as you normally would, eliminating all obvious answers
evaluate and consider all molecules, if they have a subscript remember that those also count as bonds as well
132
according to MO theory, f2 would?
mo diagram shown
in answering a question with an MO diagram, we need to remember the labels
the order from top to bottom is
anti
anti
bond
bond
anti
bond
anti
bond
this will allow us to count up the number of bonding and antibonds, determining the bond order
additionally we can answer the question on whether or not it is paramagnetic or diamagnetic by looking at the filled or unfilled orbitals
in filling out an MO diagram, we want to add up based on the atomic number
F2= 9x2=18
fill in the diagram as you normally would, solve for bond order and determine spin
remember that each orbital counts as 2 electrons
133
using the mo diagram given to the right, what is the bond order for N2-?
again, remember the order for bond and anti bonding for a MO diagram
use the atomic number and fill in the MO diagram as normal from bottom to top
calculate bond order as you normally would using
1/2(bond-anti)
134
a gas behaves most ideally at
low pressure and high temperature
this one is simpler, just think about has gasses behave and the properties of gasses
not the same as solubility
135
what is the density of Xe gas at 70C and 2.50atm?
for this equation, we want to use PV=nRT
since we arent given the mols of Xe, we can just assume it as 1
we first want to also turn C into kelvin
now we can rearrange for V
v=nRT/P
once having solved for V
find the molar mass of Xe and divide by the solved L to get density
136
a 10.0L sample of an ideal gas at 25.0C is heated at constant pressure until the volume has doubled. what is the final temperature?
for Q's like this we want to be on the lookout for any constant variables and just use the ones we are given in an Eq, since we are not given a particular gas here, since we are not given a particular gas or element, we want to just assess the variable given
we are given V, P constant), and T
PV=nRT
in rearranging this eq to only give us V,L, and T
we find that PV/T
given that pressure is also constant, we can cancel this out
so we are left with v/T
rearrange and solve for the final T
T=V2T1/V1
convert all C to K, plug and solve
137
what volume of CO2, measured at 0.993atm and 28C, must react in order to completely consume 59.0g of Al2O3
balanced eq given
here is a problem where we have to do stoic as well as the ideal gas law eq
knowing that we want to solve for volume of CO2, we can first solve for mols of CO2
using the balanced eq we can go from g of Al2O3->molAl2O3->mol CO2 using mole ratio
now knowing the mols of CO2, we can setup the ideal gas law Q to solve for volume
V=nrt/P
convert all C to K, plug and solve
138
if the diagram shown is representative of particles in a sample of ideal gases, which statement is true?
B has the largest partial pressure
ok, so for this type of question we want to assess all of the options and which option has the largest amount of molecules
the option with the largest amount of molecules present will also have the largest/greatest partial pressure and vice versa
this is just something youll need to remember if asked about partial pressure given a diagram
139
the graph to the right represents four different gasses at the same temperature, which are the correct labels for the curves?
with a graph question like this, really read the question
it states that all are at the same temperature, and knowing your relationship with speed and molecules, you know that the only other factor would be amount/weight, or molar mass
so here you just want to determine that the elements with the greatest molar masses will be the slowest, and those with the lowest molar masses will be the fastest
you can answer this type of question by matching those answers
140
what is the correct order of increasing boiling point in NaCl, Br2, and ICl
here youll want to draw out each lewis structure as needed
know that nonpolar=dispersion which is low
know that polar = dipole-dipole and dispersion which is higher
and know that anything ionic, a compound held together by ions will be the largest
from here and knowing that the greater the IMF the greater the boiling point, you can determine the order
141
a pure substance is initially at 365K and 545 torr. what happens to the substance when the pressure is increased at 760 torr at constant temp?
here you will want to read the diagram carefully and the units given in the problem carefully
remember each sections of a phase diagram and the changes between them
in knowing the initial values, you know that you start as a gas and in increasing pressure, you then fall into the liquid range
this is condensation
142
which sample deviates most from ideal gas behavior?
read the question, know that deviates means different
know that ideal gas is high temp and low pressure
eliminate all obvious
the answer should be somewhat apparent
143
what happens to the volume of a fixed amount of gas if both the pressure and absolute temp are doubled?
for questions like this we want to look at pv=nrt
in doubling the pressure, the volume will double, but in doubling the temperature as well, the volume will then by reduced by 2
so it stays the same
know that variables together are impacted directly and those on the opposite side of the equals sign are indirect
144
what mass of solid aluminum is needed to react with excess H2SO4 to produce 20.0L of H2 at 1.0atm and 298K?
balanced EQ given
here we first want to solve for the mols of H2 because we have enough information to do so
we can setup the equation as n=RT/PV
convert all C to K as necessary, remember the gas constant to be 0.0821
after having solved for n of H2, we can convert to mols of Al using the balanced EQ and then convert to g using the molar mass
this will give us the mass of Al
145
what is the percent yield when 1.72g of H2O decomposes and produces 375mL of O2 measured at 42C and 1.52atm
balanced EQ given
a bit of a trickier Q
remember that % yield if actual/given divided by theoretical A/T
we first want to convert g of H2O -> mol
now we can go from mol H2O -> mol O2
now we can go to mol O2 -> g O2
this value is our theoretical yield
our actual yield can be calculated using pv=nrt and solving for n
convert mL and C as needed and solve for n=RT/PV
finally convert to g using molar mass
this is the actual yield, now we can solve for percent yield by A/T x100
146
suppose a gas contains equal moles of He and O2. Which is true?
the partial pressure of each gas is the same
yes, this is something you just have to remember
if the mols are equal then despite the compositions the partial pressures will be the same
147
a mixture of 3.25 moles of oxygen and 2.75 mols of nitrogen gas exert a total pressure of 22.4 atom. what is the partial pressure of oxygen?
to solve for partial pressure, we will want to multiply the mole fractions of each element by the total pressure
we can do this by adding up both mols and getting the total mols, then dividing each given amount by the total
multiple the respective mol fractions by the total partial pressure and you will get the partial pressure of the particular element
Pp=mole fraction x Ptot
148
under the same conditions of temperature and pressure, H2 diffuses __ than O2
for this question, remember the rate of diffusion EQ
H2/O2 = the square root of O2/H2
invert the two
now you can solve for the rate, which is 4 times faster in this case
149
why is the boiling point of Br2 higher than Cl2?
Br2 is polarizable and therefore has greater dispersion forces
eliminate all obvious and come down to the answer that is actually true
this answer is unfamiliar to you, but should be able to limit down to an answer just by eliminating obvious ones and knowing your relationship of boiling point and IMF
150
which substance has the lowest vapor pressure at 25C?
for vapor pressure, just remember that an increase in IMF = a decrease in vapor pressure
here H2O has the greatest IMF being polar, which means it also has the lowest vapor pressure
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