acs gen chem 1 final - missed q's/steps

Question 1

how many protons, neutrons, and electrons are there in 69Se2-?

Answer 1

protons - atomic #
neutrons - 69-atomic #
electrons - atomic # + 2

= 34, 35, 36

Question 2

which of the following samples contains the greatest # of atoms?

all samples are 1.0g

Answer 2

1.0g -> moles of each substance -> atoms

whichever one has greatest is answer, likely substance with greatest molar mass, still check

Question 3

a 1.0g sample of which substance contains the largest # of molecules?

Answer 3

smallest molar mass = greatest # of molecules, vice versa

can also go from 1g -> mol -> molecules if needed and makes more sense to check

Question 4

the best name for Cr(SO4)3 is

Answer 4

chromium (VI) sulfate

Question 5

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?

Answer 5

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

Question 6

an oxide of manganese containing 2.29g of manganese per gram of oxygen. what is the empirical formula of this compound?

Answer 6

ignore the per, 2.29g + 1g

3.29g is total

solve as normal

percents -> g -> mole -> divide by lowest -> formula

Question 7

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

Answer 7

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

Question 8

under which conditions is the solubility of oxygen gas in water the greatest?

Answer 8

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

Question 9

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

Answer 9

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

Question 10

what is the oxidation # of Ti in the compound Na2Ti3O7?

Answer 10

4 - do right side first, left side second, calculate what is needed to match charge

Question 11

which reaction is spontaneous at all temperatures at standard pressure and concentration?

exo/endo RXN with increase/decrease in entropy?

Answer 11

exothermic reaction with an increase in entropy

just remember that spontaneous are exo

Question 12

what frequency of light has a wavelength of 455nm?

Answer 12

identify C, wavelength, finding frequency so…

use V=c/A

convert A to m

nm x 10^-9m

be careful of units

Question 13

how many orbitals have the quantum numbers … n = 4, l = 3, ml = 0

Answer 13

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

Question 14

which ionic compound has the smallest lattice energy?

AlN, NaF

Answer 14

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

Question 15

which property decreases from left to right across the periodic table and increases from top to bottom?

Answer 15

atomic radius

Question 16

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

Answer 16

pi bonds are stronger than sigma bonds

eliminate obvious and remember this

Question 17

what is the shape of the ClF3 molecule?

Answer 17

T-shaped

be careful, yes, draw out the molecule

3 bond 2 lone = t-shaped

Question 18

which of the following substances would exhibit dipole-dipole IMF?

Answer 18

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

Question 19

which arrangement has the correct order for decreasing boiling point?

Answer 19

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

Question 20

which of the following would likely have the lowest boiling point?

Answer 20

draw out all lewis dots

dipole dipole = high boiling

whichever molecule is non-polar = dispersion = lowest boiling

Question 21

which of the following substances has london dispersion forces as the only intermolecular force?

Answer 21

draw out all molecules

whichever molecule is non polar = only dispersion = answer

remember polarity from geometry or just looking at the structure

Question 22

the viscosity of liquids increase as…

Answer 22

think about syrup or honey

low temperature, high IMF

Question 23

which substance boils at the highest temperature?

Answer 23

another boiling point Q

draw out all structures, determine dipole-dipole, theres your answer

if two dipole-dipole, count electrons, most electrons wins

Question 24

what is the normal freezing point for the substance in the phase diagram?

Answer 24

evaluate phase diagram

normal = 1atm

go from 1 atm on the left side until you hit line, go down, theres your temp

Question 25

molecules will be nonpolar if…

Answer 25

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

Question 26

Planks constant is 6.626x10^-34Js, what is the value in kJms?

Answer 26

Jxs -> kJ (1/1000) -> ms (1/10^-6)

Question 27

what is the reading on the graduated cylinder to the right?

Answer 27

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

Question 28

what is the formula of iodic acid?

Answer 28

HIO3

Question 29

the density of helium is 0.164kg/m3. what is the density in lb/ft3?

Answer 29

kg -> lb then 1m/3.28^3

in general, just watch units

look at starting and where you are trying to get to

Question 30

what is the correct name for N2O5?

Answer 30

dinitrogen pentoxide

Question 31

what is the formula for hydroiodic acid?

Answer 31

HI

Question 32

using the models of particles below, which are isotopes of the same element?

Answer 32

evaluate all diagrams

isotopes = differing neutrons

SAME element = same electrons and protons

select answer this way

Question 33

chlorine occurs naturally as a mixture of two isotopes with atomic masses of 34.97 and 36.97. what are the relative abundances?

Answer 33

%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

Question 34

the element thallium, Tl, has two stable isotopes, 203Tl and 205Tl. which statement correctly describes the relationship between the relative abundances?

Answer 34

find molar mass of Tl, whichever isotope it is closest to will have greater abundance

hence, % abundance of 203Tl < % abundance of 205Tl

Question 35

if the formula of an ionic oxide of an element X is X2O3, what is the formula of the chloride of X?

Answer 35

Knowing that X has a +3 charge, when combining it with Cl which has a -1 charge, it is XCl3

Question 36

in all neutral atoms there are equal numbers of?

Answer 36

protons and electrons

Question 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?

Answer 37

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

Question 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?

Answer 38

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

Question 39

which group contains nonmetals, metalloids, and metals?

Answer 39

group 15

Question 40

the halogens are found in group?

Answer 40

17

Question 41

alkaline earth metals form what charge?

Answer 41

+2 ions/charge

Question 42

what is the wavelength of light (in nm) produced by the electronic transition between levels 4 and 2 of a hydrogen atom?

Answer 42

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)

Question 43

what is the ground state electron configuration for Zr2+?

Answer 43

(Kr)4d2

Question 44

what is the energy of a photon with a wavelength of 656nm?

Answer 44

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

Question 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?

Answer 45

use E=hv, plug and solve

Question 46

which electron transition in a hydrogen atom is associated with the largest emission energy?

Answer 46

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

Question 47

which emission line in the hydrogen spectrum occurs at the highest frequency?

Answer 47

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

Question 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?

Answer 48

eliminate obvious answers

for this specifically know that electrons no longer move in orbits in the current model

Question 49

what is the ground state electron configuration for the manganese atom? (Mn)

Answer 49

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

Question 50

what is the maximum number of electrons that can occupy an orbital labeled dxy?

Answer 50

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

Question 51

which of these species is/are paramagnetic?

Answer 51

write out electron config for each one

whichever one has unpaired and unfilled is paramagnetic

be careful with writing out configs

Question 52

the radii of the ions in this series decrease because

Answer 52

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

Question 53

which of these atoms will be the smallest?

Answer 53

follow trend of atomic radius if all atoms are neutral

if ions, follow trend of ionic radius using knowledge of Zeff, charge, etc

Question 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

Answer 54

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

Question 55

which ion is the smallest?

Na+
Al3+

Answer 55

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

Question 56

which ion has the largest radius?

K+
Cl-

Answer 56

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

Question 57

which pair of elements is listed in order of decreasing first ionization energy?

Na, Mg
Mg, Al

Answer 57

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

Question 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-<Ne<Na+

Answer 58

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

Question 59

what is the wavelength of a photon with an energy of 6.51x10^-9?

Answer 59

use E=hc/A

rearrange for A=hc/E

convert from m to nm by dividing by 10^-9

plug and solve

Question 60

an atom of Fe has two 4s electrons and 6 4d electrons. How many unpaired electrons would there be in an Fe2+ ion?

Answer 60

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 #

Question 61

what mass of carbon is present in 1.4x10^20 molecules of sucrose (C12H22O11)?

Answer 61

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

Question 62

a 4.08g sample of a compound of nitrogen and oxygen contains 3.02g of oxygen. what is the empirical formula?

Answer 62

g -> mol using molar masses -> divide by lowest mol amount -> turn into whole coefficients

Question 63

ibuprofen, a common pain reliever, contains 75.7g carbon, 15.5g oxygen, and 8.80g hydrogen by mass. what is the empirical formula?

Answer 63

g -> mol using molar masses -> divide by lowest mol amount -> turn into whole # coefficients

Question 64

which sample has the largest mass?

Answer 64

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

Question 65

a 10 gram sample of which substance contains the greatest number of hydrogen atoms?

Answer 65

g -> mole of compound -> mol of H -> molecules

do this for all compounds to find the greatest one

Question 66

a 25.0g of carbon dioxide contains X oxygen atoms

Answer 66

g -> mol Co2 -> mol of C using mole ratio -> atoms using avid#

Question 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?

Answer 67

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

Question 68

a 3.41x10^-6 g sample is known to contain 4.67x10^16 molecules. what is the compound?

Answer 68

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

Question 69

how many sodium ions are in 25.0g of Na2Co3

Answer 69

g -> mol -> mol of Na using mol ratio -> ions of Na using avid#

ions, molecules, atoms, all the same using avogadros #

Question 70

a sample of ethanol (C2H6O) contains 3.024g of hydrogen. how many moles of carbon are in the sample?

Answer 70

g -> mol hydrogen -> mols of C using mole ratio of ethanol

Question 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?

Answer 71

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

Question 72

what is the empirical formula of a compound of carbon, hydrogen, and oxygen that contains 51.56% carbon and 14.09%

Answer 72

first, change the %s to grams

g of element -> mol -> divide by lowest # -> turn into whole # coefficients

Question 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?

Answer 73

again, change the percentages to grams

g of element -> mols -> divide by lowest amount -> turn into whole # coefficients

Question 74

what is the empirical formula for a compound that is comprised of 54.0% Na, 8.50% B, 37.5% O?

Answer 74

again, same process

change percentages to g

g of each element -> respective mols -> divide by lowest amount -> turn into whole # coefficients

Question 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?

Answer 75

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

Question 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

Answer 76

solve for LR, mol of each reaction to mols of product

the least mol product = limiting reaction = theoretical yield

Question 77

what is the mass of TiO2 found when 0.476g TiCl4 are reacted with 0.501g H2O?

Answer 77

find LR then go from given g of LR -> mol of TiO2 -> g of TiO2

Question 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?

Answer 78

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

Question 79

a 2.32g sample of Na2So4 x nH2O yields 1.42g Na2SO4 upon reacting. What is the value of n?

Answer 79

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

Question 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?

Answer 80

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

Question 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?

Answer 81

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

Question 82

what amount of excess reagent remains when 0.30 mol NH3 reacts with 0.40 mol O2 to produce NO and H2O?

Answer 82

determine LR and ER

mol of LR -> mol of ER -> substract this solved mol of ER from the given amount of ER

Question 83

what amount of excess reagent remains when 0.500 mol Li reacts with 0.350 mol N2?

Answer 83

find LR and ER

given mol of LR -> mol of ER

subtract from given = remains

Question 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?

Answer 84

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

Question 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?

Answer 85

determine LR and ER normal way

g -> mol -> mol of product

the lesser amount = LR

mol of LR produced -> g of product = theoretical yield

Question 86

what amount of excess reagent remains when 4.0g zinc reacts with 2.0g of phosphorus?

Answer 86

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

Question 87

an initial reaction mixture of O2 and F2 is shown. which representation shows what would be present after the reaction is complete?

Answer 87

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

Question 88

which compound is a weak electrolyte when dissolved in water?

Answer 88

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

Question 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?

Answer 89

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

Question 90

what is the net ionic equation for the reaction between Na2S and Pb(NO3)2?

Answer 90

remember difference between net and total

net is the fully reduced, all spectator ions eliminated reaction

remember solubility rules as well

S2- + Pb2+ -> PbS

Question 91

for this reaction, what are the oxidizing and reducing agents?

2AuCl3 + 3H2 -> 2Au + 6HCl

Answer 91

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

Question 92

what is the molar concentration of a solution made by dissolving 8.58g of sodium acetate in water and diluting to 750.0mL?

Answer 92

g of sodium acetate -> mol of sodium acetate

M=mol/L

solve for molarity as normal

Question 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

Answer 93

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

Question 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?

Answer 94

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

Question 95

what is the molar concentration when 7.00mL of a 3.25M aq solution is distilled to 25.00mL

Answer 95

dilution problem given no reaction

first convert mL to L

use M1V1=M2V2

rearrange to solve for M2

Question 96

what volume in mL of 0.0557 M Sr(OH)2 is needed to neutralize 36.4mL of a 0.0750M HNO3 solution?

Answer 96

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

Question 97

when 1.0M aq solution of KI, NaC2H3O2, and Pb(NO3)2 are mixed together, what precipitate forms?

Answer 97

evaluate all options knowing solubility rules

eliminate obvious

whatever option is insoluble, no need to write out balanced EQ

Question 98

what is/are the spectator ions in this reaction?

HC3H2O2 + NaOH -> NaC2H3O2 + H2O

Answer 98

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

Question 99

which molecular equation would give this net ionic equation?

H+ + OH- -> H2O?

Answer 99

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

Question 100

what is a weak acid in water?

HBr
HF

Answer 100

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

Question 101

what particles would be present in NH3?

Answer 101

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

Question 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

Answer 102

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

Question 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?

Answer 103

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

Question 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

Answer 104

knowing the formula q=mcAT

we can solve for m by rearranging and knowing all other values

m=q/CAT

watch units, check yourself

Question 105

what is the enthalpy of formation for HF?

2HF-> H2+F2

Answer 105

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)

Question 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?

Answer 106

remember E=w+q

set E = 250

set q = 375

solve for w

hence, = -125

Question 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

Answer 107

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

Question 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

Answer 108

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

Question 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?

Answer 109

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

Question 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

Answer 110

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

Question 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?

Answer 111

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

Question 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

Answer 112

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

Question 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

Answer 113

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

Question 114

what is the order of ScN, MgO, CuCl2, and NaBr in order of increasing lattice energy?

Answer 114

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<CuCl2<MgO<ScN

Question 115

what is the formal charge of the nitrogen atom in nitric acid, HNO3?

Answer 115

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

Question 116

using the bond energies, what is the Hrxn for the reaction below?

Answer 116

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

Question 117

which molecule is nonpolar but contains polar bonds?

Answer 117

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

Question 118

The molecular orbital He22+ and He2 are shown here. what are the bond orders of He22+ and He2?

Answer 118

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

Question 119

arrange CsBr, NaCl, and RbBr in increasing magnitude of lattice energy

Answer 119

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<RbBr<NaCl

Question 120

how many covalent bonds are represented in the formula NH4Cl?

Answer 120

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

Question 121

the resonance structure for benzene indicates that

Answer 121

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

Question 122

what is the bond order of the C-O bond in the acetate ion?

Answer 122

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

Question 123

the lewis dot structure of ethanol is given below. estimate the enthalpy of combustion of ethanol using the bond enthalpies in the table

Answer 123

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

Question 124

for the nitrate ion, NO3-, predict the bond energy between nitrogen and the oxygen labeled A

Answer 124

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

Question 125

what is the molecular geometry around the N in the molecule depicted?

Answer 125

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

Question 126

according to vsepr, what are the approximate values of the bond angles X and Y?

Answer 126

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

Question 127

SCl2 has _ bonds and the overall molecule is _

polar or nonpolar?

Answer 127

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

Question 128

what are the polarities of the indicated molecules?

Answer 128

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

Question 129

which best illustrates a pi bond?

Answer 129

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

Question 130

what is the hybridization of the indicated molecule?

Answer 130

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

Question 131

how many sigma and pi bonds are in the molecule below?

Answer 131

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

Question 132

according to MO theory, f2 would?

mo diagram shown

Answer 132

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

Question 133

using the mo diagram given to the right, what is the bond order for N2-?

Answer 133

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)

Question 134

a gas behaves most ideally at

Answer 134

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

Question 135

what is the density of Xe gas at 70C and 2.50atm?

Answer 135

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

Question 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?

Answer 136

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

Question 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

Answer 137

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

Question 138

if the diagram shown is representative of particles in a sample of ideal gases, which statement is true?

Answer 138

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

Question 139

the graph to the right represents four different gasses at the same temperature, which are the correct labels for the curves?

Answer 139

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

Question 140

what is the correct order of increasing boiling point in NaCl, Br2, and ICl

Answer 140

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

Question 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?

Answer 141

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

Question 142

which sample deviates most from ideal gas behavior?

Answer 142

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

Question 143

what happens to the volume of a fixed amount of gas if both the pressure and absolute temp are doubled?

Answer 143

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

Question 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

Answer 144

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

Question 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

Answer 145

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

Question 146

suppose a gas contains equal moles of He and O2. Which is true?

Answer 146

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

Question 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?

Answer 147

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

Question 148

under the same conditions of temperature and pressure, H2 diffuses __ than O2

Answer 148

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

Question 149

why is the boiling point of Br2 higher than Cl2?

Answer 149

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

Question 150

which substance has the lowest vapor pressure at 25C?

Answer 150

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