Some more Some more Regents Chemistry Regents Chemistry

practice…practice…

What is the empirical formula What is the empirical formula of Cof C33HH66??

A: CH

D: CH6B: CH2

C: CH3

Empirical formula is the Empirical formula is the simplified version of a molecular simplified version of a molecular

formula…formula…

CC33HH66 – divide by greatest – divide by greatest

common factor (3) to get CHcommon factor (3) to get CH22

B

The name of the compound The name of the compound KClOKClO22, is potassium, is potassium

A: chlorine oxide

D: perchlorateB: chlorite

C: chlorate

ClOClO22– – is a polyatomic ion since is a polyatomic ion since

there is more than one capital there is more than one capital letter…letter…

go to Table E and keep it as isgo to Table E and keep it as is

B

What is the percent by mass What is the percent by mass of carbon in HCof carbon in HC22HH33OO22

(gram-formula mass is 60)?(gram-formula mass is 60)?

A: 12 / 60 * 100

D: 60 / 12 * 100B: 60 / 24 * 100

C: 24 / 60 * 100

Table T:Table T:% comp by mass = % comp by mass =

part / whole * 100 part / whole * 100

Since there are TWO carbon Since there are TWO carbon atoms…it is 24 / 60 * 100atoms…it is 24 / 60 * 100

C

What is the total volume What is the total volume occupied by 6.5 moles of COoccupied by 6.5 moles of CO2 (g)2 (g)??

A: 146 L

D: 6.5 LB: 3.4 L

C: 22.4 L

For ANY gas…1 mole occupies For ANY gas…1 mole occupies 22.4 L…22.4 L…

6.5 mol * 22.4 (L/mol) = 146 L6.5 mol * 22.4 (L/mol) = 146 L

A

The measure of the attraction for The measure of the attraction for electrons in a chemical bond iselectrons in a chemical bond is

A: ionization energy

D: electronegativity

B: atomic radius

C: attractivity

Electronegativity…Electronegativity…

you can look up those values in you can look up those values in Table S.Table S.

Ionization energyIonization energy is energy is energy required to remove an electron.required to remove an electron.

D

Given the equation:Given the equation:HH22 + Cl + Cl22 → 2 HCl→ 2 HCl

How many moles of HCl will be How many moles of HCl will be produced when 3 moles of Hproduced when 3 moles of H22 is is

completely consumed?completely consumed?

A: 3 moles

D: 0.7 molesB: 2 moles

C: 6 moles

HH22 + Cl + Cl22 → 2 HCl → 2 HCl

Set up a ratio:Set up a ratio:

eqn: 1 2eqn: 1 2 = =?:?: 3 x 3 x

C

What type of bond exists What type of bond exists between an atom of carbon and between an atom of carbon and

an atom of fluorine?an atom of fluorine?

A: ionic

D: nonpolar cov.B: metallic

C: polar cov.

Has to be Has to be covalentcovalent because two because two nonmetals…nonmetals…

Look up electronegativity values in Look up electronegativity values in Table S to see to that the difference Table S to see to that the difference

is greater than 1.is greater than 1.

Polar: ePolar: e-- shared UNequally shared UNequallyNonpolar: eNonpolar: e-- shared equally shared equally

C

Which is held together by Which is held together by metallic bonds?metallic bonds?

A: NaCl

D: Br2B: Fe

C: CO

Metallic bonding – Metallic bonding –

look for the metal…look for the metal…

FeFe

B

The primary forces of attraction The primary forces of attraction between water molecules between water molecules

in Hin H22O are O are

A: ionic

D: van der WaalsB: hydrogen

C: molecule-ion

Water molecules held together Water molecules held together by hydrogen bonding…by hydrogen bonding…

remember surface tension?remember surface tension?

floating a razor blade?floating a razor blade?

B

Which substance contains Which substance contains nonpolar covalent bonds? nonpolar covalent bonds?

A: H2

D: CaOB: H2O

C: Ca(OH)2

CovalentCovalent – – must be two NONMETALSmust be two NONMETALS

NonpolarNonpolar – – electrons shared equally…electrons shared equally…

electronegativity difference less electronegativity difference less than 1.than 1.

A

What describes the electron dot What describes the electron dot structure of CaClstructure of CaCl22??

A: brackets without charges

D: no brackets, but charges

B: no brackets, no charges

C: brackets with charges

CaClCaCl22 is is ionicionic (metal and nonmetal) (metal and nonmetal)

so needs brackets AND charges…so needs brackets AND charges…

C

CaCl Cl[ [[] ]]+2-1 -1

(lost 2 e-)(gained 1 e-) (gained 1 e-)

Which statement best describes Which statement best describes the following reaction?the following reaction?

Cl + Cl Cl + Cl → Cl→ Cl22 + energy + energy

A: bond formed & energy released

D: bond broken & energy absorbed

B: bond broken & energy released

C: bond formed & energy absorbed

Two reactants become one Two reactants become one product…product…

bond is formedbond is formed

Energy is on the product side…Energy is on the product side…energy is releasedenergy is released

A

The modern model of the atom The modern model of the atom shows that electrons areshows that electrons are

A: orbiting nucleus in fixed paths

D: located in a solid sphere covering nucleus

B: combined with neutrons in the nucleus

C: found in regions called orbitals

Modern model of atom = Modern model of atom = wave-mechanical model wave-mechanical model

ORORelectron cloud model…electron cloud model…

orbital = probable locations of eorbital = probable locations of e--

C

What is atomic number of an What is atomic number of an element that has 6 protons and 8 element that has 6 protons and 8

neutrons? neutrons?

A: 6

D: 14B: 2

C: 8

Atomic number = Atomic number =

number of protonsnumber of protons

A

What is the total number of What is the total number of protons contained in the nucleus protons contained in the nucleus

of a carbon-14 atom? of a carbon-14 atom?

A: 6

D: 14B: 8

C: 12

The “14” in carbon-14 The “14” in carbon-14 represents the mass number represents the mass number

(protons + neutrons). (protons + neutrons).

If the atom is carbon…If the atom is carbon…look up its atomic number.look up its atomic number.

A

Which of these elements has an Which of these elements has an atom with the most stable outer atom with the most stable outer

electron configuration? electron configuration?

A: Ca

D: NeB: Cl

C: Na

Look for the noble gases in Look for the noble gases in group 18…group 18…

They have full valence shells. They have full valence shells. (2 e(2 e-- for He, 8 e for He, 8 e-- for the rest) for the rest)

D

What is the nuclear charge of an What is the nuclear charge of an iron atom? iron atom?

A: +30

D: +82B: +26

C: +56

Protons and neutrons are in Protons and neutrons are in nucleus. Protons are positive and nucleus. Protons are positive and neutrons are neutral...making the neutrons are neutral...making the charge on the nucleus charge on the nucleus positivepositive. .

Look up atomic number of iron = 26.Look up atomic number of iron = 26.

B

How many electrons are in the How many electrons are in the outermost principal energy level of outermost principal energy level of an atom of bromine in the ground an atom of bromine in the ground

state? state?

A: 35

D: 8B: 7

C: 2

Look up the number of valence eLook up the number of valence e--……Electron config: 2-8-18-7Electron config: 2-8-18-7

Valence eValence e-- are last number = 7… are last number = 7…

Group 17 has 7 valence eGroup 17 has 7 valence e--. .

B

Which electron configuration is Which electron configuration is correct for a sodium ion? correct for a sodium ion?

A: 2-7

D: 2-8-2B: 2-8-1

C: 2-8

Na electron config as an Na electron config as an ATOMATOM is is

2-8-12-8-1

It is in group 1 and will lose its 1 It is in group 1 and will lose its 1 valence evalence e-- to become stable. to become stable.

C

The nucleus of which atom The nucleus of which atom contains 48 neutrons? contains 48 neutrons?

32

A: S 16

112

D: Cd 48

48

B: Ti 22

85

C: Rb 37

Mass number is top number = Mass number is top number = protons + neutronsprotons + neutrons

Atomic number is bottom number = Atomic number is bottom number = number of protonsnumber of protons

(protons + neutrons) – (protons) = (protons + neutrons) – (protons) = NEUTRONSNEUTRONS

C

When an atom loses an electron, When an atom loses an electron, the atom becomes an ion that is the atom becomes an ion that is

A: (+) and larger

D: (-) and smallerB: (-) and larger

C: (+) and smaller

Losing e-… (+) charge Losing e-… (+) charge (look at oxidation state)(look at oxidation state)

When you lose weight, for example, When you lose weight, for example, you become smaller…you become smaller…

the same goes for atoms & ions.the same goes for atoms & ions.

C

Spectral lines of elements are Spectral lines of elements are caused when electrons in an excited caused when electrons in an excited

state move fromstate move from

A: low to high energy levels, absorbing energy

D: high to low energy levels, releasing energy

B: high to low energy levels, absorbing energy

C: low to high energy levels, releasing energy

An atom absorbs energy…electron An atom absorbs energy…electron jumps to higher energy level.jumps to higher energy level.

(excited state)(excited state)

When the electron falls back to a lower When the electron falls back to a lower energy level, energy is released in the energy level, energy is released in the

form of light.form of light.(back to ground state)(back to ground state)

D

What happens when NaCl is What happens when NaCl is dissolved in water? dissolved in water?

A: Na+ ions attracted to O atoms of water

D: Cl- ions are repelled by the H atoms of water

B: Na+ ions are repelled by the O atoms of water

C: Cl- ions attracted to O atoms of water

Oxygen atoms have a partial Oxygen atoms have a partial negative charge so the Nanegative charge so the Na++ ions are ions are

attracted to that side of the water attracted to that side of the water molecule.molecule.

A

According to Table G, which solution According to Table G, which solution at equilibrium contains 50 g of solute at equilibrium contains 50 g of solute

per 100 g of water at 75˚C? per 100 g of water at 75˚C?

A: unsaturated solution of KCl

D: saturated solution of KClO3

B: saturated solution of KCl

C: unsaturated solution of KClO3

Saturated solution is when falls Saturated solution is when falls right on the curve.right on the curve.

Go over to 75 degrees and up to Go over to 75 degrees and up to 50 g of solute.50 g of solute.

B

Which compound is least soluble Which compound is least soluble in 100 g of water at 40in 100 g of water at 40˚C˚C? ?

A: SO2

D: NH4ClB: NaCl

C: KClO3

When you go over to 40 degrees When you go over to 40 degrees and then up…and then up…

SOSO22 is the first solute you run into, is the first solute you run into,

which means it is the least soluble.which means it is the least soluble.

A

What is the total number of What is the total number of moles of solute in 2.0 L of 3.0 M moles of solute in 2.0 L of 3.0 M

NaOH? NaOH?

A: 6 moles

D: 1 moleB: 2 moles

C: 3 moles

When you see “M” head to Table T:When you see “M” head to Table T:

molarity = (moles) / (liters)molarity = (moles) / (liters) x x

3 = 3 = 2 2

A

Real gases are like ideal gases atReal gases are like ideal gases at

A: high pressure & low temp

D: low pressure & high temp

B: low pressure & low temp

C: high pressure & high temp

At high temps, particles move fast At high temps, particles move fast and have less chance of attracting and have less chance of attracting

each other…each other…

At low pressure, particles won’t be At low pressure, particles won’t be so “squished” together and will be so “squished” together and will be

less likely to attract each other.less likely to attract each other.

D

As the temperature of a given As the temperature of a given sample of gas decreases at constant sample of gas decreases at constant

pressure, the volume of the gas pressure, the volume of the gas

A: decreases

D: smellsB: remains the same

C: increases

Temperature and volume have a Temperature and volume have a direct relationship…direct relationship…

they both increasethey both increaseoror

they both decrease.they both decrease.

A

2.0 L of CH2.0 L of CH44 and 2.0 L of O and 2.0 L of O22 have have

the same the same

A: density

D: # of atomsB: # of molecules

C: mass

They have the same volume so…They have the same volume so…

they have the same # of molecules they have the same # of molecules since they have the same # of since they have the same # of

moles.moles.

(6.02 x 10(6.02 x 102323 molecules in a mole) molecules in a mole)

B

Which phase is endothermic? Which phase is endothermic?

A: gas → solid

D: liquid → gas

B: gas → liquid

C: liquid → solid

Endothermic…Endothermic…

absorb energy.absorb energy.

A liquid must absorb energy to A liquid must absorb energy to become a gas.become a gas.

D

What happens to average kinetic What happens to average kinetic energy if temperature is energy if temperature is

increased? increased?

A: increases

B: decreases

C: remains the same

Think of average kinetic energy and Think of average kinetic energy and temperature as the same thing…temperature as the same thing…

A

What happens to temperature as What happens to temperature as water freezes? water freezes?

A: decreases

B: increases

C: remains the same

Temperature (average kinetic Temperature (average kinetic energy) remains the same during a energy) remains the same during a

phase change…phase change…

only potential energy changes only potential energy changes during a phase change.during a phase change.

C

Elements in a given period Elements in a given period contain the same number of contain the same number of

A: protons

D: # of energy levels

B: neutrons

C: valence e-

Going across period 4…Going across period 4…every element has 4 energy every element has 4 energy

levels.levels.

Examples: 2-8-8-1 & 2-8-18-6Examples: 2-8-8-1 & 2-8-18-6

D

Atoms of metals tend to Atoms of metals tend to

A: lose e- and form (-) ions

D: gain e- and form (+) ions

B: lose e- and form (+) ions

C: gain e- and form (-) ions

Metals only have a few valence Metals only have a few valence ee-- and want to lose e and want to lose e--..

Look at the oxidation for Look at the oxidation for metals…metals…

they are positive.they are positive.

B

Which two elements have Which two elements have chemical properties that are most chemical properties that are most

similar? similar?

A: Cl and Ar

D: C and NB: Li and Na

C: K and Ca

Elements in the same group Elements in the same group have the same # of valence ehave the same # of valence e--..

Elements with the same # of Elements with the same # of valence evalence e-- have similar chemical have similar chemical

properties.properties.

B

If M represents an alkali metal, what If M represents an alkali metal, what is the formula for the compound is the formula for the compound

formed by M and oxygen? formed by M and oxygen?

A: MO2

D: M3O2B: M2O

C: M2O3

Alkali metals = Group 1…Alkali metals = Group 1…

Group 1 form Group 1 form ++1 ions1 ions

MM+1+1OO-2-2…criss-cross……criss-cross…

MM22OO

B

As elements of Group 15 are As elements of Group 15 are considered from top to bottom, the considered from top to bottom, the metallic character of the atoms metallic character of the atoms

A: increases

B: decreases

C: remains the same

Metallic character increases Metallic character increases as you go down a group.as you go down a group.

A

Which Group 15 element exists Which Group 15 element exists as a diatomic molecule at STP? as a diatomic molecule at STP?

A: phosphorus

D: arsenicB: bismuth

C: nitrogen

Remember “HOF BrINCl”?Remember “HOF BrINCl”?

Hydrogen, oxygen, fluorine, Hydrogen, oxygen, fluorine, bromine, iodine, nitrogen, bromine, iodine, nitrogen,

chlorinechlorine

C

Properties of nonmetal atoms Properties of nonmetal atoms include include

A: low ionization energy and low electronegativity

D: high ionization energy and high electronegativity

B: low ionization energy and high electronegativity

C: high ionization energy and low electronegativity

Ionization energy = energy required to remove eIonization energy = energy required to remove e --..

High ionization energyHigh ionization energy because nonmetals want to because nonmetals want to GAIN, not lose eGAIN, not lose e--. .

Electronegativity = attraction for eElectronegativity = attraction for e -- when in a bond. when in a bond.

High electronegativityHigh electronegativity because nonmetals “pull because nonmetals “pull harder” on eharder” on e--..

JUST USE TABLE S!!!JUST USE TABLE S!!!

D

A redox reaction always A redox reaction always demonstrates the conservation of demonstrates the conservation of

A: mass

D: both mass and charge

B: neither mass or charge

C: charge

Both mass and charge will Both mass and charge will be conserved.be conserved.

D

What occurs when an atom is What occurs when an atom is oxidized? oxidized?

A: loss of e- and an increase in oxidation number

D: gain of e- and a decrease in oxidation number

B: loss of e- and a decrease in oxidation number

C: gain of e- and an increase in oxidation number

GGGRRRRR….GGGRRRRR….

Gain = reductionGain = reduction(charge reduced)(charge reduced)

Lose = oxidationLose = oxidation(charge icnreases – think of when (charge icnreases – think of when

metals lose emetals lose e--))

A

An electrochemical setup consists of two An electrochemical setup consists of two half-cells, an anode, a cathode, an half-cells, an anode, a cathode, an

external circuit, and a salt bridge. When a external circuit, and a salt bridge. When a rxn occurs, ion migration takes place rxn occurs, ion migration takes place

through the?through the?

A: anode

D: external circuit

B: cathode

C: salt bridge

Ions pass through salt bridge…Ions pass through salt bridge…

Electrons pass through external Electrons pass through external circuit.circuit.

C

The decomposition of water is forced The decomposition of water is forced to occur by use of an externally to occur by use of an externally applied electric current. This applied electric current. This

procedure is called procedure is called

A: neutralization

D: hydrolysisB: electrolysis

C: esterification

If an outside power source is If an outside power source is needed to get a chemical reaction to needed to get a chemical reaction to occur, it must be an electrolytic cell. occur, it must be an electrolytic cell.

Decomposing water is called… Decomposing water is called… electrolysis.electrolysis.

B

Which description is correct for a Which description is correct for a voltaic cell? voltaic cell?

A: spontaneous & anode is (-)

D: nonspontaneous & anode is (+)

B: nonspontaneous & anode is (-)

C: spontaneous & anode is (+)

Voltaic cells do NOT need an Voltaic cells do NOT need an outside power source, which outside power source, which

means they are means they are spontaneousspontaneous..

VAN…voltaic anode VAN…voltaic anode isis negative. negative.(opposite for electrolytic)(opposite for electrolytic)

A

Given the reaction: Given the reaction: Zn + HCl Zn + HCl → ZnCl→ ZnCl22 + H + H22

The oxidation number of H The oxidation number of H+1+1

decreases because itdecreases because it

A: loses protons

D: gains electronsB: gains protons

C: loses electrons

If charge decreases, HIf charge decreases, H+1+1 must must have been reduced.have been reduced.

Remember gaining Remember gaining negativenegative electrons makes it more electrons makes it more

negative.negative.

D

Which reaction occurs when Which reaction occurs when equivalent quantities of Hequivalent quantities of H++ and and

OHOH-- are mixed? are mixed?

A: oxidation

D: hydrolysisB: reduction

C: neutralization

Equal amounts of hydrogen ions Equal amounts of hydrogen ions and hydroxide ions makes a and hydroxide ions makes a

solution neutral…pH = 7.solution neutral…pH = 7.

C

What is the pH of a 0.01 M What is the pH of a 0.01 M solution of KOH?solution of KOH?

A: 1

D: 13B: 2

C: 12

Two steps:Two steps:

1. KOH is a base…[OH1. KOH is a base…[OH--] = 0.01] = 0.01 so pOH is 2. so pOH is 2.

2. 14 – pOH = pH 2. 14 – pOH = pH 14 – 2 = 12 14 – 2 = 12

C

The [HThe [H33OO++] of a solution is ] of a solution is

1 x 101 x 10-8-8. This solution has a pH of. This solution has a pH of

A: 6, which is acidic

D: 8, which is acidic

B: 8, which is basic

C: 6, which is basic

[H[H33OO++] is the hydronium ion…] is the hydronium ion…

think of it like the Hthink of it like the H++ ion. ion.

Just take the exponent and that will Just take the exponent and that will be the pH…8.be the pH…8.

0 – 7 is acidic 0 – 7 is acidic 7 – 14 is basic7 – 14 is basic

B

How many mL of 0.20 M KOH are How many mL of 0.20 M KOH are needed to completely neutralize needed to completely neutralize

90.0 mL of 0.10 M HCl?90.0 mL of 0.10 M HCl?

A: 25 mL

D: 180 mLB: 45 mL

C: 90 mL

Table T…titration equation.Table T…titration equation.

MMAAVVAA = M = MBBVVBB

(0.1) * (90) = (0.2) * X (0.1) * (90) = (0.2) * X

B

If a given solution contains [HIf a given solution contains [H++] = ] = 1 x 101 x 10-9-9, what is the [OH, what is the [OH--]?]?

A: 1 x 10-5

D: 1 x 10-1B: 1 x 10-9

C: 1 x 10-14

The exponents need to add The exponents need to add up to 14… up to 14…

1 x 101 x 10-5-5

A

Which compound is a strong Which compound is a strong Arrhenius base?Arrhenius base?

A: C2H5OH

D: NaOHB: CH3OH

C: HOH

Go toGo to Table L for bases and Table K Table L for bases and Table K for acids…for acids…

they are usually in those tables.they are usually in those tables.

HOH is water, both CHHOH is water, both CH33OH and OH and

CC22HH55OH are alcohols.OH are alcohols.

D

Methyl orange is used to test a Methyl orange is used to test a solution. If it turns red, what could solution. If it turns red, what could

the pH value be?the pH value be?

A: 3.0

D: 8.6B: 4.0

C: 4.4

Go to Table M for indicator Go to Table M for indicator questions.questions.

3.2 - 4.43.2 - 4.4

red - orange - yellowred - orange - yellow

A

Which statement best describes the Which statement best describes the solution produced when an Arrhenius solution produced when an Arrhenius

acid is dissolved in water?acid is dissolved in water?

A: only (-) ion in solution is OH-

D: only (-) ion in solution is HCO3

-B: only (+) ion in solution is H+

C: only (+) ion in solution is NH4

+

Acids produce [HAcids produce [H++] ions….] ions….

Bases produce [OHBases produce [OH--] ions.] ions.

B

Which formula represents a Which formula represents a saturated compound?saturated compound?

A: C2H4

D: C3H8B: C3H6

C: C2H2

Only alkanes are saturated…Only alkanes are saturated…

saturatedsaturated hydrocarbons have the hydrocarbons have the most hydrogens possible…most hydrogens possible…

the compound needs all single the compound needs all single bonds.bonds.

D

What describes two isomers of a What describes two isomers of a hydrocarbon?hydrocarbon?

A: same formula, same structure

D: different formula, same structure

B: different formula, different structure

C: same formula, different structure

Isomers have the same formula, but Isomers have the same formula, but the atoms are arranged differently.the atoms are arranged differently.

Two isomers of pentane will both Two isomers of pentane will both have 5 carbons and 12 hydrogens…have 5 carbons and 12 hydrogens…they will just be arranged differently.they will just be arranged differently.

C

What is the maximum number of What is the maximum number of covalent bonds that can be formed covalent bonds that can be formed

by one carbon atom?by one carbon atom?

A: 1

D: 4B: 2

C: 3

Carbon has 4 valence electrons and Carbon has 4 valence electrons and will need to form 4 bonds to will need to form 4 bonds to complete its valence shell.complete its valence shell.

D

A compound with the formula A compound with the formula CHCH33CHCH22OH is classified as anOH is classified as an

A: alkane

D: acidB: alcohol

C: alkene

Table R…Table R…

the –OH functional group makes it the –OH functional group makes it an alcohol.an alcohol.

B

How many bromine atoms are in How many bromine atoms are in the compound the compound

1,1-dibromopropane?1,1-dibromopropane?

A: 1

D: 4B: 2

C: 3

Di- means 2.Di- means 2.

The “1,1” tells you location of each The “1,1” tells you location of each of the bromine atoms. So you can of the bromine atoms. So you can

count the numbers also. count the numbers also.

B

Which formula represents Which formula represents ethanoic acid?ethanoic acid?

A: CH3CHO

D: CH3CH2CHOB: CH3CH2COOH

C: CH3COOH

Eth- means two carbons.Eth- means two carbons.

Table R…Table R…-COOH functional group means -COOH functional group means

organic acid. organic acid.

C

What is the name of the chemical What is the name of the chemical reaction when glucose decomposes reaction when glucose decomposes

into carbon dioxide and ethanol?into carbon dioxide and ethanol?

A: fermentation

D: combustionB: addition

C: substitution

Fermentation…Fermentation…decomposition would also work. decomposition would also work.

A

When radium-226 undergoes When radium-226 undergoes natural transmutation, it emits natural transmutation, it emits

A: an alpha particle

B: a beta particle

C: a position

D: a neutron

Table N…Table N…

find radium-226 and look for find radium-226 and look for decay mode. decay mode.

A

Which type of radiation has zero Which type of radiation has zero mass and zero charge?mass and zero charge?

A: alpha

B: beta

C: gamma

D: neutron

Table O...Table O...

00 γγ

00

C

What type of radiation has the What type of radiation has the weakest penetrating power?weakest penetrating power?

A: alpha

B: beta

C: gamma

D: neutron

Alpha particles are big and slow Alpha particles are big and slow and won’t pass through paper.and won’t pass through paper.

A

What type of radiation has the What type of radiation has the weakest In how many days will a 12 g weakest In how many days will a 12 g sample of iodine-131 decay, leaving sample of iodine-131 decay, leaving

1.5 g of the original isotope?1.5 g of the original isotope?

A: 8

B: 16

C: 20

D: 24

Four half-lives…Four half-lives…

1: 12 – 61: 12 – 6

2: 6 – 32: 6 – 3

3: 3 – 1.5 3: 3 – 1.5

D