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IB Chem Unit 6 Test

Terms in this set (91)

Which is the correct order based on increasing strength?
A. covalent bonds < hydrogen bonds < dipole-dipole forces < dispersion forces
B. dipole-dipole forces < dispersion forces < hydrogen bonds < covalent bonds
C. dispersion forces < dipole-dipole forces < hydrogen bonds < covalent bonds
D. dispersion forces < dipole-dipole forces < covalent bonds < hydrogen bonds
dispersion forces < dipole-dipole forces < hydrogen bonds < covalent bonds
electrostatic force of attraction
an attractive and repulsive force between particles caused by their electric charges. The electric force between stationary charged bodies is conventionally known as the electrostatic force. It is also referred to as Columb's force.
Lewis Structure
models of molecules, containing the valence shell and electrons . It is used to show how the electrons are arranged around individual atoms in a molecule. Electrons are shown as "dots" or for bonding electrons as a line between the two atoms.
valence-shell electron pair repulsion model (VSEPR)
theory that explains the shapes of molecules. States that electron pairs will repel each other such that the shape of the molecule will adjust so that the valence electron-pairs stay as far apart from each other as possible.
bond
an electrostatic force of attraction that brings particles together
resonant bond / resonance
a mental exercise within the Valence Bond Theory of bonding that describes the delocalization of electrons within molecules. It involves constructing multiple Lewis structures that, when combined, represent the full electronic structure of the molecule.
bonding pair
consists of two electrons shared between atoms, creating a bond
lone pair (of an atom)
A lone pair of an atom consists of two electrons not involved in a bond
electron domain
refers to the number of lone pairs or bond locations around a particular atom in a molecule, may also be called electron groups.
formal charge (of an atom)
Tells you if an atom is negative, positive, or neutral? Here's the formula
FC = [# of valence electrons] - [electrons in lone pairs + 1/2 the number of bonding electrons]
Bond enthalpy
describes the amount of energy stored in a bond between atoms in a molecule. The strength of a bond depends on the force of attraction and is related to this.
Lattice enthalpy
is a measure of the strength of the forces between the ions in an ionic solid. The greater the enthalpy, the stronger the forces.
electronegativity
the measurement of how much an atom wants to bond to another atom. These differences lead to a SPECTRUM of polarities which affects the properties of the compound.
dipole moment
occur when there is a separation of charge. They can occur between two ions in an ionic bond or between atoms in a covalent bond; they arise from differences in electronegativity. ... it is a measure of the polarity of the molecule.
polarity
A lack of electrical symmetry in a molecule. Charge differences on opposite ends of a structure.( oppositely charged)...non-polar means equally charged.
van der Waals forces
a slight attraction that develops between the oppositely charged regions of nearby molecules
London Dispersion Forces (LDF)
a temporary attractive force that results when the electrons in two adjacent atoms occupy positions that make the atoms form temporary dipoles
dipole-dipole forces
attractive forces between the positive end of one polar molecule and the negative end of another polar molecule. ... They are much weaker than ionic or covalent bonds and have a significant effect only when the molecules involved are close together (touching or almost touching).
hydrogen bond
A type of weak chemical bond formed when the slightly positive hydrogen atom of a polar covalent bond in one molecule is attracted to the slightly negative atom of a polar covalent bond in another molecule.
polar covalent bond
bond in which electrons are not shared equally
Allotropes
different molecular structures of the same element
four allotropes of carbon
diamond, graphite, graphene and fullerene.
metallic bonding
positively charged metallic ions are surrounded by a cloud of valence electrons
complex ions
has a metal ion at its centre with a number of other molecules or ions surrounding it
Pi bond (π bond):
a chemical bond between atoms in a molecule having overlapping p orbitals
Sigma bond (σ bond):
A covalent bond formed by overlap of atomic orbitals
Hybridization
the mixing of several atomic orbitals to form the same total number of equivalent hybrid orbitals
A Shortcut For Determining The Hybridization Of An Atom In A Molecule
Count the number of atoms connected to it (atoms - not bonds!)
Count the number of lone pairs attached to it.
Add these two numbers together.
If it's 4, your atom is sp3.
If it's 3, your atom is sp2.
If it's 2, your atom is sp.
(If it's 1, it's probably hydrogen!)
mass spectroscopy
an analytical tool useful for measuring the mass-to-charge ratio (m/z) of one or more molecules present in a sample. These measurements can be used to calculate the exact molecular weight.
H-NMR Spectroscopy
proton NMR is a type of absorption spectroscopy which tells us
1- the # of sets of peaks in the spectrum tells 1 of the # of chemically nonequivalent sets of protons in the molecule
2- the splitting pattern of each set of peaks tells how many protons are interacting with the protons in that set
IR spectroscopy
(IR) Infra Red light causes bonds to vibrate at different frequencies, shows which functional groups are present

peaks expressed as wavenumbers (cm-1)
IHD (index of hydrogen deficiency)
provides information about the number of double or triple bonds in a molecule
The number of hydrogen molecules, H2, needed to convert the molecule to the corresponding saturated, non-cyclic molecule.**Drawing out the structure is a much faster way to solve IHD problems**draw the structure and identify rings and double and triple bonds, counting each one as an IHD value of 1.
X-ray crystallography
A technique used to study the three-dimensional structure of molecules. It depends on the diffraction of an X-ray beam by the individual atoms of a CRYSTALLIZED molecule.
By making reference to intermolecular forces, suggest the relative
volatilities of SCl2 and H2O.
H O forms hydrogen bonding and London/disperson forces AND SCl forms
dipole-dipole and London/disperson forces ✓

Alternative 1:
H O less volatile AND H O has hydrogen bonding which is stronger than
dipole-dipole and dispersion forces in SCl ✓

Accept "SCl has «much» larger molar mass/electron density" for M2.

Nickel catalyses the conversion of propanone to propan-2-ol.
Nickel catalyses the conversion of propanone to propan-2-ol.
*SEE SKETCH BOOK #1*

Discuss, referring to intermolecular forces present, the relative volatility of propanone and propan-2-ol.,
hydrogen bonding/bonds «and dipole-dipole and London/dispersion forces are
present in» propan-2-ol ✔
dipole-dipole «and London/dispersion are present in» propanone ✔
propan-2-ol less volatile AND hydrogen bonding/bonds stronger «than dipole-
dipole »
OR
propan-2-ol less volatile AND «sum of all» intermolecular forces stronger ✔
What is the order of increasing strength of intermolecular forces?
A. CH CH CH CH < CH CH(OH)CH < CH COCH < CH CO H
B. CH CH CH CH < CH COCH < CH CH(OH)CH < CH CO H
C. CH CO H < CH COCH < CH CH(OH)CH < CH CH CH CH
D. CH CH CH CH < CH COCH < CH CO H < CH CH(OH)CH
CH CH CH CH < CH COCH < CH CH(OH)CH
< CH CO H
Which compound has hydrogen bonds between its molecules?
A. CH
B. CH O
C. CH Cl
D. CH O
CH O
Ethyne, C H , reacts with oxygen in welding torches.
Identify the type of interaction(force) that must be overcome when liquid
ethyne vaporizes.
London/dispersion/instantaneous dipole-induced dipole forces

Product B, CH CHO, can also be synthesized from ethanol.
Product B is an aldehyde and has a C=O on the final carbon. Based on
the structure of product B, suggest why it is water soluble.
that can form hydrogen bonds/H-bonds «with water molecules»
or
«large permanent» dipole-dipole interactions with water
or
has an oxygen/O atom with a lone pair
What are the strongest intermolecular forces between molecules of
propanone, CH COCH , in the liquid phase?
A. London (dispersion) forces
B. Covalent bonding
C. Hydrogen bonding
D. Dipole-dipole forces
Dipole-dipole forces
The compounds shown below have similar relative molecular masses.
What is the correct order of increasing intermolecular force strength and
increasing boiling point?
A. CH COOH < (CH ) CO < (CH ) CHOH
B. CH COOH < (CH ) CHOH < (CH ) CO
C. (CH ) CO < CH COOH < (CH ) CHOH
D. (CH ) CO < (CH ) CHOH < CH COOH
(CH ) CO < (CH ) CHOH < CH COOH
Butanoic acid, CH CH CH COOH, is a weak acid and ethylamine, CH CH NH , is a weak base.
Explain why butanoic acid is a liquid at room temperature while
ethylamine is a gas at room temperature.
Any two of:
-butanoic acid forms more/stronger hydrogen bonds
-butanoic acid forms stronger London/dispersion forces -butanoic acid forms stronger dipole-dipole interaction/force

Accept "butanoic acid forms dimers"
Accept "butanoic acid has larger M /hydrocarbon chain/number of electrons" for M2.
Accept "butanoic acid has larger «permanent» dipole/more polar" for M3.
Urea, (H N) CO, is excreted by mammals and can be used as a fertilizer.
Suggest one reason why urea is a solid and ammonia a gas at room
temperature.
Any one of:
-urea has more hydrogen bonding
-urea is more polar/has greater dipole moment
-urea has greater molar mass
-urea has greater electron density/greater London/dispersion

Accept "urea has larger size/greater van der Waals forces".
Sketch two different hydrogen bonding interactions between ammonia
and water.
*See sketch book #2*
If lone pairs are shown on N or O, thenthe lone pair on N or one of the lone pairs on O MUST be involved in the H-bond.
~Penalize solid line to represent H-bonding only once.~
Which of the following series shows increasing hydrogen bonding with
water?
A. Propane < propanal < propanol < propanoic acid
B. Propane < propanol < propanal < propanoic acid
C. Propanal < propane < propanoic acid < propanol
D. Propanoic acid < propanol < propanal < propane
Propane < propanal < propanol < propanoic acid
Which correctly states the strongest intermolecular forces in the
compounds below?
A. CH4 dipole-dipole, CH3CL London Forces CH3NH2 Hydrogen Bonding.
B. CH4 London Forces , CH3CL dipole-dipole, CH3NH2 Hydrogen Bonding.
C. CH4 Hydrogen Bonding, CH3CL London Forces, CH3NH2 dipole-dipole
D. CH4 London Forces, CH3CL Hydrogen Bonding, CH3NH2 dipole-dipole
CH4 London Forces , CH3CL dipole-dipole, CH3NH2 Hydrogen Bonding.
Which bonds cause the boiling point of water to be significantly greater than that of hydrogen sulfide?
A. London (dispersion)
B. Covalent
C. Ionic
D. Hydrogen
Hydrogen
Bonds can be formed in many ways.
The landing module for the Apollo mission used rocket fuel made from a mixture of hydrazine, N H , and dinitrogen tetraoxide, N O .
N H (l) + N O (l) → 3N (g) + 4H O(g)
State why hydrazine has a higher boiling point than dinitrogen
tetraoxide.
hydrogen bonding «between molecules, dinitrogen tetraoxide does not»
HERE ́S A THROWBACK TO REDOX!!!
Deduce, giving a reason, which species is the reducing agent in this reaction.
N H (l) + N O (l) → 3N (g) + 4H O(g)
N H AND oxidized/oxidation state increases
OR
N H AND loses hydrogen
OR
N H AND reduces/removes oxygen from N O
Accept "N H AND gives electrons «to N O »".
Deduce the Lewis structure of ozone and state what type of
intermolecular forces exist in ozone.
*See sketch book #3*
Do not accept structure that represents 1.5 bonds.
only London/disperson forces!!!
Trends in physical and chemical properties are useful to chemists.
Explain why the melting point of the group 17 elements,
the Halogens, (F → I) increase down the group.
radius increases as you go down the group
number of electrons/surface area/molar mass increase
all are diatomic and are non-polar
have only London/dispersion forces
as radius of diatomic molecule increases, dipole moments are more polar, thus
London/dispersion force strength increases
Cobalt forms the transition metal complex [Co(NH ) (H O)Cl]Br.
State the shape of the complex ion.
octahedral
Oxygen exists as two allotropes, diatomic oxygen, O , and ozone, O .
Discuss the relative length of the two O−O bonds in ozone.
both equal ✔
delocalization/resonance ✔
Accept bond length between 121 and 148 pm/ that of single O−O bond and
double O=O bond for M1.
Explain why there are frequencies of UV light that will dissociate O3 but not O2.
bond in O is weaker
OR
O bond order 1.5/< 2
lower frequency/longer wavelength «UV light» has enough energy to break the
O-O bond in O «but not that in O » ✔
Accept "lower frequency/longer wavelength «UV light» has lower energy".
Explain, using equations, how the presence of results in a chain
reaction that decreases the concentration of ozone in the stratosphere.
CCl2F2(g) →∙CClF2(g) Cl ∙ (g)
Cl∙(g)+O3(g)→O2(g)+ClO∙(g)
AND
ClO∙(g)+O3(g)→2O2(g)+Cl ∙ (g)

Do not penalize missing radical.
Accept:for M2:
Cl∙(g) + O3(g) → O2(g) + ClO ∙ (g)
AND
ClO∙(g) + O(g) → O2(g) + Cl ∙ (g)
Chlorine undergoes many reactions.
2. 67 g of manganese(IV) oxide was added to 200. 0 cm of 2. 00 mol dm−3 HCl.
MnO2 (s) + 4 HCl (aq) → Cl2 (g) + 2H2O (l) + MnCl2 (aq)
Calculate the volume of chlorine in dm3,
produced if the reaction is conducted at standard temperature and pressure (STP). Use section 2 of the data booklet.
HINT....... you must determine the L________ R_________
«0. 0307 mol × 22. 7 dm3 mol
−1 = » 0. 697 «dm3 »
Accept methods employing pV=nRT.
Chlorine gas reacts with water to produce hypochlorous acid and hydrochloric acid.
Cl2 (g) + H2O (l) ⇌ HClO (aq) + HCl (aq).

Calculate the concentration of H+ (aq) in a HClO(aq) with a
pH = 3. 61.
«[H+] = 10−3.61 = »2. 5 × 10−4 «mol dm−3 »
CCl2 F2 is a common chlorofluorocarbon, .
Comment on how international cooperation has contributed to the
lowering of emissions responsible for ozone depletion.
research «collaboration» for alternative technologies «to replace CFCs»
OR
technologies «developed»/data could be shared
OR
political pressure/Montreal Protocol/governments passing legislations
Accept reference to agreement on banning use/manufacture of CFCs.
The equations show steps in the formation and decomposition of ozone in the stratosphere
Step 1 O → 2O•
Step 2 O• + O → O
Step 3 O → O• + O
Step 4 O• + O → 2O

State which steps absorb UV light.
O → 2O and O → O• + O
Outline why both bonds in the ozone molecule are the same length and predict the bond length in the ozone molecule. Refer to section 10 of the data booklet.
resonance «structures»
OR
delocalization of «the double/pi bond» electrons ✔
121 «pm» < length < 148 «pm» ✔
Will Accept any length between these two values.
Predict the bond angle in the ozone molecule.
any value from 110°-119°
Discuss how the different bond strengths between the oxygen atoms in O and O in the ozone layer affect radiation reaching the Earth's
surface.
«bond» in O stronger than in O
ozone absorbs lower frequency/energy «radiation than oxygen»
OR
ozone absorbs longer wavelength «radiation than oxygen»
Will Accept ozone «layer» absorbs a range of frequencies.
Determine, showing your working, the wavelength, in m, of ultraviolet
light absorbed by a single molecule in one of these steps. Use sections 1, 2 and 11 of the data booklet.
NOTE...( ) represnts to the power of... :)
ALTERNATIVE 1:
for oxygen:

E =«498000 Jmol (-1) /
6.02 × 10(23)mol (-1)=
» 8.27 × 10(−19) «J»


λ = « 6.63 × 10(−34) Js× 3.00 × 10(8)ms(−1) /
8.27 × 10(−19) J =
» 2.40 × 10(−7) «m»


ALTERNATIVE 2:
for ozone:
similar calculation using 200 < bond enthalpy < 400 for ozone, such as

E = « 300000 Jmol (−1) /
6.02 × 10(23) mol (-1) =
» 4.98 × 10(−19) «J»

λ = «6.63 × 10(−34) Js × 3.00 × 10(8)
ms−1 /
4.98 x 10(−19) J =
» 3.99 × 10(−7) «m»
Ozone depletion is catalysed by nitrogen monoxide, NO, which is
produced in aircraft and motor vehicle engines, and has the following
Lewis structure.
*See Sketch Book # 4**
Show how nitrogen monoxide catalyses the decomposition of ozone, including equations in your answer.
•NO + O → •NO + O ✔
•NO + O → •NO + 2O ✔
NOTE: Accept •NO → •NO + •O AND •O + O → 2O for M2.
Dinitrogen monoxide, N O, causes depletion of ozone in the stratosphere.
Outline why ozone in the stratosphere is important.
absorbs UV/ultraviolet light «of longer wavelength than absorbed by O2 »
Dinitrogen monoxide in the stratosphere is converted to nitrogen
monoxide, NO (g).
Write two equations to show how NO (g) catalyses the decomposition of ozone.
NO (g) + O (g) → NO (g) + O (g)
NO (g) + O (g) → NO (g) + 2O (g)

Note: Ignore radical signs.
Accept equilibrium arrows.
Award [1 max] for NO (g) + O (g) → NO (g) + O (g).
The Lewis (electron dot) structure of the dinitrogen monoxide molecule can be represented as:
**SEE Sketch Book #5**
State what the presence of alternative Lewis structures shows about the nature of the bonding in the molecule.
delocalization
OR
delocalized π-electrons

Note: Accept "resonance".
Some physical properties of molecular substances result from the different types of forces between their molecules.
Absorption of UV light in the ozone layer causes the dissociation of
oxygen and ozone.
Identify, in terms of bonding, the molecule that requires a longer wavelength to dissociate.
O has bond between single and double bond AND O has double bond
OR
O has bond order of 1.5 AND O has bond order of 2
OR
bond in O is weaker/longer than in O
O requires longer wavelength

DO NOT ACCEPT!!!! "ozone has one single and one double bond". NO NO!
What can be deduced from the facts that ozone absorbs UV radiation in the region of 340 nm and molecular oxygen in the region of 242 nm?
The bonds between atoms in molecular oxygen need more energy to break.
Which is the first step in the CFC-catalysed destruction of ozone in UV
light?
A. CCl F → CClF + Cl
B. CCl F → •CClF + Cl•
C. CCl F → CCl F + F
D. CCl F → •CCl F + F•
CCl F → •CClF + Cl•
There is concern about damage done to the ozone layer in the stratosphere by jet-propelled aircraft.
Formulate two equations to show how nitrogen(II) oxide, NO, catalyses the destruction of ozone.
NO ∙ (g) + O3(g) → NO2 ∙ (g) + O2(g)
NO2 ∙ (g) + O ∙ (g) → NO ∙ (g) + O2(g)
or
NO2 ∙ (g) + O3(g) → NO ∙ (g) + 2O2(g)
Suggest why the loss of ozone is an international environmental
concern.
«loss of ozone» allows UV radiation to penetrate atmosphere/reach earth
UV radiation causes skin cancer
OR
UV radiation causes tissue damage
Draw the Lewis (electron dot) structures of oxygen, , ozone, , and
hydrogen peroxide, .
**See Sketch Book #6***
The coordinate bond may be represented as an arrow and the formal charges
may be shown.
Do not accept delocalized structure.
See Sketch #6
Deduce, giving a reason, the relative lengths of the oxygen to oxygen bonds in oxygen and hydrogen peroxide.
O2 < H2O2 O2 has double bond/bond order of 2 (and H2O2 has single bond/bond order of 1)
Predict, with a reason, the O−O−O bond angle in O3
Any value in the range 110° to 120°;
Experimental value = 117°.
Accept 120°.
Do not accept 109°.
3 negative charge centres/electron domains with 1 lone pair / lone pair-bond
(pair) repulsion greater than bond (pair)-bond (pair) repulsion / lone pair
occupies more space than bond (pair)/shared pair (so O-O-O angle reduced);
Do not apply ECF in this question.
What is the best description of the carbon-oxygen bond lengths in CO3 2- ?
Three bonds of the same length
Which of the following contain a bond angle of 90°?
I. PC14 +
II. PCl5
III. PCl6 -
II and III only
Which allotropes contain carbon atoms with sp 2 hybridization?
I. Diamond
II. Graphite
III. C60 fullerene
II and III only
What is the molecular shape and the hybridization of the nitrogen atom in NH3?
trigonal pyramidal (sp 3)
True or False
Sigma bonds are formed by either s or p orbitals, pi bonds are formed only by p orbitals.
True
Which statements are correct?
I. All carbon-oxygen bond lengths are equal in CO3 2- .
II. All carbon-oxygen bond lengths are equal in CH3COOH.
III. All carbon-oxygen bond lengths are equal in CH3COO - .
I and III only
Which statement is correct about multiple bonding between carbon atoms?
A. Double bonds are formed by two π bonds.
B. Double bonds are weaker than single bonds.
C. π bonds are formed by overlap between s orbitals.
D. π bonds are weaker than sigma bonds.
π bonds are weaker than sigma bonds.
Which types of hybridization are shown by the carbon atoms in the compound CH2 = CH-CH3?
I. sp
II. sp 2
III. sp 3
II and III only
Identify the types of hybridization shown by the carbon atoms in the molecule CH3CH2CH2COOH
I. sp
II. sp 2
III. sp 3
II and III only
Which molecule is square planar in shape?
A. XeO4
B. XeF4
C. SF4
D. SiF4
XeF4
What is the molecular geometry and the Cl-I-Cl bond angle in the ICl4 - ion?
Square planar 90°
What is the geometry of the bonds around an atom with sp 2 hybridization?
3 bonds at 120°
.How many sigma (σ) and pi (π) bonds are present in the structure of HCN?
σ 2, π 2
How many lone pairs and bonding pairs of electrons surround xenon in the XeF4 molecule?
Lone pairs 2, Bonding pairs 4
Sigma and pi bonds are chemical covalent bonds.
How is a sigma bond formed?
They are formed by end-to-end overlapping atomic orbitals.
Sigma and pi bonds are chemical covalent bonds.
How is a pi bond formed?
They are formed when the lobe of one atomic orbital overlaps another.
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