Reviewing Liquids and Solids

Chem I | Chem II AP
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1)
Substance X has very strong intermolecular forces. Rate the following properties as high/low or strong/weak.
a)
Boiling point
b)
Melting point
c)
Surface tension
d)
Viscosity
e)
Evaporation rate
f)
Vapor pressure
2)
What is the relationship between:
a)
Vapor pressure vs. temperature
b)
Boiling point. vs. atmospheric pressure
c)
Vapor pressure vs. intermolecular forces
3)
Place the following substances in order of increasing boiling point. (Mark the lowest bp as #1 and the highest bp as #4)
H2O
Ne
H2S
KCl
H2O has hydrogen bonding, Ne has LDF, H2S has dipole-dipole attractions and KCl is ionic.
4)
Choose the correct answer:
a)
Higher boiling point
Both nitrogen and iodine are held together by LDF. Iodine has many more electrons than nitrogen so it is more polarizable and has stronger IMF. This means iodine has the higher boiling point.
b)
Lower vapor pressure
Carbon tetrachloride is symmetrical and so is held together by LDF. Water has LDF but also hydrogen bonding. Although CCl4 has significantly more electrons and therefore stronger LDF than water, that is not enough to overpower the hydrogen bonding in water. Both substances are liquids at room temperature but water has the higher boiling point and therefore the lower vapor pressure.
c)
Higher vapor pressure
N2 is held together by LDF only and water has both LDF and hydrogen bonding. The hydrogen bonding in water is stronger than the LDF in nitrogen as evidenced by the fact that nitrogen is a gas at room temperature and water is a liquid. Since nitrogen has weaker IMF, it will have a higher vapor pressure.
d)
Greater viscosity
He is held together by LDF only and water has both LDF and hydrogen bonding. The hydrogen bonding in water is stronger than the LDF in helium as evidenced by the fact that helium is a gas at room temperature and water is a liquid. Since water has stronger IMF, it will have a greater viscosity.
e)
Greater heat of vaporization
NaCl is ionic, HF is hydrogen bonding. Although hydrogen bonding is the strongest type of molecular IMF, it is not as strong as the electrostatic attractions between positive and negative ions.
f)
Higher melting point
There is LDF but also some hydrogen bonding in C3H7OH which gives it a higher melting point than C4H10 which is only LDF. Both molecules have approximately the same number of electrons so the strength of the LDF is not an issue.
g)
Higher vapor pressure
SiO2 is network covalent and therefore doesn't evaporate quickly (if at all). CO2 is held together by LDF which is a weak force and therefore it evaporates easily. Alternately, SiO2 is a solid so it has a lower vapor pressure than CO2 which is a gas.
5)
What attractive forces would have to be broken in order for the following substances to vaporize?
a)
CO2
b)
HCl
c)
HF
d)
C2H6
e)
Ca(NO3)2
f)
Cu
g)
C(dia)
6)
Given: C(dia), LiF, Mg, H2O, O2
Cdia is network covalent, LiF is ionic, Mg is metallic, H2O is molecular covalent with hydrogen bonding, O2 is molecular covalent with LDF.
a)
Highest melting point
b)
Greatest hardness
c)
Conducts as a solid
d)
Conducts if molten

Mg and LiF both conduct electricity when melted.

e)
LDF
f)
Metallic bonding
g)
Hydrogen bonding
h)
Highest vapor pressure
i)
Lowest boiling point
7)
Which type/s of solid
a)
Has the highest melting points
Network covalent has the highest melting points because to melt a network covalent substance, actual covalent bonds must be broken.
b)
Dissolves in water
Both ionic and (polar) molecular covalent dissolve in water.
c)
Conducts electricity when liquid or dissolved
Both ionic and metallic conduct electricity when liquid. Only ionic conducts electricity when dissolved because metals are not soluble.
d)
Conducts electricity when solid
Metallic conducts electricity when solid because the sea of electrons is able to move between the positive ions.
e)
Has the lowest melting points
Molecular covalent have the lowest melting points because they are held together by weak intermolecular forces not stronger electrostatic attractions or covalent bonds.
f)
Is composed of atoms
Network covalent is composed of atoms joined in a network of covalent bonds. Molecular covalent also includes atoms such as the noble gases (He, Ne, Ar, Kr, Rn). Although the noble gases are not molecules, they are held together by LDF just like nonpolar molecules so they are grouped with molecular covalent.
g)
Is composed of molecules
Only molecular covalent is composed of actual molecules held together by IMF rather than ions or atoms held together by stronger forces.
8)
For the following statements, agree or disagree and provide a justification for your answer:
a)
Water’s relatively high mp for a small molecule is due to its strong covalent bonds
b)
Solid potassium would be expected to be a better conductor than solid KCl.
c)
BeO would be expected to have a lower mp than propane (C3H8).
d)
The stronger the particle interactions, the lower the viscosity of a liquid.
9)
For the following statements, agree or disagree and provide a justification for your answer:
a)
Solid sodium would be expected to be a worse conductor than solid NaCl.
b)
MgO would be expected to have a higher MP than butane (C4H10).
10)
In which of the following processes are covalent bonds broken?
11)
Which of the oxides listed below exists as a gas at 298 K and 1 atm?
Both CaO and K2O are ionic and therefore solids at room temperature. SiO2 is network covalent and is also a solid at room temp. NO2 however has LDF and is a gas.
12)
A pure liquid in an open vessel boils at the temperature at which the
This is the definition of boiling point: the temperature at which vapor pressure equals atomospheric pressure.
13)
On a mountaintop, it is observed that water boils at 90°C, not at 100°C as at sea level. This phenomenon occurs because on the mountaintop the
Boiling always happens when vapor pressure equals atmospheric pressure. On a mountain that just happens at lower temperatures because it doesn't take as much energy for the liquid to become a vapor when the atomospheric pressure is so much lower.
14)
CH3OH has a higher boiling point than C2H4. Which of the following statements provides the most likely explanation for this difference?
The molar masses are approximately the same, so the size of the LDF and polarizability is not a real issue with this pair.
15)
Which of the following are correctly ranked from highest to lowest freezing points?

In choice a., bromine should have the highest freezing point because all substances are LDF and bromine has the most electrons and is the most polarizable.

In choice b., the last two substances have LDF only and the last substance has fewer electrons so it should have the lowest freezing point. Between the firs two choices, the number of electrons are approximately the same but the first substance also has hydrogen bonding, so it should have the highest freezing point.

In choice c., all of the substances are metallic. Li is the smallest atom and so the electrons can get closer to the nucleus and it will take more energy to pull them away. K is the largest atom and so the electrons are more shielded from the nucleus so it will have the lowest freezing point of the three.

In choice d., MgO has +2/-2 charges which have greater electrostatic attractions than only +1/-1. This means that MgO should have the highest freezing point of the three substances. Between NaCl and LiF, Li and F are both smaller ions so they can be held closer together because the gained electrons are added closer to the nucleus. This means than LiF should have the higher freezing point compared to NaCl.