[KEY]REVIEW – Unit 5 Test (Chp 11,13): Bonds & IMAFs in Liquids, Solids, & Solutions

Stronger intermolecular forces will cause: (write higherorlower for each)

______boiling point______melting point______viscosity

______heat of fusion______heat of vaporization lowervapor pressure

(all others are higher)

1.Based on molecular mass and dipole moment of the five compounds in the table below, which one should have the lowest boiling point and why?

2.As a liquid element freezes, the atoms getcloser to/further fromeach other and

they have more/less attraction for one another.(circle each correct phrase)

3.The weakest interparticle attractions exist between particles inthegasstate and the strongest

interparticle attractions exist between particles in the solid state.

4.Of the following molecules, which has the largest dipole moment?

(A) CO(B) CO2(C) O2(D) HF(E) F2

5.Of the following substances, whichcan formhydrogen bonds?

CH3OHNH3H2SCH4HCl

6.Which one of the following exhibits dipole-dipole attractions between molecules?

CO2AlCl3H2OBr2XeF4

7.Which one of the following should have the highest boiling point?

NH3H2SHClSiH4H2O

8.Of the following, ______has the lowestheat of fusion.

9.The predominant intermolecular force in CH3CH2NH2 is hydrogen bonding.

10.The substance with the lowest heat of vaporization is ______.

11.Label each of the following as an endothermicor exothermic process.

  1. meltingendo
  2. freezingexo
  3. vaporizationendo
  4. sublimationendo
  5. condensationexo

12.A volatile liquid is one that easily vaporizes at lower tempsdue toweak IMAF’s.

13.Of the following, ______is the most volatile.

C2H6CCl4CCl2F2C4H10C6H6

14.During the phase changes B → C and D → E…

temperature is (circle one)increasing / decreasing / constant

kinetic energy is (circle one)increasing / decreasing / constant

potential energy is (circle one)increasing / decreasing / constant

Explain what the extra kinetic energy accomplishes between these points as the temperature is constant:

Added KE overcomes the IMAFs to cause more separation between molecules.

Name the phase change that is occurring between these points:

B → C meltingD → E vaporization

15.Molecular solids consist of atoms or molecules attracted by

A.dipole-dipole forces

B.London dispersion forces

C.hydrogen bonds

D.ANY of the above

E.NONE of the above

16.Amorphous solids differ from crystalline solids in that crystalline solids have organized repeated patterns of structure. (“a”“morphous” means “without” “form”)

17.Which statement(s) about viscosity is/are false?

(i)Viscosity increases as temperature increases.

(ii)Viscosity decreases as molecular weight increases.

(iii)Viscosity decreases as intermolecular forces decrease.

18.The property responsible for the "beading up" of water is surface tensionand increases with increasing IMAF’s.

19.High boiling and melting points in a substance are caused by stronger forces of attraction.

20.The vapor pressure of any substance is equal to 1 atmat its normal boiling point.

21.Ionicsolids are brittle with high melting points, and conduct electricity when molten or in solution.

22.X = CH3-CH2-CH2-CH2-CH3 Y = CH3-CH2-CH2-CH2-OH Z = HO-CH2-CH2-CH2-OH

Based on concepts of polarity and hydrogen bonding, which of the following sequences correctly lists the compounds above in the order of their increasing solubility in water?

(A) Z < Y < X

(B) Y < Z < X

(C) Y < X < Z

(D) X < Z < Y

(E) X < Y < Z

23.Explain why an egg takes longer to cook by boiling in Denver than in New York City.

The water boils at a lower temperature. There is a lower atmospheric pressure at higher altitudes so the water requires less energy (lower temperature) to make its vapor pressure equal to the lower atmospheric pressure to cause boiling.

(boiling – spontaneous phase change of liquid to gas when a liquid’s vapor pressure equals atmospheric pressure)

24.When a solution is formed by adding some methanol, CH3OH, to water, processes that are endothermic include which of the following?

  1. Methanol molecules move water molecules apart as the methanol goes into solution.
  2. Water molecules move methanol molecules apart as the methanol goes into solution.
  3. Intermolecular attractions form between moleculesof water and methanol as the methanol goes into solution.

(A)I only

(B)III only

(C)I and II only

(D)II and III only

25.Why do endothermic processes occur if they don’t release heat (enthalpy, H)?

Endothermic processes absorb heat (enthalpy, H)which raises the energy of a system (not favored), but they may also increase the entropy (dispersal) ofa system which lowers the overall energy of a system.

26.Which one of the following substances would be the most soluble in CH3COOH (ethanoic acid)?

  1. CBr4B. CH2Cl2C. C10H22D. H2OE. PH3

27.Which of the following choices has the compounds correctly arranged in order of decreasing solubility inwater? (most soluble to least soluble)

  1. CH4 > NH3 > CHCl3
  2. CH3OH > CCl4 > CHCl3
  3. LiF > NH3 > CHCl3
  4. CH3OH > CH4 > LiF
  5. CCl4 > CHCl3 > NH3

28.A sample of potassium chlorate (20.0 g) is dissolved in 99 g of water at 70 °C, with precautions taken to avoid evaporation of any water. The solution is cooled to 20.0 °C and white crystalline precipitate is observed. Describe and characterize the current solution as saturated, unsaturated, or supersaturated.

The solution is saturated (some solute could not dissolve). The solute is in a dynamic equilibrium (continues to dissolve and precipitate out at equal rates) so that there is no net change in the amount of solute in solution.

29.Define a supersaturated solution. Describe a simple test and the expected results to identify a solution as supersaturated, saturated, or unsaturated.

A supersaturated solution contains more solute that it can typically hold at that temperature.

The seed crystal test: Add solute particles to the solution; if it’s supersaturated,all of the extra solute will crystallize out of solution; if it’s saturated, the added solute will not dissolve; if it’s unsaturated, the added solute will dissolve.

30.The concentration of potassium ion in a solution that contains 0.500 M potassium sulfate is1.00M.

31.As the intermolecular attractions of liquidsdecrease, the vapor pressure of liquids increase causing theboiling point of liquids todecrease.

32.A closed rigid container contains water and N2(g) at equilibrium. Actions that would increase the concentration on N2(g) in the water include which of the following?

I. Shaking the container vigorously

II. Raising the temperature of the water

III. Injecting more N2(g) into the container

(A) I only(B) II only(C) III only(D) I and II only(E) I, II, and III

33.Which of the following has the lowest conductivity? Which has the highest conductivity?

(A) 0.1 M CuSO4

(B) 0.1 M KOH

(C) 0.1 M BaCl2

(D) 0.1 M HF

(E) 0.1 M HNO3

Element / Metallic Radius (pm) / Melting Point (oC) / Common Oxidation State
Au / 144 / 1064 / 1+ , 3+
Cu / 128 / 1085 / 1+ , 2+
Ag / 144 / 961 / 1+

34.To make Au stronger and harder, it is often alloyed with other metals, such as Cu and Ag.

Consider two alloys, one of Au and Cu and one of Au and Ag, each with the same mole fraction of Au. If the Au/Cu alloy is harder than the Au/Ag alloy, then which of the following is the best explanation based on the information in the table above?

(A) Cu has two common oxidation states, but Ag has only one.

(B) Cu has a higher melting point than Au has, but Ag has a lower melting point than Au has.

(C) Cu atoms are smaller than Ag atoms, thus they interfere more with the displacement of atoms in the alloy.

(D) Cu atoms are less polarizable than are Au or Ag atoms, thus Cu has weaker interparticle forces.

[KEY]REVIEW Unit 5 Test Chp 11,13: Intermolecular Attractive Forces, Liquids, Solids, Solutions

Section II Free Response

Calculator Allowed

CLEARLY SHOW THE METHODS USED AND STEPS INVOLVED IN YOUR ANSWERS.

It is to your advantage to do this, because you may earn partial credit if you do and little or no credit if you do not. Attention should be paid to significant figures.

  1. Answer each of the following in terms of principles of molecular behavior and chemical concepts.

(a)The structures for benzene, C6H6, and nitroglycerin, C3H5N3O9, are shown below.

Identify the type(s) of intermolecular attractive forces in

(i)pure benzene (1)London dispersion forces

(ii)pure nitroglycerin (1)London dispersion forces and dipole-dipole interactions

(b)Nitroglycerin is soluble in water but benzene is not soluble in water. Explain. (2)

Benzene is nonpolar has only London dispersion forces and is therefore not soluble in a polar solvent like water. Nitroglycerin has dipole-dipole forces and will attract water molecules thereby making it dissolve (or solvate) in water.

(c)Indicate whether you agree or disagree with the statement in the box below. Support your answer with a short explanation. (1)

Disagree b/c boiling is a physical process (not chemical) involving only the separation of molecules by overcoming the IMAF’s to break intermolecular bonds (not covalent intramolecular bonds) so the water molecules remain intact.

2.The condensed structural formulas of methylamine and ethane are shown below.

CH3NH2 CH3CH3

Methylamine Ethane

(a)In the table, write the type(s) of intermolecular attractive force(s) that occur in each substance. (2)

Substance / Boiling Point / Intermolecular Attractive Force(s)
Methylamine / 267.2K / London dispersion forces, dipole-dipole interactions, hydrogen bonding
Ethane / 184.5 K / London dispersion forces

(b)Use principles of intermolecular attractive forces to explain why ethane has a lower boiling point than methylamine. (1)

Ethane has only dispersion forces but methylamine has dipole-dipole and hydrogen bonding. Therefore, methylamine has stronger intermolecular attractive forces and requires more kinetic energy to overcome them creating enough separation to become a gas. More kinetic energy required yields a higher boiling point than that of ethane.

Answer the following questions related to a compound of sulfur, H2S .

(c)Two types of intermolecular forces present in liquid H2S are London dispersion forces and dipole-dipole forces.

(i)Compare the strength of the London dispersion forces in liquid H2S to the strength of the London dispersion forces in liquid H2O. Explain. (1)

The strength of the London forces in liquid H2S is greater thanthat of the London forces in liquid H2O. The electron cloud ofH2S has more electrons and is thus more polarizable than theelectron cloud of the H2O molecule.

(ii)Compare the strength of the dipole-dipole forces in liquid H2S to the strength of the dipole-dipole forces in liquid H2O. Explain. (1)

The strength of the dipole-dipole forces in liquid H2S isweaker than that of the dipole-dipole forces in liquidH2O. The net dipole moment of the H2S molecule is lessthan that of the H2O molecule. This results from the lesserpolarity of the H–S bond compared with that of the H–Obond (S is less electronegative than O so there is a smaller difference of electronegativity between H–S than H–O).

  1. Account for each of the following observations about pairs of substances. In your answers, use appropriate principles of chemical bonding and/or intermolecular forces. In each part, you must include references toboth substances.

(a)MgO melts at a much higher temperature (2,852oC) than NaF (993oC). (2)

MgO and NaF are both ionic solids. The +2 and 2 charges in MgO result in a greater attraction between ions than the +1 and 1 charges in NaF. More energy is required to break the stronger ionic bonds.

(b)Si melts at a much higher temperature (1,410oC) than Cl2 (–101oC). (2)

Si is a network covalent solid with strong covalentbonds between atoms. Cl2has weak London dispersion forces between the molecules. Therefore, more energy is required to break the stronger bonds of Si than the weak intermolecular forces of Cl2.

(c)At 25C and 1.0 atm, ethane (C2H6) is a gas and hexane (C6H14) is a liquid. (2)

C2H6 and C6H14 both have London dispersion forces. The forces between C6H14molecules are stronger because the molecule has a larger electron cloud that is more polarizable.

(d)Structures of the dimethyl ether molecule and the ethanol molecule are shown below. The normal boiling point of dimethyl ether is 250 K, whereas the normal boiling point of ethanol is 351 K. Account for the difference in boiling points. (2)

(e)Ammonia, NH3, is very soluble in water, whereas phosphine, PH3, is only moderately soluble in water.(2)

Ammonia has hydrogen bonding intermolecular attractive forces (IMAFs), whereas phosphine has dipole-dipole interactions. Water also has hydrogen bonding IMAFs. Ammonia is more soluble in water than phosphine because ammonia molecules can have more similar IMAFs with water (can form hydrogen bonds) than phosphine. Phosphine does dissolve moderately well in water due to common dipole-dipole interactions, but is not as strongly attracted to water as ammonia is by hydrogen bonding.

  1. The structures of a water molecule and a crystal of LiCl(s) are represented above. A student prepares a 1.0 M solution by dissolving 4.2 g of LiCl(s) in enough water to make 100 mL of solution

(a)In the space provided below, show the interactions of the components of LiCl(aq) by making a drawing thatrepresents the different particles present in the solution. Base the particles in your drawing on the particlesshown in the representations above. Include only one formula unit of LiCl and no more than ten moleculesof water. Your drawing must include the following details. (2)

• identity of ions (symbol and charge)

• the arrangement and proper orientation of the particles in the solution

(b)The solvation of LiCl in water is an endothermic process. Describe the relative strengths of solute-solute, solvent-solvent, and solute-solvent attractions that are formed and broken in the solvation process of LiCl in water.

The separations Li+ and Cl– and H2O---H2O are endothermic.

The formation of ion-dipole attractions of Li+ and Cl– with H2O are exothermic.

Since the overall process is endothermic, the solute-solute and solvent-solvent attractions must be stronger than the solute-solvent attractions. (but the solution forms anyway b/c it increases the entropy of the system)

Answer Key

1.2006#6

2.(a)2005B#8(d)

2.(b)2005B#8(e)

2.(c)2009#6(d)

3.(a)2001#8(d)

3.(b)2001#8(c)

3.(c)2001#8(b)

3.(d)2008#6(b)

3.(e)2004#7(d)

4.(a)2013#6(a)

4.(b)(created)

1