cdo ap chemistry unit 7 part 1 problem set imf, solids...

CDO AP Chemistry Unit 7 Part 1 Problem Set IMF, Solids and Liquids

VIDEO 1 1. For each pair of compounds listed below, identify the compounds intermolecular forces and determine

which of the pair has the higher boiling point.

a. Br2 or I2 Both have London dispersion forces, I2 is larger and has more electrons than Br2 making it more polarizable than I2, thus the LDF in I2 are more significant and I2 will have a higher boiling point

b. NH3 or NCl3 NH3 had London Dispersion, Dipole-Dipole and Hydrogen Bonds. NCl3 has London Disperion and Dipole Dipole. Hydrogen Bonds is a stronger force of attraction than the Dipole Dipole so NH3 has the higher boiling point.

c. NH3 or CH4 NH3 had London Dispersion, Dipole-Dipole and Hydrogen Bonds. CH4 has only London Dispersion, Hydrogen Bonds is a stronger force of attraction than the London Dispersion so NH3 has the higher boiling point.

d. CH4 or CCl4 Both have only London Dispersion, CCl4 is larger and has more electrons than CH4 making it more polarizable than CH4, thus the LDF in CCl4 are more significant and CCl4 will have a higher boiling point

e. He or Ar Both have only London Dispersion, Ar is larger and has more electrons than He making it more polarizable than He, thus the LDF in Ar are more significant and Ar will have a higher boiling point

f. Cl2 or H2 Both have only London Dispersion,Cl2 is larger and has more electrons than H2 making it more polarizable than H2, thus the LDF in Cl2 are more significant andCl2 will have a higher boiling point

g. H2O or H2S H2O had London Dispersion, Dipole-Dipole and Hydrogen Bonds. H2S has London Dispersion and Dipole Dipole. Hydrogen Bonds is a stronger force of attraction than the Dipole Dipole so H2O has the higher boiling point.

h. CH4 or SnH4 Both have only London Dispersion, SnH4 is larger and has more electrons than CH4

making it more polarizable than CH4, thus the LDF in SnH4are more significant and CH4 will have a higher boiling point

i. NH3 or PH3 NH3 had London Dispersion, Dipole-Dipole and Hydrogen Bonds. PH3 has London Dispersion and Dipole Dipole. Hydrogen Bonds is a stronger force of attraction than the Dipole Dipole so NH3 has the higher boiling point.


j. AsH3 or SbH3 Both have only London Dispersion and Dipole Dipole , SbH3 is larger and has more electrons than AsH3 making it more polarizable than AsH3, thus the LDF and Dipole Dipole in SbH3

are more significant and AsH3 will have a higher boiling point

k. Ca(OH)2 or H2O H2O has London Dispersion, Dipole-Dipole and Hydrogen Bonds. Ca(OH)2 has ionic bonds. Ionic bonds are stronger than Hydrogen bonds, making Ca(OH)2 having the higher boiling point

l. KCl or Cl2 Cl2 has London Dispersion. KCl has ionic bonds. Ionic bonds are stronger than Hydrogen bonds, making KCl having the higher boiling point

m. F2 or Cl2 Both have only London Dispersion,Cl2 is larger and has more electrons than F2 making it more polarizable than F2, thus the LDF in Cl2 are more significant and Cl2 will have a higher boiling point

n. C2H6 or C4H10 Both have only London Dispersion, C4H10 is larger and has more electrons than C2H6 making it more polarizable than C2H6, thus the LDF in C4H10 are more significant and C4H10 will have a higher boiling point

2. Explain why Cl2 is a gas and Br2 is a liquid at 25oC and 1 atm. Both are non polar and have only London Dispersion Forces. Bromine is larger and has more electrons than Chlorine which makes it more polarizable. The stronger dispersion forces causes the molecules to be close together making it a liquid

3. Explain why H2 is a gas and I2 is a solid at 25oC and 1 atm.

Both are non polar and have only London Dispersion Forces. Iodine is larger and has more electrons than Hydrogen which makes it more polarizable. The stronger dispersion forces causes the molecules to be close together making Iodine a solid at room temp

4. Explain why ethane, C2H6, melts at -183oC and nonane, C9H20 melts at -54oC

Both are non polar and have only London Dispersion Forces. Nonane is larger and has more electrons than Ethane which makes it more polarizable. The stronger dispersion forces in nonane require more energy to be overcome, so the higher melting point

5. Explain why propane, C3H8 , is a gas and decane, C10H22, is a liquid at 25.0oC and 1 atm.

Both are non polar and have only London Dispersion Forces. Decane is larger and has more electrons than Propane which makes it more polarizable. The stronger dispersion forces causes the molecules to be close together making it a liquid


6. Draw the Lewis structures for ethanal, C2H4O, and methanol, CH3OH.

a. Identify the types of intermolecular forces that exist in pure ethanal.

b. Identify the types of intermolecular forces that exist in pure methanol.

VIDEO 2 7. Draw the Lewis structures for aminopropane, CH3CHNH2CH3, and isobutane, C4H10.

a. Identify the types of intermolecular forces present in pure aminopropane

b. Identify the types of intermolecular forces present in pure isobutene.

c. Which liquid has the highest boiling point? Explain


8. Explain why the standard enthalpy of vaporization, Hvap, values for each set of compounds below are not the same.

a. CH4 and H2O

Methane has London dispersion Water has London dispersion, dipole/dipole and hydrogen bonding

The differences in IMF would account for different Hvap b. PH3 and NH3

Both have London dispersion and dipole/dipole, ammonia also has hydrogen bonding. The

differences in IMF would account for different Hvap c. C2H6 and C3H8

Both have London dispersion, Propane has a larger molar mass, the difference in molar mass would

account for the different Hvap d. BH3 and OF2

Both have London dispersion OF2 also has dipole/dipole, The differences in IMF would account for

different Hvap

9. Identify the types of intermolecular or intramolecular forces that are involved in each of the following processes, and describe what happens to these forces while the processes are occurring.

a. CO2(s) CO2(g)

Phase change, physical change, making the molecules move further apart, causing the IMF to be overcome (London dispersion)

b. CO2(g) C(s) + O2(g) Chemical change, the covalent bond between C and O is broken

c. NH2F(l) NH2F(g) Phase change, physical change, making the molecules move further apart, causing the IMF to be overcome (London dispersion, dipole/dipole, hydrogen bonding)

d. NH2F(l) 1/2N2(g) + H2(g) + 1/2F2(g) Chemical change, the covalent bonds between N, H and F are broken

e. H2O(s) H2O(g) Phase change, physical change, making the molecules move further apart, causing the IMF to be overcome (London dispersion, dipole/dipole, hydrogen bonding)

10. Explain why the temperature of a liquid remains constant while it is being boiled, although heat continues to be absorbed. Describe what happens to the heat that is absorbed.

The temperature stays constant because the energy being added is going into moving the particles further apart so the phase change can happen, the IMF forces are being broken

11. Explain why the boiling point of water decreases as elevation increases. A liquid boils when the vapor pressure equals the atmospheric pressure. At higher altitudes the pressure is lower so it takes less energy to reach the point in which the two are equal.


VIDEO 3 12. The following graph shows the plot of temperature versus time as heat is added to a pure substance.

a. During what period of time is the substance at its normal freezing point?

About1.3-3.0min b. Over what period of time was the substance boiling?

From 5-7 min c. What is happening to the substance between the 1 and 1.5 minute marks?

It’s a solid, the avg KE of the molecules is increasing d. What is happening to the substance between the 2 and 3 minute marks?

Its going through a phase change, the KE of the molecules stays the same where the distance between the molecules is increasing and the IMF are weakening

e. What is happening to the substance between the 3.5 and 4.5 minute marks? It’s a liquid and the avg KE of the molecules is increasing

f. What is happening to the substance between the 5 and 7 minute marks? Its going through a phase change from a liquid to a gas. The KE of the molecules is staying the same but the IMF are becoming weaker and the distance between the molecules is increasing

13. Consider the phase diagram of a pure substance shown below.

a. What happens to the substance if the temperature increases from 20oC to 40oC at a constant pressure of 0.3 atm. Starts as a solid then reaches the sublimation curve where the solid and liquid are at equilibrium and then it turns into a gas

b. What happens to the substance if the temperature increases from 20oC to 40oC at a constant pressure of 2.0 atm. The substance is a solid then reaches the solid liquid line where both the solid and liquid phase are at equilibrium, then as the temp approaches 40 its only a liquid

c. What happens to the substance if the temperature decreases from 120oC to 60oC at a constant pressure of 2.0 atm. Starts as a gas, then reaches equilibrium between a gas and a liquid, then becomes only a liquid

d. What happens to the substance if the pressure increases from 0.2 atm to 1.5 atm at a constant temperature of 60oC. Starts as a gas, then reaches equilibrium between a gas and a liquid, then becomes only a liquid

e. What happens to the substance if the pressure decreases from 2.5 atm to 1.0 atm at a constant temperature of 35oC? Starts as a solid, then reaches the solid liquid line and the two phases are in equilibrium, the it is only a liquid

f. Are there conditions under which the solid phase of this substance can be liquefied by increasing the pressure? Justify your answer. Yes, because this substance has a negative slope between the two phases


g. At what temperature and pressure are the solid liquid, and gaseous phases of this substance in equilibrium with one another? What is this point on the graph referred to? 40oC and 0.7 atm, it is called the triple point

h. Beyond what temperature and pressure do the liquid and gaseous phases of this substance

become indistinguishable from one another? What is this point on the graph referred to as? 120oC and 2.6 atm, critical point

14. Dry ice (solid carbon dioxide) appears to change from solid to gas phases without going through the liquid

phase on the stage at a rock concert. Explain why this is. At 1 atm pressure CO2 doesn’t have a liquid phase according to the phase diagram for CO2, at 1 atm it sublimes

15. Why do the liquid and solid phases of a pure substance become indistinguishable from one another beyond the critical point?

The density of the gas increases because the concentration of the gas is increasing as it is getting hotter and the density of the liquid is decreasing as it is getting hotter, at the critical point these densities are becoming equal so the phases are indistinguishable from one antoher.

16. Is the vapor pressure of a liquid greater than, equal to, or less than that of its solid at the triple point? They are equal at the triple point since all the phases are at equilibrium at this point

17. What is a supercritical fluid? What conditions are necessary in order to produce a supercritical fluid? It is the phase that exists beyond the critical point. It is where temperature and pressure exceeds the critical point

VIDEO 4 18. Which of the following structures is most likely to be a solid at room temperature? Justify your answer in

terms of intermolecular interactions. Structure A will most likely be a solid at room temperature. They are both about the same size with the

same IMF (Hydrogen bonds at one end) Structure A however doesn’t have a double bond in the middle like

Structure B does which means that there is a “kink” in structure B which will cause multiple molecules of

structure B to stay further apart than Structure A. Since molecule of structure A can stack closer together

the substance will be a solid at room temp.

19. What are the main factors that account for the extreme hardness of diamond? Diamond is a network covalent solid with a tetrahedral geometry of C atoms around each C atom


20. Create a visual representation of a metallic solid that can be used to explain the electron sea model of metallic bonding. Use that representation to help you explain the factors that make metals good conductors of heat and electricity. The delocalized “Sea” of electrons, the free movement of electrons accounts for the heat and electrical conductivity, with heating the electrons are also moving faster.

21. Which substance in each set has the highest melting point? Justify your answer using chemical principles.

a. KCl or SiO2 – KCl contains ionic bonds and SiO2 has network covalent bonds, network covalents are a strong force so it will have a higher melting point.

b. NH3 or Cdiamond – NH3 contains dispersion, dipole/dipole and hydrogen bonding where diamond has network covalent bonds, network covalents are a strong force so it will have a higher melting point.


22. The following questions pertain to silicon semiconductors.

a. Explain why silicon is a poor conductor of electricity at room temperature. Create an energy level

diagram that shows the valence and conducting bands associated with silicon’s molecular orbitals to

help with your explanation.

Si has two bands of conductivity the valence band and the conduction band. The valence band has the

lower energy MO’s and the conduction band contains the higher energy MO’s. There is any energy gap

between these bands. Valence electrons must be promoted to the conduction band in order for

electricity to be conducted. Si has a large energy gap and few valence electrons have enough energy to

jump the gap

b. Explain why silicon is able to conduct electricity better at higher temperatures.

As temperature increases more electrons are able to jump the energy gap

c. What is an n-type semiconductor and explain how it improves the conductivity of silicon. Create a

diagram to help with your explanation.

An n-type semiconductor is one the is doped by a small amount of a group V element, since group 5

elements have one more valence electron than Si, the extra electron can occupy empty MO’s closer to

the conduction band so less energy is required for the electron to reach the band.

d. What is a p-type semiconductor and explain how it improves the conductivity of silicon. Create a

diagram to help with your explanation.

A p-type semiconductor is one that is doped with a group III element. Group III elements have one less

electron than Si which leaves unfilled MO’s in the valence band. Conductivity increases because

electrons can migrate to these positive holes which actually will leave holes causing more electron

migration, this allows for a better flow of electricity

e. What is a p-n junction and explain how it is able to convert alternating current into pulsating direct

current. Create diagrams to help with your explanation.

A p-n junction occurs when a p-type and n-type semiconductors are connected. This causes electrons to flow in only one direction turning AC current into DC current


23.

a. Which of the three saturated solutions above would produce the greatest mass of precipitate when cooled from 90oC to 60oC? KClO3 b. The molarity of which solutions would increase by the greatest degree when it is cooled from 20oC to 0oC?

Cd(SO4)3 24. Explain how solutes can be separated through paper chromatography based on intermolecular forces. In Paper chromatography the bottom of paper (stationary phase) is placed in a solution (mobile phase). The solution moves up the paper is capillary action. As the solvent moves up the paper it takes solute particles with it. The paper is both polar and non polar solutes that are the most polar will be attracted to the polar sections of the paper. Usually the solvent is non polar. If there are strong IMF’s between the solvent and solute it will travel up the paper, weak attractions come off early. 25. Fractional distillation was used to isolate an unknown volatile substance that had contaminated the well water at a rural property.

a.Is the boiling point of the unknown substance greater than, less than, or equal to 100oC at 1.0 atm? Justify your answer. Less than 100, in order for it to be isolated it must have a lower bp than water b.What can be said about the relative strengths of intermolecular interactions among and between the components in question (contaminant and water)? The attraction for water for itself must be greater than the attraction between the water and the contaminant molecules. Otherwise it would have not separated from the water.

26. The following questions pertain to a pure sample of iron and a sample of steel. a. Create an illustration of pure iron which shows the iron atoms and provides a visual

representation of the electron sea model.

b. Create a representation of steel that shows the iron and carbon atoms. c. In what way have some of the bonds changes when this alloy was formed?


d. What type of alloy is steel? e. Identify four properties that change when carbon is added to pure iron in order to make

steel. f. Explain how carbon changes the properties outlined in part e.

cdo ap chemistry unit 7 part 1 problem set imf, solids...

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