AP Chem Test 3A

Topics 3.1 to 3.6

Pentane, C5H12 and Octane C8H18, are both hydrocarbons.

a) Identify the type of intermolecular forces present.

b) Predict the substance that would have a higher vapor pressure and justify your claim.

Pentane, C5H12 and Octane C8H18, are both hydrocarbons.

a) Identify the type of intermolecular forces present.

b) Predict the substance that would have a higher vapor pressure and justify your claim.

a) Both molecules would only exhibit London Dispersion Forces (LDF). (Both are made up from C-H and C-C which have negligible electronegativity differences.)

b) C5H12 would have higher vapor pressure. C5H12 is less polarizable than C8H18 as it has fewer electrons, meaning that the IMF is weaker. Weaker IMF means that it vaporizes more readily resulting in a higher vapor pressure.

The boiling point of HF is 293 K whereas the boiling point of F2 is 85 K.

a) Determine the type(s) of intermolecular forces present.

b) Explain the difference in boiling points based on their intermolecular forces.

a) HF- LDF, dipole-dipole, H-bond, strong IMF

F2- LDF, weak IMF

b) Strong IMF means higher BP

In each pair decide which would have a lower boiling point. Explain why.

a) He or Ne

b) CH4 or CCl4

c) CF4 or CF3H

d) NH3 or PH3

a) He- lighter

b) CH4- smaller and simple, is a gas

c) CF4- no dipole moment

d) PH3- no hydrogen bond

1-Butanol and diethyl ether are structural isomers, meaning they have the same formula but the atoms are arranged differently.

a) Identify the intermolecular forces present in each.

b) Justify the difference in their boiling points.

a) both have London and dipoles, only butanol has h-bond

b) H-bond is stronger, diethyl has a weak dipole

Place the following in order of increasing boiling point.

C3H8, He, CH3OH, HOCl2OH, HCl

He, C3H8, HCl, CH3OH, HOCH2OH

Which of the following would have the strongest ion-dipole interaction with water? Explain.

Tl3+, Cd2+, Na+

Tl3+ has the highest charge because of its stronger electrostatic attraction and intramolecular forces.

Circle the molecules that are capable of hydrogen-bonding with another of the same molecule?

a) H2S

b) HCl

c) C5H12

d) CH3OH

e) NCl3

f) CH3NH2

For all of the molecules that exhibit hydrogen bonding, draw the two molecules and use a dotted line to indicate the hydrogen bond.

d) CH3OH and f) CH3NH2

Pentane has 3 isomers: Use the structures to place them in order of increasing intermolecular forces.

1) Pentane 2) Isopentane 3) Neopentane

1) Neopentane 2) Isopentane 3) Pentane

Long thin molecules have most IMF

Use intermolecular forced to explain why the vapor pressure of CH4 is greater than that of NH3. (both at room temperature)

CH4 has LDF and has higher vapor pressure because less IMF and is nonpolar. It does not stick very well to other CH4 so easily becomes a vapor. NH3 has LDF, dipole, and H-bond.

The amount of energy needed to melt a substance at its melting point is called the heat of fusion and for eager the value is 6.01 kJ/mol. The amount of energy needed to vaporize a substance at its boiling point is called the heat of vaporization and for water the value is 40.7 kJ/mol. Use the relative distances in the states of matter and the concepts of intermolecular forces to explain the difference.

Ice to liquid; distance increases, H-bond to H-bond

Liquid to gas; distance REALLY increases, H-bond to no attraction, breaks all H-bonds, need more energy to do that

CO2 melts at -78 C and SiO2 mys at 1650 C.

a) Identify the type of solid each substance forms.

b) Justify the difference in melting points.

a) CO2 is a molecular solid and SiO2 is a covalent network.

b) CO2 is a molecular solid therefore when it melts only IMFs are being broken. These are the weakest forces so very little energy is required to my which results in a very low boiling point. SiO2 is a covalent network solid therefore when it melts covalent bonds must be broken. Covalent bonds require a large amount of energy to be broken which results in a very high boiling point.

Classify Cl2, Ni, BN, and FeS as ionic, molecular, covalent network, or metallic solids and arrange them in order of increasing melting points.

Cl2- molecular (-101 C), FeS- ionic (1194 C), Ni- metallic (1455 C), BN- covalent network (2973 C)

Match the following descriptions with one of the four types of solids:

For each type of solid, indicate the type of attractive forces that are broken upon melting, and describe the individual particles that makes sense up the resulting liquid.

The binding forces in each solid are responsible for certain properties associated with each type of solid.

Explain why covalent network solids melt St a much higher temperature than molecular solids.

Covalent networks need large energy to break covalent bonds, whereas molecular only have LDF, dipole, and it takes less energy to overcome.

What type of solid will each of the following substances form?

a) CH4

b) I2

c) graphite

d) KCl

e) C6H12O6

f) CaBr2

g) SiC

h) Au

a) molecular

b) molecular

c) covalent network

d) ionic

e) molecular

f) ionic

g) covalent network

h) metallic

The melting point of HBr is -87 C and the melting point of NaBr is 747 C.

a) Identify the type of solid in each substance

b) Justify the difference in their melting points.

a) HBr is a molecular solid and NaBr is ionic.

b) HBr has LDF, dipole, easier to break, partial charge. NaBr has full charge on ions and is very strong.

Of the following, the best explanation for the fact that most liquids cannot be easily compressed is that the molecules in a liquid:

b) are relatively close together

Particles are close together so not easily compressed, this results in a fixed volume.

Draw a particle diagram to represent water in a puddle as if starts to evaporate.

Sand is primarily silicon dioxide, SiO2.

a) Draw a particle diagram of solid sand.

b) Draw a particle diagram of sand mixed with liquid water. Make sure to represent the states of each.

The triple point is the set temperature and pressure where a substance occurs as a solid, liquid, and gas simultaneously at equilibrium. For water, this occurs ag 273.16 K and 0.6117 kPa. Draw a set of particle diagrams to represent this point.

Which of the following is the best explanation for why gases generally follow the ideal gas law?

c) Gas particles are spaced far apart with minimal intermolecular forces.

Or almost non-existent

Molten iron and solid iron occupied almost the same volume. The density of molten iron, Fe, is 6.98 g/mL while solid iron had a density of 7.874 g/mL. Draw a particle diagram for both; be sure to account for the differences.

Gases ten to be more ideal when the pressure is low and the temperature is high. Draw two particle level diagrams that help to explain this phenomenon.

When heated strongly, solid calcium carbonate decomposes to produce solid calcium oxide and carbon dioxide gas, as represented by the equation above. A sample of CaCO3 (s) is placed in a rigid 35 L reaction vessel from which all the air has been evacuated. The vessel is heated to 437 C at which time the pressure of CO2 (g) in the vesske is constant at 1.00 atm. Calculate the number of grams of CaCO3 (g) that reacted ti produce the carbon dioxide gas.

A basketball is left outside in winter when the temperature is -2.00 C, has a volume of 6.88 L and the pressure inside the basketball is 0.795 atm. How many moles of gas are in a basketball? What is the partial pressure of oxygen in the basketball?

A gas mixture at 20.0 C and 2.0 atm contains 0.40 mol of H2, 0.15 mol of O2, and 0.50 mol of N2. Assuming ideal behavior, what is the partial pressure of hydrogen gas (H2h in the mixture?

193 mL of oxygen, O2, was collected over water on a day when the atmospheric pressure was 762.0 mmHg. The temperature of the water was 23.0 C. (At 23.0 C the vapor pressure of water is 21.1 mmHg)

a) What is the partial pressure of the oxygen gas collected?

b) How many moles of oxygen were collected?

c) How many grams of oxygen were collected?

An ideal gas sample has a mass of 1.28 grams in a 0.500 L container. The temperature of the container is 127 C and the pressure of the gas is 2.00 atm. What is the molar mass of the gas?

Given the following reaction: How many liters of gaseous oxygen are needed to produce 6.50 L of gaseous nitrogen dioxide, if both gases are being measured at STP?

Volume ratio = stoichiometric ratio at STP

Ratio = 1:2, 6.50 L/2 = 3.25 L

Air at 30,000 feet is at a temperature of -35.0 C. A sample of air was collected and the mixture is 78.0% nitrogen, 21.0% oxygen and 1.0% argon (percentages are by mass). If 0.594 moles of air are captured in a 45.0 L container from a plane flying at 30,000 feet:

a) Calculate the total pressure in the container.

b) Calculate the partial pressure of each gas.

How many grams of potassium chlorate, KClO3, were reacted if 5.30 liters of oxygen, O2, were produced at 117 C and 0.995 atm?

What is the density if NO2 gas at 25.0 C and 2.56 atm?

By what factor will the pressure if a sample of a gas change if the volume is reduced by 1/3 while the Kelvin temperature is doubled?

What is the final pressure in the container shown below after the valve is opened and the gases arekwed to flow? (The gases do not react)

Consider an equimolar mixture of gases, H2, N2, and F2 placed into container with a pinhole opening. After some time has passed, place the gadrs in order of increasing amount remaining in the container.

H2 (fastest), N2, F2 (slowest)

A 1 L vessel containing 1 mole of H2 at 200. K is shown below. Draw the following:

Equimolar samples of N2 and O2 are both at standard conditions (1 atm, 273 K).

a) Which eamlme has more kinetic energy? Why?

b) Which sample has higher average molecular speeds? Why?

a) Both at same temperature and atm, so KE is the same.

b) N2 because less mass.

Place the following gases in order of increasing kinetic energy.

Gas C, Gas A, Gas B

A Maxwell-Boltzmann Distribution is shown: on the following graphs, sketch the changes specified.

Two cases are placed at either end of a tube at room temperature as shown; when they meet a white/yellow precipitate will form. Where in the tube do you predict to see the precipitate?

A sample of nitrogen monoxide, NO, was placed in a sealed, rigid, container at 200. K. The vessel was heated to 400. K. What changes will occur and why?

Volume will have no change, temperature will increase, pressure will increase, moles will have no change, and speed will increase.

At 10. atm and 100 K, radon (Rn) deviates from its predicted volume based on the ideal gas law.

a) If radon bad a smaller volume than predicted, propose an explanation to justify this observation.

b) If radon has a larger volume than predicted, propose an explanation to justify this observation.

a) The IMF is strong and pulls the particles closer together resulting in a decrease in volume

b) The particles occupy space and the volume of the particles increases the volume

Sample 1 and Sample 2 represent the same gas at 298 K. Identify the gas that is more likely to deviate from ideality and justify your selection.

Sample 2 is more likely to deviate because more IMF from being closer together.

NO2 and CO2 have a similar molecular weight. Which gas would you predict to deviate from an ideal gas? Justify your selection.

NO2 is polar and has a strong dipole moment so more IMF than CO2 = less ideal.

Choose a set of conditions (high/low) for each of the following: