AP Chemistry - Problem Drill 15: Liquids and Solids

Question No. 1 of 10 Instruction: (1) Read the problem statement and answer choices carefully (2) Work the problems on paper as needed (3) Pick the answer (4) Go back to review the core concept tutorial as needed. 1. The physical properties of melting point, boiling point, vapor pressure, evaporation, viscosity, surface tension, and solubility are related to the strength of attractive forces between . These attractive forces are called intermolecular forces. There are four types of intermolecular forces. What intermolecular forces does H2O exhibit?

A. London Dispersion Forces Question B. Dipole-Dipole Forces C. Hydrogen Bonding D. All of the above

A. Incorrect. Water does have London Dispersion Forces, but there are also other intermolecular forces.

B. Incorrect. Water does have Dipole-Dipole Forces, but there are also other intermolecular forces.

C. Incorrect.

Feedback Water does have Hydrogen Bonding Forces, but there are also other intermolecular forces.

D. Correct! Good job! Water does have London Dispersion Forces, but there are also other intermolecular forces.

ll molecules exhibit London Dispersion Forces. Water is a polar with two hydrogen bonded to a highly electronegative (oxygen). The asymmetrical distribution of lone pair electrons of oxygen combines with the asymmetrical distribution of the polar H-O bonds to give the water molecule a dipole, while polar H-O bonds enable hydrogen bonding.

Solution The correct answer is (D).

RapidLearningCenter.com  Rapid Learning Inc. All Rights Reserved Question No. 2 of 10 Instructions: (1) Read the problem and answer choices carefully (2) Work the problems on paper as needed (3) Pick the answer (4) Go back to review the core concept tutorial as needed. 2. Pressure is the average force that materials (, liquid or solid) exert upon the surface, e.g. walls of a container or other confining boundary. Vapor pressure is the pressure of a vapor in thermodynamic equilibrium with its condensed phases in a closed container. All liquids and solids have a tendency to evaporate into a gaseous form, and all have a tendency to condense back to their liquid or solid form. How is vapor pressure affected by an increase of temperature?

Question (A) Vapor Pressure increases. (B) Vapor Pressure decreases. (C) Vapor Pressure remains the same. (D) There is not predictable pattern.

A. Correct! Good job! As temperature increases, the number of atoms with the minimum energy to vaporize increases.

B. Incorrect. As temperature increases, the number of atoms with the minimum energy to vaporize increases.

C. Incorrect.

Feedback As temperature increases, the number of atoms with the minimum energy to vaporize increases.

D. Incorrect. As temperature increases, the number of atoms with the minimum energy to vaporize increases.

Vapor pressures are dependent only on temperature and nothing else. The vapor pressure of a liquid does not depend on the amount on the liquid in the container, be it one liter or thirty liters; at the same temperature, both samples will have the same vapor pressure.

As temperature increases, the number of atoms with the minimum energy to vaporize increases. Vapor pressure increases.

Solution The correct answer is (A).

RapidLearningCenter.com  Rapid Learning Inc. All Rights Reserved Question No. 3 of 10 Instructions: (1) Read the problem and answer choices carefully (2) Work the problems on paper as needed (3) Pick the answer (4) Go back to review the core concept tutorial as needed. 3. Hydrogen bonding can be formed intra- and intermolecularly, in the form of R- X-H …. X-R’, when a highly electronegative atom X such as F, O or N is bonded to a hydrogen atom. Hydrogen bonds tend to be stronger forces than dipole-dipole attractions between polar molecules. Which of the following molecules is likely to form an intermolecular between themselves?

(A) C6H5NO2 Question (B) CH3OH (C) CO2 (D) CH3F

A. Incorrect.

Nitrobenzene with –NO2 group has the electronegative atom N and O, but it does not have a hydrogen attached to an electronegative atom in order to form a hydrogen bond.

B. Correct! Good job! Methanol has the electronegative atom O with two lone pairs and a hydrogen atom directly attached to it (hydroxyl group –OH). This enables the formation of an intermolecular hydrogen bond of two methanol molecules.

C. Incorrect. Feedback Carbon dioxide, a non-polar species, has no hydrogen atom, therefore it is impossible to form any hydrogen bond. The non-polar molecules typically can’t have hydrogen bonds.

D. Incorrect. Fluoromethane has the electronegative atom F but no hydrogen atom attached to F directly. There is no hydrogen bond between two fluoromethane molecules.

Hydrogen bonds are electrostatic attractions between a hydrogen bearing a partially positive charge and another atom (usually O or N or F) bearing a partially negative charge. It is a strong by the relative positivity of a hydrogen atom attached to an electronegative atom.

CH3OH has the hydroxyl hydrogen connected to the electronegative atom O. The two molecules can form a hydrogen bond as such: CH3O-H …. O(H)-CH3 Solution None of other molecules has the criteria needed to form a hydrogen bond.

The correct answer is (B).

RapidLearningCenter.com  Rapid Learning Inc. All Rights Reserved Question No. 4 of 10 Instructions: (1) Read the problem and answer choices carefully (2) Work the problems on paper as needed (3) Pick the answer (4) Go back to review the core concept tutorial as needed. 4. Boiling point is the temperature at which a liquid boils at a fixed pressure, especially under standard atmospheric conditions. A compound’s boiling point is the point at which ____ and ____ are equal?

(A) Liquid’s vapor pressure & atmospheric pressure. (B) Gas’s vapor pressure & atmospheric pressure. Question (C) Liquid’s vapor pressure & solid’s vapor pressure. (D) Liquid’s vapor pressure & gas’s vapor pressure.

A. Correct! Good job! Boiling occurs when the liquid's vapor pressure equals the atmospheric pressure.

B. Incorrect. Boiling occurs when the liquid's vapor pressure equals the atmospheric pressure.

C. Incorrect. Feedback Boiling occurs when the liquid's vapor pressure equals the atmospheric pressure.

D. Incorrect. Boiling occurs when the liquid's vapor pressure equals the atmospheric pressure.

The boiling point of a substance is the temperature at which the vapor pressure of the liquid equals the pressure surrounding the liquid and the liquid changes into a vapor.

Boiling occurs when the liquid's vapor pressure equals the atmospheric pressure.

The correct answer is (A).

Solution

RapidLearningCenter.com  Rapid Learning Inc. All Rights Reserved Question No. 5 of 10 Instructions: (1) Read the problem and answer choices carefully (2) Work the problems on paper as needed (3) Pick the answer (4) Go back to review the core concept tutorial as needed. 5. Solids can be classified based on their nature of bonding, within and between their molecules. Which of the following statements has a WRONG match in definition?

(A) Metallic solid (Zr)—metal atoms in closest packing with electrons in a large pool. (B) Network solid (Si)—closest packing of non-metal atoms with only physical attractions between atoms. Question (C) (N2O4)—covalent bonding within molecules with only physical attractions between molecules. (D) Ionic Solid (CaCO3)—Closest packing of ions that minimizes like-charged ion repulsions.

A. Incorrect.

Metallic bonding is metal atoms, closest packing, pool of electrons. B. Correct! Great job! Network bonding is non-metals atoms covalently bonded to the neighboring atoms, not non-metal atoms with only physical attractions. C. Incorrect. Molecular solids are covalent bonds within the molecules and physical IMF between Feedback them.

D. Incorrect. Ionic solids are closest packing of ions to minimize like-charge repulsions.

All of the pairings are correct except for the network solid. Network solids are not non-metal atoms with physical attractions. They are non-metals atoms that are covalently bonded to the neighboring atoms.

The correct answer is (B).

Solution

RapidLearningCenter.com  Rapid Learning Inc. All Rights Reserved Question No. 6 of 10 Instructions: (1) Read the problem and answer choices carefully (2) Work the problems on paper as needed (3) Pick the answer (4) Go back to review the core concept tutorial as needed. 6. The enthalpy of fusion or heat of fusion is the change in enthalpy resulting from heating a given quantity of a substance to change its state from a solid to a liquid. The temperature at which this occurs is the melting point. If 825 J are needed to melt a sample of ice, what mass was the sample? The heat of fusion of ice is 334 J/g. The heat of vaporization of ice is 2287 J/g.

(A) 2.47 g Question (B) 0.405 g (C) 0.361 g (D) 2.77 g

A. Correct. Good job! The heat needed to melt is the product of mass and heat of fusion. Convert to the proper units and rearrange the equation to solve the mass. The heat of vaporization is not needed for this calculation.

B. Incorrect.

The heat needed to melt is the product of mass and heat of fusion. Convert to the proper units and rearrange the equation to solve the mass. The heat of vaporization is not needed for this calculation. Check your algebra. C. Incorrect.

Feedback The heat needed to melt is the product of mass and heat of fusion. Convert to the proper units and rearrange the equation to solve the mass. The heat of vaporization is not needed for this calculation. Check your algebra. D. Incorrect. The heat needed to melt is the product of mass and heat of fusion. Convert to the proper units and rearrange the equation to solve the mass. The heat of vaporization is not needed for this calculation. Check your algebra.

H = 825 J

Hfus = 334 J/g m = ? g

For melting, use enthalpy of fusion: The total heat needed H = m x Hfus

-1 Therefore m = H/Hfus = 825 J / 344 Jg = 2.47 g

m = 2.47 g Solution

The correct answer is (A).

RapidLearningCenter.com  Rapid Learning Inc. All Rights Reserved Question No. 7 of 10 Instructions: (1) Read the problem and answer choices carefully (2) Work the problems on paper as needed (3) Pick the answer (4) Go back to review the core concept tutorial as needed. 7. NaCl face-centered cubic lattice, like all lattices, has lattice points at the eight corners of the unit cell plus additional points at the centers of each face of the unit cell. Since the repetition patterns of Na and Cl are the same in the lattice, the Cl sublattice must also be face-centered cubic sublattice. KBr crystalline structure is similar to NaCl lattice, a cubic unit cell. In the face-centered cubic, each corner lattice point counts for 1/8 of an atom, edge ¼, face center ½ and center 1. How many K+ ions and Br- ions are in each unit cell?

Question

(A) 4 K+ ions and 4 Br- ions (B) 12 K+ ions and 12 Br- ions (C) 8 K+ ions and 8 Br- ions (D) 4 K+ ions and 3 Br- ions

(A) Correct! Good job! There are 1/8 K+ at each of 8 corners and ½ K+ at each of 6 face centers. Therefore #K+ = (1/8)x8 + (1/2)x6 = 4. There are ¼ Br- along each of the 12 edges and 1 Br- at the center. Therefore #Br- = (1/4)x12 + 1x1 = 4.

(B) Incorrect. Count the number of atoms at each position and use the face-centered cubic unit cell information provided to add them up for each ion type.

(C) Incorrect. Feedback Count the number of atoms at each position and use the face-centered cubic unit cell information provided to add them up for each ion type.

(D) Incorrect. Count the number of atoms at each position and use the face-centered cubic unit cell information provided to add them up for each ion type.

As the properties of this face-centered cubic, each corner lattice point counts for 1/8 of an atom, edge ¼, face center ½ and center 1. K+: There are 1/8 K+ at each of 8 corners and ½ K+ at each of 6 face centers. Therefore #K+ = (1/8)x8 + (1/2)x6 = 4. Br-: There are ¼ Br- along each of the 12 edges and 1 Br- at the center. #Br- = (1/4)x12 + 1x1 = 4.

Solution The correct answer is (A).

RapidLearningCenter.com  Rapid Learning Inc. All Rights Reserved Question No. 8 of 10 Instructions: (1) Read the problem and answer choices carefully (2) Work the problems on paper as needed (3) Pick the answer (4) Go back to review the core concept tutorial as needed. 8. A phase diagrams illustrates the changes between the states of matter of elements or compounds as they relate to pressure and temperatures. Which statement(s) is (are) true about the phase diagram of water below?

Question

(A) Under 1 atm pressure, water molecules at the surface break intermolecular forces to evaporate at 100C. (B) Line AB represents the water solid-gas equilibrium. (C) At Point B, all three phases of water co-exist. (D) All of the above.

A. Incorrect. Partially correct. The statement is true, water indeed boils at 100C. However, there are more than one statements that are true.

B. Incorrect. Partially correct. The statement is true, line AB is the solid-gas equilibrium. However, there are more than one statements that are true.

C. Incorrect.

Feedback Partially correct. The statement is true. Point B is a triple point. However, there are more than one statements that are true.

D. Correct! Good job! All three statements A, B and C are true. The ice-vapor equilibrium is the line separates the solid from gas. Water boils at 100C and 1atm. The phase diagram depicts the triple point where three phases coexist.

At Point F: It represents the boiling point where molecules break away. Line AB: It is a boundary line between solid and gas phases – at equilibrium. At Point B: Triple points are points on phase diagrams where lines of equilibrium intersect. Triple points mark conditions at which three different phases can coexist. In the water phase diagram, the triple point (B) corresponds to the single temperature and pressure at which solid, liquid, and gaseous water can coexist in a

Solution stable equilibrium.

The correct answer is (D).

RapidLearningCenter.com  Rapid Learning Inc. All Rights Reserved Question No. 9 of 10 Instructions: (1) Read the problem and answer choices carefully (2) Work the problems on paper as needed (3) Pick the answer (4) Go back to review the core concept tutorial as needed. 9. There are four types of intermolecular forces, London Dispersion, Dipole-Dipole, Ionic Forces and Hydrogen Bonding. Most of them depend on the polarity of a

molecule. Which forces are present in CH3F?

(A) London Dispersion Forces. (B) London Dispersion Forces & Dipole-dipole.

Question (C) London Dispersion Forces & Hydrogen-bonding. (D) London Dispersion Forces, Dipole-Dipole and Hydrogen bonding.

A. Incorrect. All molecules have London Dispersion, the weakest intermolecular force of all. This molecule does have London Dispersion Forces, but also another one.

B. Correct! Great job! Fluoromethane, a covalent structure, contains the very electronegative atom F, which makes this molecule polar. All molecules have London Dispersion. This also has Dipole-Dipole. However, since it has no hydrogen attached directly to an electronegative atom such F, this molecule will not have intermolecular hydrogen bonding.

Feedback C. Incorrect. Since it has no hydrogen attached directly to an electronegative atom such F, this molecule will not have intermolecular hydrogen bonding.

D. Incorrect. Since it has no hydrogen attached directly to an electronegative atom such F, this molecule will not have intermolecular hydrogen bonding.

CH3F is a polar molecule. (1) London Dispersion: Every molecule should have this force. (2) Dipole-Dipole: Polar molecules have this stronger force. (3) Hydrogen Bonding: The hydrogen atoms are bonded to the carbon, not ; therefore it cannot have a hydrogen bond. (4) Ionic Force: This is a covalent molecule, not ionic in nature. There is no ionic force in this molecule.

Solution The correct answer is (B).

RapidLearningCenter.com  Rapid Learning Inc. All Rights Reserved Question No. 10 of 10 Instructions: (1) Read the problem and answer choices carefully (2) Work the problems on paper as needed (3) Pick the answer (4) Go back to review the core concept tutorial as needed. 10. Among four types of intermolecular forces, London Dispersion occurs to all molecules, Dipole-Dipole to polar molecules, Ionic Force to ionic compounds and hydrogen bonding to electronegative atom containing structures. Some depend on the size of a molecule. Which intermolecular force is larger for C3H8 than for CH4?

(A) London Dispersion Forces. (B) Dipole-Dipole forces. Question (C) Hydrogen bonding. (D) All forces are the same for these two molecules.

A. Correct! Great job! As size of molecule increases, London Dispersion Forces increases.

B. Incorrect. Both molecules are non-polar. There is no Dipole-Dipole in them.

C. Incorrect.

Feedback There is no hydrogen bonding in either molecule since they do not contain any electronegative atom.

D. Incorrect. There is a difference in the intermolecular forces of these two molecules.

The London dispersion force is the weakest intermolecular force. The London dispersion force is a temporary attractive force that results when the electrons in two adjacent atoms occupy positions that make the atoms form temporary dipoles. This force is sometimes called an induced dipole-induced dipole attraction. London forces are the attractive forces that cause non-polar substances to condense to liquids and to freeze into solids when the temperature is lowered sufficiently.

The larger the molecule, the more electrons there are to gang-up on one side and cause a temporary dipole.

Solution The correct answer is (A).

RapidLearningCenter.com  Rapid Learning Inc. All Rights Reserved