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 molecules. 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 molecule with two hydrogen atoms bonded to a highly electronegative atom (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 (gas, 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 gases 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 hydrogen bond 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 intermolecular force 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) Molecular solid (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.