Ap Chem Unit 3 Review

1. The diagram opposite is a molecular model of a gaseous

  diatomic element that is just above its boiling point.

Intermolecular forces between the gas molecules will cause

them to condense into the liquid phase if the temperature is lowered.

Which of the following best describes how the model is limited in its depiction of the phenomenon?

• 1. It does not show how hydrogen bonds are constantly forming, breaking, and reforming, which results in a net force of attraction between the molecules.

• It does not show how the interactions between ions and the induced molecular dipoles result in a net force of attraction between the molecules.

• It does not show how the interacting permanent dipoles of the molecules result in a net force of attraction between the molecules.

• It does not show how the temporary fluctuating dipoles of the molecular electron clouds result in a net force of attraction between the molecules.

Tags

NGSS.HS-PS1-3

The electron cloud of HF is smaller than that of F2 , however, HF has a much higher boiling point than has F2 . Which of the following explains how the dispersion-force model of intermolecular attraction does not account for the unusually high boiling point of HF ?

• 1. F2 is soluble in water, whereas HF is insoluble in water.

• 1. The F2 molecule has a greater mass than the HF molecule has.

• Liquid F2 has weak dispersion force attractions between its molecules, whereas l iquid HF has strong ionic interactions between H+ and F- ions.

• 1. Liquid F2 has weak dispersion force attractions between its molecules, whereas liquid HF has both weak dispersion force attractions and hydrogen bonding interactions between its molecules.

Four different liquid compounds in flasks at are represented above. The table below identifies the compounds. Flask C shows the most particles in the vapor phase.

Which of the following is not shown in the model but best helps to explain why flask C must contain pentane?

• 1. The random motion of the particles within the liquids.

• The relative speeds of the vapor particles in each flask.

• The strength of the intermolecular forces between the particles in the liquids.

• 1. The structural formula of the molecules of the liquid and vapor in each flask.

Tags

NGSS.HS-PS3-4

1. The structural formula of the molecules of the liquid and vapor in each flask.

• a

• b

• c

• d

4. In which of the following liquids do the intermolecular forces include dipole-dipole forces?

• F2 (l)

• CH4 (l)

• CF4 (l)

• CH2F2 (l)

4. The London (dispersion) forces are weakest for which of the following gases under the same conditions of temperature and pressure?

• A H2

• B O2

• C Xe

• D F2

• E N2

4. Thymine and adenine form a base pair in the DNA molecule. These two bases can form a connection between two strands of DNA via two hydrogen bonds.

Which of the following diagrams shows the correct representation of the hydrogen bonding (denoted by dashed lines) between thymine and adenine base pairs?

(In each diagram, thymine is shown at the left and adenine is shown at the right. The bases are attached to the backbone portion of the DNA strands.)

• a

• b

• c

• d

Which of the following is the strongest type of interaction that occurs between the atoms within the circled areas of the two molecules represented below?

• polar covalent bond

• non-polar covalent bond

• hydrogen bond

• london dispersion force

The ionic compounds NaCl and MgS are represented by the diagrams above. Which statement correctly identifies diagram 1 and identifies the compound with the lower melting point, explaining why?

• Diagram 1 represents NaCl ; it has a lower melting point than MgS has because the coulombic attractions between the singly charged Na+ ions and the Cl- ions in NaCl are stronger than those between the ions in MgS

• 1. Diagram 1 represents NaCl ; it has a lower melting point than MgS because the coulombic attractions between its singly charged Na+ ions and the Cl- ions are weaker than those between the ions in MgS.

• 1. Diagram 1 represents MgS ; it has a lower melting point than NaCl because the coulombic attractions between its doubly charged Mg2+ ions and the S2- ions are stronger than those between the ions in NaCl.

• 1. Diagram 1 represents MgS ; it has a lower melting point than NaCl because the coulombic attractions between the doubly charged Mg2+ ions and the S2_ ions are weaker than those between the ions in NaCl.

Tags

NGSS.HS-PS1-3

NGSS.HS-PS2-4

2. A sample of a hard, solid binary compound at room temperature did not conduct electricity as a pure solid but became highly conductive when dissolved in water.

Which of the following types of interactions is most likely found between the particles in the substance?

• A ionic bonds

• B

  metallic bonds

• C covalent bonds

• D

  hydrogen bonds

Tags

NGSS.HS-PS1-3