AP Chemistry Unit 3 Review

Which of the following explains how the dispersion-force model of intermolecular attraction does not account for the unusually high boiling point of HF?

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

• The F2 molecule has a greater mass than the HF

  HF molecule has.

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

• 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.

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?

• 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.

This form of boron nitride is one of the hardest substances known. Which of the following best helps explain why boron nitride is so hard?

• Boron ions and nitrogen ions are held together by ionic bonds.

• Boron nitride is a network solid of atoms connected by covalent bonds with fixed bond angles.

• Boron nitride is an alloy, and alloys are typically harder than the elements used to make them.

• Boron nitride is a polymer made of long chains of boron atoms and nitrogen atoms held together by dispersion forces.

Compounds NaCl MgS, which statement correctly identifies diagram 1 and identifies the compound with the lower melting point.

• Diagram 1 represents MgS; it has a lower melting point than NaCl because the coulombic attractions between its doubly charged Mg 2+ ions and the S 2− ions are stronger than those between the ions in NaCl.

• 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

  NaCl are stronger than those between the ions in MgS.

• 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.

Tags

NGSS.HS-PS1-3

Which statement best helps to explain the observation that NH3(l) boils at −28°C, whereas PH3(l) boils at −126°C?

• The dispersion forces in NH3 are weaker than the dispersion forces in PH3.

• The dispersion forces in NH3 are stronger than the dipole-dipole forces in PH3.

• NH3 has hydrogen bonding that is stronger than the dipole-dipole forces in PH3.

Of the following, the best explanation for the fact that most gases are easily compressed is that the molecules in a gas

• are in constant motion

• are relatively far apart

• have relatively small masses

• have a real, nonzero volume

Tags

NGSS.HS-PS2-1

A gas mixture at 0°C and 1.0atm contains 0.010mol

0.010mol of H2, 0.015mol of O2, and 0.025mol

0.025mol of N2. Assuming ideal behavior, what is the partial pressure of hydrogen gas (H2) in the mixture?

• About 0.20atm 0.20atm, because H2 comprises 20%

  20% of the total number of moles of gas.

• About 0.050atm, because there is 0.050mol of gases at 0°C and 1.0atm.

• About 0.010atm, because there is 0.010mol

  0.010mol of H2 in the sample.

A 2 L container will hold about 4 g of which of the following gases at 0°C and 1 atm?

• SO₂

• N₂

• CO₂

• C₄H₈

A sample of an ideal gas is cooled from 50.0oC to 25.0oC in a sealed container of constant volume. Which of the following values for the gas will decrease?

I. The average molecular mass of the gas

II. The average distance between the molecules

III. The average speed of the molecules

• only I

• only II

• only III

• I and III

Tags

NGSS.HS-PS2-1

A student uses visible spectrophotometry to determine the concentration of CoCl2(aq) in a sample solution. First the student prepares a set of CoCl2(aq) solutions of known concentration. Then the student uses a spectrophotometer to determine the absorbance of each of the standard solutions at a wavelength of 510nm and constructs a standard curve. Finally, the student determines the absorbance of the sample of unknown concentration.

The original solution used to make the solutions for the standard curve was prepared by dissolving 2.60g of

CoCl2 (molar mass 130.g/mol) in enough water to make 100.mL of solution. What is the molar concentration of the solution?

• .200 M

• .500 M

• 1.00 M

• 5.00 M