AP Chemistry: 3.2 Properties of Solids – Exam Style questions with Answer- MCQ

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Question

The diagrams above represent two allotropes of solid phosphorus. Which of the following correctly identifies the allotrope with the higher melting point and explains why?
A Allotrope I , because it has \(P_4\) molecules with covalent bonds that are stronger than dispersion forces between individual P atoms in allotrope II.
B Allotrope II , because it has covalent bonds between the phosphorous atoms that are stronger than the dispersion forces between the \(P_4\) molecules in allotrope I.
C Allotrope II , because it has metallic bonding that is stronger than the covalent bonding found in the \(P_4\) molecules in allotrope I
D Both allotropes have the same melting point because they both contain phosphorous atoms.
▶️Answer/Explanation

Ans:B

Allotrope II has a high melting point because its atoms are covalently bonded in a network solid. The covalent bonds are stronger than the dispersion forces between \(P_4\) molecules in allotrope I.

Question

 

The crystal structure of NaBr is represented in the diagram above. Which statement correctly compares crystalline NaBr(s) to molten NaBr(l) in terms of electrical conductivity?

A Crystalline NaBr contains no freely moving electrons that could conduct an electrical current, whereas electrons can flow freely in molten NaBr , which is a good conductor of electricity.
B Crystalline NaBr and molten NaBr both contain ions that are held in fixed positions due to strong electrostatic attractions among the ions, making neither a good electrical conductor.
C Crystalline NaBr and molten NaBr both contain Na atoms that transfer electrons to Br atoms in a chemical reaction, thus allowing them both to be good conductors of electricity.
D  Crystalline NaBr contains no freely moving electrons to conduct electricity, but molten NaBr is composed of freely moving Na+ and Br− ions, which allows it to be a good conductor of electricity.
▶️Answer/Explanation

Ans: D

In crystalline NaBr , there are no free electrons (or any other charged particles) that can move to carry an electrical current. But when molten, NaBr has freely moving ions that can carry an electric current.

Question

 

The structures of two allotropes of carbon are represented above. Which of the following statements best helps explain why diamond is much harder than graphite?

A  Diamond contains covalent bonds, whereas graphite contains ionic bonds.
B  Diamond contains ionic bonds, whereas graphite contains covalent bonds.
C  Carbon atoms in diamond have four covalent bonds, whereas graphite is made of layers that are held together by relatively weak dispersion forces.
D  Carbon atoms in diamond have a sea of mobile electrons that make the structure strong, whereas graphite does not contain delocalized electrons.
▶️Answer/Explanation

Ans: C

Diamond is a covalent network solid with each carbon atom bonded to four other carbon atoms. Graphite has a layered structure with each carbon atom bonded to three other carbon atoms. Dispersion forces hold the layers together, but the forces are relatively weak, and the layers can slide past each other.

Question

Which of the following could be the identity of a white crystalline solid that exhibits the following properties?

  •  It melts at \(320^{\circ}\) C.
  •  It does not conduct eletricity as a solid.
  •  It conducts eletricity in an aqueous solution.

(A)\(C_{6}H_{12}O_{6}^{S}\)

(B) NaOH(s)

(C) \(SiO_{2}\)

(D)Cu(s)

▶️Answer/Explanation

Ans:B

Question

At room temperature \(I_2\)(s) is a molecular solid. Which of the following provides a characteristic of \(I_2\)(s) with a correct explanation?
(A) It has a high melting point because it has weak intermolecular forces.

(B) It is hard because it forms a three- dimensional covalent network.

(C) It is not a good conductor of electricity because its valence electrons are localized in bonding and nonbonding pairs.

(D) It is very soluble in water because its molecules are polar.

▶️Answer/Explanation

Ans:B

Question.

Based on the diagram above, which of the following best helps to explain why MgO(s) is not able to conduct electricity, but MgO(s) is a good conductor of electricity?

(A) MgO(s) does not contain free electrons, but MgO(I) contains free electrons that can flow.

(B) MgO(s) contains no water, but MgO(l) contains water that can conduct electricity.

(C) MgO(s) consists of separate\( Mg^{2+} \)ions and \(O^{2-} \)ions, but Mg(O) contains MgO molecules that can conduct electricity.

(D) MgO(s) consists of separate\( Mg^{2+} \)ions and\( O^{2-} \)ions held in a fixed lattice, but in Mg(O) the ions are free to move and conduct electricity.

▶️Answer/Explanation

Ans:C

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