Chemistry 9th Chap 5 : Topic 9 - Maryam Publications

Chemistry Chapter 5 : Topic 9

Electrical Conductivity

1 / 15

A student observes two substances in a lab: Substance A is sodium chloride (NaCl), which forms a crystal lattice of oppositely charged ions, while Substance B is methane (CH₄), which consists of discrete molecules held together by weak intermolecular forces. Based on the nature of bonding and forces of attraction, which conclusion is most appropriate regarding their melting points?

A) Both have equal melting points because molecular size is similar

B) B has a higher melting point because covalent bonds are always stronger than ionic bonds

C) Both A and B have low melting points because all substances expand on heating

D) A has a high melting point due to strong ionic bonds, while B has a low melting point due to weak intermolecular forces

2 / 15

A chemist compares two solids: one is magnesium oxide (MgO), and the other is iodine (I₂). MgO has a giant ionic lattice, whereas iodine exists as simple molecular crystals. Despite both being solids at room temperature, their boiling points differ significantly. What is the main reason for this difference?

A) MgO has strong ionic lattice forces, while iodine is held by weak van der Waals forces.

B) Iodine has ionic bonds while MgO has covalent bonds.

C) MgO has weaker forces than iodine.

D) Both have identical intermolecular forces but different masses.

3 / 15

Consider three substances:

A) NaCl<CO₂< Diamond

B) Diamond < NaCl<CO₂

C) CO₂<NaCl< Diamond

D) CO₂< Diamond <NaCl

4 / 15

A student states: “Covalent compounds always have lower melting points than ionic compounds.” However, graphite (a form of carbon) contradicts this idea partially. Which explanation best justifies this?

A) Graphite is a molecular compound with weak forces overall

B) Graphite has weak ionic bonds between layers

C) Graphite contains metallic bonding

D) Graphite has strong covalent bonds within layers but weak forces between layers

5 / 15

Two compounds X and Y are studied. X has a giant ionic structure, while Y is a simple molecular covalent compound. When heat is applied, Y melts easily but X does not. What is the most logical explanation?

A) X requires breaking strong ionic bonds, while Y only needs weak intermolecular forces to be overcome.

B) X contains weaker intermolecular forces than Y.

C) Y has stronger bonds than X.

D) Both X and Y have identical bonding strength.

6 / 15

Which of the following best explains why sodium chloride has a much higher boiling point than hydrogen chloride (HCl), even though both contain chlorine?

A) Both have identical bonding types but different molecular masses.

B) HCl has stronger bonding due to hydrogen bonding.

C) NaCl contains covalent bonds while HCl contains ionic bonds.

D) NaCl has strong ionic attraction between ions, while HCl has weak intermolecular forces between molecules.

7 / 15

Which statement correctly compares the forces of attraction in ionic and covalent substances?

A) Both have identical forces but different arrangements.

B) Ionic compounds have weak intermolecular forces only.

C) Covalent compounds always have stronger forces than ionic compounds.

D) Ionic compounds have strong electrostatic forces, while covalent molecular compounds have weak intermolecular forces.

8 / 15

A substance melts at a very low temperature and easily evaporates at room temperature. Which structural explanation best fits this observation?

A) It has a giant covalent structure.

B) It contains metallic bonding.

C) It has a giant ionic lattice.

D) It consists of simple molecules with weak intermolecular forces.

9 / 15

Why does diamond have an extremely high melting point compared to wax, even though both are composed of carbon atoms?

A) Wax contains metallic bonding.

B) Wax has ionic bonds while diamond has covalent bonds.

C) Diamond has a giant covalent structure requiring strong bond breaking, while wax has weak intermolecular forces.

D) Both have identical structures but different densities.

10 / 15

Which of the following best describes why ionic compounds are generally solid at room temperature?

A) They contain only covalent bonds.

B) Their molecules are small and light.

C) They contain weak forces that keep particles loosely bound.

D) Strong electrostatic forces hold ions in a rigid lattice structure.

11 / 15

A student ranks substances based on boiling points: CO₂, NaCl, and CaO. Which correct order from lowest to highest boiling point is expected?

A) NaCl<CO₂<CaO

B) CO₂<NaCl<CaO

C) CaO<NaCl<CO₂

D) CO₂<CaO<NaCl

12 / 15

A group of students compares melting points of silicon dioxide (SiO₂) and carbon dioxide (CO₂). They find SiO₂ has a very high melting point while CO₂ is a gas at room temperature. What explains this difference?

A) Both have weak intermolecular forces but different atomic sizes.

B) CO₂ has ionic bonds while SiO₂ has covalent bonds.

C) SiO₂ is molecular and CO₂ is ionic.

D) SiO₂ forms a giant covalent network, while CO₂ is a simple molecular compound.

13 / 15

Why do molecular covalent compounds generally have low melting and boiling points?

A) Because they are always gases.

B) Because covalent bonds are weak.

C) Because they contain no atoms.

D) Because only weak intermolecular forces need to be overcome, not covalent bonds.

14 / 15

Which statement best explains why calcium oxide (CaO) has a higher melting point than sodium chloride (NaCl)?

A) NaCl has covalent bonding.

B) CaO has weaker ionic bonds.

C) CaO has smaller molecules than NaCl.

D) CaO has stronger ionic attraction due to higher charges on ions.

15 / 15

A compound is observed to have a high melting point and conducts electricity when molten. What type of bonding is most likely present?

A) Hydrogen bonding

B) Giant covalent bonding

C) Ionic bonding

D) Simple covalent bonding

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