Question
Which of the following diagrams best illustrates how a displacement in an ionic crystal results in cleavage and brittleness?
Answer/Explanation
Ans:A
Crystals of native metals (e.g. copper) can be treated as an array of positive ions surrounded by a “gas” of free electrons. When a metallic crystal is subject to forces that displace one plane of atoms with respect to another, the environment of the charged species is left unchanged: there are still “free” electrons between the positive cations, regardless of their changed positions. As a result, metals are malleable: their atomic planes tend to slip without breaking the crystal.
Question
Which of the following diagrams best illustrates how a displacement in an ionic crystal results in cleavage and brittleness?
Answer/Explanation
Ans:A
Crystals of native metals (e.g. copper) can be treated as an array of positive ions surrounded by a “gas” of free electrons. When a metallic crystal is subject to forces that displace one plane of atoms with respect to another, the environment of the charged species is left unchanged: there are still “free” electrons between the positive cations, regardless of their changed positions. As a result, metals are malleable: their atomic planes tend to slip without breaking the crystal.
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
A white crystalline solid that melts at \(320^{\circ} \text{C}\), does not conduct electricity as a solid, but conducts in an aqueous solution suggests an ionic compound that dissociates in water to form ions. Among the options, \(\mathrm{NaOH}(s)\) fits the description. It melts at approximately \(320^{\circ} \text{C}\), does not conduct electricity as a solid (indicating it’s not a metal), and conducts electricity in an aqueous solution because it dissociates into \(\mathrm{Na}^+\) and \(\mathrm{OH}^-\) ions. Thus, the answer is (B).
Question
Which of the following is the best piece of laboratory glassware for preparing \(500.0 \mathrm{~mL}\) of an aqueous solution of a solid?
(A) Volumetric flask
(B) Erlenmeyer flask
(C) Test tube
(D) Graduated beaker
(E) Graduated cylinder
▶️Answer/Explanation
Ans:A
(A) Volumetric flask – Correct. A volumetric flask is the best choice for accurately preparing a specific volume of solution.
(B) Erlenmeyer flask – Not the best choice for accurately measuring volume.
(C) Test tube – Too small for preparing 500 mL of solution.
(D) Graduated beaker – Can be used, but not as accurate as a volumetric flask.
(E) Graduated cylinder – Can be used, but not as accurate as a volumetric flask.
The correct answer is (A) Volumetric flask.