Which of the following statement(s) is(are) true? a. The...

Which of the following statement(s) is(are) true? a. The alkali metals are found in the earth’s crust in the form of pure elements. b. Gallium has one of the highest melting points known for metals. c. When calcium metal reacts with water, one of the products is $\mathrm{H}_{2}(g) .$ d. When AlCl $_{3}$ is dissolved in water, it produces an acidic solution. e. Lithium reacts in the presence of excess oxygen gas to form lithium superoxide.

Which of the following statement(s) is(are) true?
a. The alkali metals are found in the earth’s crust in the form of pure elements.
b. Gallium has one of the highest melting points known for metals.
c. When calcium metal reacts with water, one of the products is $\mathrm{H}_{2}(g) .$
d. When AlCl $_{3}$ is dissolved in water, it produces an acidic solution.
e. Lithium reacts in the presence of excess oxygen gas to form lithium superoxide.

Key Concepts

Hydrolysis of Metal Halides

When certain metal halides dissolve in water, they undergo hydrolysis to produce acidic solutions. This occurs because the metal ions, often acting as Lewis acids, interact with water molecules, leading to the formation of acidic species. The extent and nature of the acidic solution depend on the specific metal ion's properties and its hydrolysis reaction with water.

Formation of Metal Oxidation Products

Metals react with oxygen to form various types of oxides, peroxides, and superoxides, depending on factors like the metal's size and electron configuration. Light alkali metals typically form oxides or peroxides rather than superoxides because their small ionic radii do not stabilize the superoxide ion effectively, highlighting the importance of periodic trends in determining the product of oxidation reactions.

Reactivity of Alkaline Earth Metals with Water

Metals in the alkaline earth group, such as calcium, react with water to produce hydroxides and liberate hydrogen gas. The reactivity of these metals with water is a reflection of their inherent tendency to lose electrons, which facilitates the formation of ionic compounds and the evolution of gaseous hydrogen during the reaction.

Melting Point Trends in Metals

The melting point of a metal is largely influenced by the strength of the metallic bonds, atomic size, and crystal structure. While some metals have high melting points due to strong bonds and densely packed structures, others, like gallium, are unusual; gallium has a low melting point, making it one of the few metals that are liquid near room temperature.

Reactivity of Alkali Metals

Alkali metals are highly reactive elements that do not occur in nature in their pure, elemental form due to their strong tendency to form compounds. Instead, they are commonly found in mineral salts in the earth’s crust, as their reactivity leads them to readily combine with other elements such as halogens or oxygen.

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