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Chapter 20: Problem 7

In most compounds, the solid phase is denser than the liquid phase. Why isn't this true for water?

Short Answer

Expert verified
In conclusion, the reason why water has a solid phase (ice) with a lower density than its liquid phase is due to the distinct hexagonal lattice structure formed by water molecules when they freeze, which is a direct result of hydrogen bonding between the polar water molecules.

Step by step solution

01

Understand the structure of a water molecule

A water molecule (H2O) has a bent structure with an oxygen atom in the center and two hydrogen atoms bonded to it. The atoms are bonded through covalent bonds, and since oxygen is more electronegative than hydrogen, there's a slight charge difference between them, resulting in a polar molecule.
02

The hydrogen bonding in water

Due to the polar nature of the water molecules, they form hydrogen bonds with neighboring water molecules. An oxygen atom in a water molecule attracts the positively charged hydrogen atoms from the neighboring water molecules, forming the hydrogen bonds. These bonds significantly affect the properties of water, including the density difference between the solid and liquid phases.
03

The structure of water in the liquid phase

In the liquid phase, water molecules are constantly moving and forming and breaking hydrogen bonds with the neighboring water molecules. This constant motion allows the water molecules to be relatively close together, resulting in a higher density.
04

The structure of water in the solid phase (ice)

When water freezes and forms ice, the water molecules slow down and arrange themselves in a hexagonal lattice structure. In this structure, each water molecule forms hydrogen bonds with four neighboring water molecules. As a result, the water molecules are held at a fixed distance from each other, creating open spaces within the hexagonal lattice. This regular arrangement of water molecules with open spaces results in a solid phase with a lower density than the liquid phase.
05

Comparing the density of solid and liquid water

In most substances, the solid phase has a higher density than the liquid phase due to more closely-packed molecules. However, in the case of water, the hydrogen bonds lead to a unique lattice structure in the solid phase, with open spaces that make ice less dense than liquid water. In conclusion, the reason why water has a solid phase (ice) with a lower density than its liquid phase is due to the distinct hexagonal lattice structure formed by water molecules when they freeze, which is a direct result of hydrogen bonding between the polar water molecules.

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Most popular questions from this chapter

Discuss the importance of the \(\mathrm{C}-\mathrm{C}\) and \(\mathrm{Si}-\mathrm{Si}\) bond strengths and of \(\pi\) bonding to the properties of carbon and silicon.

In each of the following pairs of substances, one is stable and known, and the other is unstable. For each pair, choose the stable substance, and explain why the other is unstable. a. \(\mathrm{NF}_{5}\) or \(\mathrm{PF}_{5}\) b. \(\mathrm{AsF}_{5}\) or \(\mathrm{AsI}_{5}\) c. \(\mathrm{NF}_{3}\) or \(\mathrm{NBr}_{3}\)

While selenic acid has the formula \(\mathrm{H}_{2} \mathrm{SeO}_{4}\) and thus is directly related to sulfuric acid, telluric acid is best visualized as \(\mathrm{H}_{6} \mathrm{TeO}_{6}\) or \(\mathrm{Te}(\mathrm{OH})_{6}\) a. What is the oxidation state of tellurium in \(\mathrm{Te}(\mathrm{OH})_{6}\) ? b. Despite its structural differences with sulfuric and selenic acid, telluric acid is a diprotic acid with \(\mathrm{p} K_{\mathrm{a}_{1}}=7.68\) and \(\mathrm{P} K_{a_{2}}=11.29 .\) Telluric acid can be prepared by hydrolysis of tellurium hexafluoride according to the equation $$ \mathrm{TeF}_{6}(g)+6 \mathrm{H}_{2} \mathrm{O}(l) \longrightarrow \mathrm{Te}(\mathrm{OH})_{6}(a q)+6 \mathrm{HF}(a q) $$ Tellurium hexafluoride can be prepared by the reaction of elemental tellurium with fluorine gas: $$ \mathrm{Te}(s)+3 \mathrm{~F}_{2}(g) \longrightarrow \mathrm{TeF}_{6}(g) $$ If a cubic block of tellurium (density \(\left.=6.240 \mathrm{~g} / \mathrm{cm}^{3}\right)\) measuring \(0.545 \mathrm{~cm}\) on edge is allowed to react with \(2.34 \mathrm{~L}\) fluorine gas at \(1.06 \mathrm{~atm}\) and \(25^{\circ} \mathrm{C}\), what is the \(\mathrm{pH}\) of a solution of \(\mathrm{Te}(\mathrm{OH})_{6}\) formed by dissolving the isolated \(\mathrm{TeF}_{6}(g)\) in \(115 \mathrm{~mL}\) solution? Assume \(100 \%\) yield in all reactions.

You travel to a distant, cold planet where the ammonia flows like water. In fact, the inhabitants of this planet use ammonia (an abundant liquid on their planet) much as earthlings use water. Ammonia is also similar to water in that it is amphoteric and undergoes autoionization. The \(K\) value for the autoionization of ammonia is \(1.8 \times 10^{-12}\) at the standard temperature of the planet. What is the \(\mathrm{pH}\) of ammonia at this temperature?

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 \(\mathrm{AlCl}_{3}\) is dissolved in water, it produces an acidic solution. e. Lithium reacts in the presence of excess oxygen gas to form lithium superoxide.
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