Chapter 11

Carbon and silicon belong to Group 4 A of the periodic table and have the same valence electron configuration \(\left(n s^{2} n p^{2}\right) .\) Why does silicon dioxide \(\left(\mathrm{SiO}_{2}\right)\) have a much higher melting point than carbon dioxide \(\left(\mathrm{CO}_{2}\right) ?\)

A pressure cooker is a sealed container that allows steam to escape when it exceeds a predetermined pressure. How does this device reduce the time needed for cooking?

A \(1.20-\mathrm{g}\) sample of water is injected into an evacuated \(5.00-\mathrm{L}\) flask at \(65^{\circ} \mathrm{C} .\) What percentage of the water will be vapor when the system reaches equilibrium? Assume ideal behavior of water vapor and that the volume of liquid water is negligible. The vapor pressure of water at \(65^{\circ} \mathrm{C}\) is \(187.5 \mathrm{mmHg}\)

What are the advantages of cooking the vegetable broccoli with steam instead of boiling it in water?

Provide an explanation for each of the following phenomena: (a) Solid argon (m.p. \(-189.2^{\circ} \mathrm{C} ;\) b.p. \(-185.7^{\circ} \mathrm{C}\) ) can be prepared by immersing a flask containing argon gas in liquid nitrogen (b.p. \(-195.8^{\circ} \mathrm{C}\) ) until it liquefies and then connecting the flask to a vacuum pump. (b) The melting point of cyclohexane \(\left(\mathrm{C}_{6} \mathrm{H}_{12}\right)\) increases with increasing pressure exerted on the solid cyclohexane. (c) Certain high-altitude clouds contain water droplets at \(-10^{\circ} \mathrm{C}\). (d) When a piece of dry ice is added to a beaker of water, fog forms above the water.

Argon crystallizes in the face-centered cubic arrangement at \(40 \mathrm{~K}\). Given that the atomic radius of argon is \(191 \mathrm{pm}\), calculate the density of solid argon.

A chemistry instructor performed the following mystery demonstration. Just before the students arrived in class, she heated some water to boiling in an Erlenmeyer flask. She then removed the flask from the flame and closed the flask with a rubber stopper. After the class commenced, she held the flask in front of the students and announced that she could make the water boil simply by rubbing an ice cube on the outside walls of the flask. To the amazement of everyone, it worked. Give an explanation for this phenomenon.

Swimming coaches sometimes suggest that a drop of alcohol (ethanol) placed in an ear plugged with water "draws out the water." Explain this action from a molecular point of view.

Use the concept of intermolecular forces to explain why the far end of a walking cane rises when one raises the handle.

Why do citrus growers spray their trees with water to protect them from freezing?

What is the origin of dark spots on the inner glass walls of an old tungsten lightbulb? What is the purpose of filling these lightbulbs with argon gas?

A student heated a beaker of cold water (on a tripod) with a Bunsen burner. When the gas is ignited, she noticed that there was water condensed on the outside of the beaker. Explain what happened.

Sketch the cooling curves of water from about \(110^{\circ} \mathrm{C}\) to about \(-10^{\circ} \mathrm{C}\). How would you also show the formation of supercooled liquid below \(0^{\circ} \mathrm{C}\) which then freezes to ice? The pressure is at 1 atm throughout the process. The curves need not be drawn quantitatively.

Iron crystallizes in a body-centered cubic lattice. The cell length as determined by X-ray diffraction is \(286.7 \mathrm{pm}\). Given that the density of iron is \(7.874 \mathrm{~g} /\) \(\mathrm{cm}^{3},\) calculate Avogadro's number.

The electrical conductance of copper metal decreases with temperature, but that of a \(\mathrm{CuSO}_{4}\) solution increases with temperature. Explain.

Is the vapor pressure of a liquid more sensitive to changes in temperature if \(\Delta H_{\text {vap }}\) is small or large?

Estimate the molar heat of vaporization of a liquid whose vapor pressure doubles when the temperature is raised from \(85^{\circ} \mathrm{C}\) to \(95^{\circ} \mathrm{C}\)