Chapter 2

Create a concept map to organize your understanding of the life-supporting properties of water. A sample map is in the answer section, but the value of this exercise is in the thinking and integrating you must do to create your own map.

Changing the ______ would change it into an atom of a different element. a. number of electrons surrounding the nucleus of an atom b. number of protons in the nucleus of an atom c. electrical charge of an atom d. number of neutrons in the nucleus of an atom

A solution at \(\mathrm{pH} 6\) contains _____ \(\mathrm{H}^{+}\) than the same amount of a solution at \(\mathrm{pH} 8\). a. 20 times more b. 100 times more c. 2 times less d. 100 times less

Most of the unique properties of water result from the fact that water molecules a. are the most abundant molecules on Earth's surface. b. are held together by covalent bonds. c. are constantly in motion. d. are polar and form hydrogen bonds.

A can of cola consists mostly of sugar dissolved in water, with some carbon dioxide gas that makes it fizzy and makes the pH less than \(7 .\) In chemical terms, you could say that cola is an aqueous solution where water is the _____, sugar is a _____, and carbon dioxide makes the solution _____. a. solvent ... solute ... basic b. solute ... solvent ... basic c. solvent ... solute ... acidic d. solute ... solvent ... acidic

The atomic number of sulfur (S) is 16. Sulfur combines with hydrogen by covalent bonding to form a compound, hydrogen sulfide. Based on the number of valence electrons in a sulfur atom, predict the molecular formula of the compound. (Explain your answer.) a. \(\mathrm{HS}\) b. \(\mathrm{H}_{2} \mathrm{~S}\) c. \(\mathrm{H}_{4} \mathrm{~S}_{2}\) d. \(\mathrm{H}_{4} \mathrm{~S}\)

In terms of electron sharing between atoms, compare nonpolar covalent bonds, polar covalent bonds, and ions.

What do you think the effect on the properties of water would be if oxygen and hydrogen had equal electronegativity?

A recent experimental study looked at the combined effects of ocean acidification (see Module 2.15\()\) and increased ocean temperatures, both aspects of climate change, on the growth of polyps, juvenile coral animals. Researchers reported the average polyp biomass (in \(\mu \mathrm{g} /\) polyp) after 42 days of growth under four treatments: a control with \(\mathrm{pH}\) and temperature maintained close to normal reef conditions, a pH lowered by 0.2 units, a temperature raised by \(1^{\circ} \mathrm{C},\) and a combined lower \(\mathrm{pH}\) and higher temperature. The results showed that polyp biomass was reduced somewhat in both the low-pH and high-temperature treatments, but the combined treatment resulted in a reduction in growth by almost a third-a statistically significant result. Experiments often look at the effects of changing one variable at a time, while keeping all other variables constant. Explain why this experiment considered two variables-both a higher temperature and a lower \(\mathrm{pH}\) -at the same time.

In agricultural areas, farmers pay close attention to the weather forecast. Right before a predicted overnight freeze, farmers spray water on crops to protect the plants. Use the properties of water to explain how this method works. Be sure to mention why hydrogen bonds are responsible for this phenomenon.

This chapter explains how the emergent properties of water contribute to the suitability of the environment for life. Until fairly recently, scientists assumed that other physical requirements for life included a moderate range of temperature, \(\mathrm{pH}\), and atmospheric pressure. That view has changed with the discovery of organisms known as extremophiles, which have been found flourishing in hot, acidic sulfur springs and around hydrothermal vents deep in the ocean. What does the existence of life in such environments say about the possibility of life on other planets?