Water and Life

1. Chapter 3 Water and Life Questions prepared by Ruth BuskirkUniversity of Texas at Austin Jung ChoiGeorgia Institute of Technology

2. The four emergent properties of water that are important for life are: • Cohesion, expansion upon freezing, high heat of evaporation, and capillarity • Cohesion, moderation of temperature, expansion upon freezing, and solvent properties • Moderation of temperature, solvent properties, high surface tension, and capillarity • Heat of vaporization, high specific heat, high surface tension, and capillarity • Polarity, hydrogen bonding, high specific heat, and high surface tension

3. Which one of the following hypothetical changes in a water molecule would tend to make it more polar? • It is a linear molecule, as in H-O-H. • Adjacent water molecules form covalent bonds with each other. • The electronegativity values for H is increased. • The electronegativity value for O is increased. • All of the above would make water more polar.

4. Water has an unusually high specific heat. This is directly related to which one of the following? • At its boiling point, water changes from liquid to vapor. • More heat is required to raise the temperature of water. • Ice floats in liquid water. • Salt water freezes at a lower temperature than pure water. • Floating ice can insulate bodies of water.

5. Which of the following explains what is happening when sodium chloride dissolves in water? • More hydrogen bonds are forming between water molecules. • Sodium and chloride atoms are separating from one another. • Hydration shells are forming around the sodium and chloride ions. • Covalent bonds are breaking and re-forming. • Nonpolar substances are mixing with polar substances.

6. Surfactants reduce surface tension of a liquid. Which of the following would result if water was treated with surfactants? • Surfactant-treated water droplets will form a thin film instead of beading on a waxed surface. • Surfactant-treated water will form smaller droplets when dripping from a sink. • Water striders will sink. • All of the above will occur • Only a and c will occur.

7. Predict how life on earth would be different if water were less polar. Which one of the following would result if organisms lived in and consisted of a less polar medium than water? • Heavier insects than water striders would be able to walk on the surface of a pond. • Increased cohesion would contribute to increased upward water transport in plants. • The water temperature of ponds and pools would increase more slowly when in sunlight. • Sweating would be a less effective means of keeping cool. • More salts would go into the solution in blood and body fluids.

8. In a lake, mineral nutrients accumulate at the bottom while dissolved oxygen is greater near the surface. These nutrients can be mixed during water turnover that occurs with annual temperature changes. Which one of the following properties of water explains this turnover? • Individual water molecules move less vigorously as water cools. • Hydrogen bonds among water molecules form a crystal lattice at 0°C. • The density of water is greatest at 4°C. • Water changes from liquid to solid at 0°C. • The distance between water molecules is greater in ice than in liquid form.

9. A calorie is defined as: • The amount of energy required to raise the temperature of 1 gram of water by 1 degree F. • The amount of energy required to raise the temperature of 1 gram of water by 1 degree C. • The amount of energy released by metabolism of one gram of glucose. • The amount of energy contained in one gram of fat. • The amount of energy required to raise the temperature of 1 liter of water by 1 degree C.

10. To make a 1 M solution of calcium chloride (CaCl2), you would place how many gm of CaCl2 into a container and then add how much pure water?[mass of a Ca atom = 40; mass of a Cl atom = 35; mass of an O atom = 16; mass of an H atom = 1] • 75 gm of CaCl2 then add 1 liter of water • 110 gm of CaCl2 then add 1 liter of water • 128 gm of CaCl2 then add 1 liter of water • 75 gm of CaCl2 then add water to make a total volume of 1 liter • 110 gm of CaCl2 then add water to make a total volume of 1 liter

11. In humans, blood pH is around 7.4, and a decrease in blood pH to 6.4 would be fatal. A drop by 1 pH unit represents which of these? • 1/10 as many H+ ions in the solution • 1/7 as many H+ ions in the solution • 1/2 as many H+ ions in the solution • twice as many H+ ions in the solution • ten times as many H+ ions in the solution

12. The chemical equilibrium between carbonic acid and bicarbonate acts as a pH regulator in our blood. If the blood pH begins to rise, what will happen?H2CO3 ↔ HCO3– + H+ Carbonic acid Bicarbonate ion Hydrogen ion • reaction proceeds to the right; more carbonic acid dissociates • reaction proceeds to the right; more carbonic acid forms • reaction proceeds to the left; more carbonic acid dissociates • reaction proceeds to the left; more carbonic acid forms

13. Scientists are concerned about increased concentrations of atmospheric carbon dioxide due to increased fossil fuel combustion and deforestation. In addition to major effects on global temperatures, increased levels of CO2 can threaten aquatic organisms in which way? • forming more carbonic acid in a solution that raises the pH of seawater • forming more carbonic acid that decreases the concentration of carbonate ions in seawater • increasing photosynthesis rates in aquatic plants and algae • decreasing the oxygen available for cellular respiration in aquatic organisms • increasing the levels of harmful sulfur oxides and nitrous oxides