Review Questions for Chapter 2 - The Chemical Foundation of Life

The unique properties of water are important in biological processes. For the following 3 properties of water (cohesion, adhesion & high heat vaporization), define the property and give one example of how the property affects living organisms.

1. Cohesion is the attraction between the water molecules which helps create surface tension. Insects can walk on water because of cohesion. 2. Adhesion is the attraction between water molecules and other molecules. Water moving up from the roots of plants to the leaves as a result of capillary action because of adhesion. 3. Heat of vaporization is the amount of energy required to convert liquid into gas. This property helps humans maintain homeostasis of body temperature by evaporation.

4 true statements about bonds.

1. Electrons are unequally shared in polar covalent bonds. 2. Electrons are equally shared in nonpolar covalent bonds. 3. Hydrogen bonds are weak bonds based on electrostatic forces. 4. Ionic bonds are not generally stronger than covalent bonds.

What are 3 examples of how the characteristics of water are important in maintaining life?

1. The lower density of water as a solid vs a liquid allows ice to float which forms an insulating surface layer for aquatic life. 2. The high specific heat capacity of water insulates aquatic life or bodily fluids from temperature changes. 3. The high heat of vaporization of water allows animals to cool themselves by sweating.

4 true statements about water.

1. Water is polar. 2. Water can stabilize the temperature of nearby air. 3. Water is essential for life. 4. Water is NOT the most abundant molecule in the Earth's atmosphere.

What is the maximum number of atoms or molecules a single carbon atom can bond with?

4 because the carbon atom has 4 electrons in its valence shell. Therefore, bonding 4 more electrons will complete its octet, allowing it to attain a stable configuration. A carbon molecule can therefore bond with a maximum of 4 other atoms.

If xenon has an atomic number of 54 and a mass number of 108, how many neutrons does it have?

54

Which of the following statements is true about acids and bases?

Acids and bases can neutralize each other. Acids add H^+ ions in a solution, while bases add OH^- ions to a solution. These ions neutralize each other by forming water molecules.

In a solution, what kind of molecule binds up excess hydrogen ions?

Bases bind excess H+ ions in solution, resulting in a neutral solution. For example, the addition of OH- to H+ produces water.

Discuss how buffers help prevent drastic swings in pH.

Buffers absorb excess hydrogen and hydroxide ions (produced by chemical reactions) to prevent increases of decreases in pH since they can bond to these ions. An example is the bicarbonate system in the human body. This system is able to absorb hydrogen and hydroxide ions to prevent changes in pH and keep cells functioning properly.

What property of carbon makes it essential for organic life?

Carbon is found in all living things because it can form up to four covalent bonds. These strong covalent bonds allow the formation of long chains that combine to form proteins and DNA.

Looking at the figure, can you infer which two groups together will form a strong ionic bond?

Group 1 and Group 17 will form a strong ionic bond. Group 1 has one valence electron, so to obtain a stable configuration, it will donate the electron readily. Group 17 has 7 electrons in its valence shell. In order to obtain a stable configuration, it will accept one electron readily.

Which type of bond exemplifies a weak chemical bond?

Hydrogen bond because a hydrogen bond forms between hydrogen and an electronegative atom. It is weak because electrons are not shared as they are in a covalent bond nor are they transferred to form opposite, attracting charges, as they are in ionic bonds. Instead hydrogen has a slight positive charge when covalently bonded to a more electronegative atom, because that atom draws the hydrogen's electron away from it, causing it to become attracted to nearby electronegative atoms with unpaired electrons.

Why are hydrogen bonds and van der Waals interactions necessary for cells?

Hydrogen bonds and van der Waals interactions form weak associations between and/or within molecules, providing the necessary shape and structure of DNA and proteins to function in the body.

Based on the information provided, which of the following statements is false?

In HCL(aq) the hydrogen atom acquires a partial positive charge, and the chlorine atom acquires a partial negative charge.

Why can some insects walk on water?

Insects can walk on water because of its high surface tension.

What forms ionic bonds?

Ions with opposite charges.

What are atoms that vary in the number of neutrons found in their nuclei called?

Isotopes. These are atoms that have the sam number of protons, but differ in the number of neutrons.

Which of the following functional groups is not polar?

Methyl groups are nonpolar because carbon and hydrogen have similar electronegativity. this means the covalent bond between carbon and hydrogen has electrons that are equally shared by the carbon and hydrogen. Therefore, it is a nonpolar molecule.

What are enantiomers?

Molecule that share the same chemical bonds are mirror images of each other.

Compare and contrast saturated and unsaturated triglycerides.

Saturated triglycerides contain no double bonds between carbon atoms; they are usually solid at room temperature. Unsaturated triglycerides contain at least one double bond between carbon atoms; they are usually liquid at room temperature.

Potassium has an atomic number of 19. What is its electron configuration?

Shells 1, 2, and 3 are full, as they hold a total of 18 electrons, and shell 4 has the remaining one electron and is unfilled.

Which of the following is NOT a functional group that bond with carbon?

Sodium because it is not a functional group, it is an element. Thus, it does not bond with carbon as a functional group.

Why can water be a good insulator within the body of endothermic (warm-blooded) animals?

Specific heat capacity because specific heat is defined as the amount of heat one gram of a substance must absorb or lose to change its temperature by 1 degree Celsius. Therefore, warm-blooded animals use water to more evenly disperse hear in their bodies. It takes a large amount of energy to hear or cool water.

Define water's property of adhesion.

The attraction between water molecules and other molecules. Adhesion is the tendency of different particles to cling to one another. It is sometimes a strong adhesive force, such as when water is exposed to charged surfaces.

What property of carboxyl makes carboxyl containing molecules hydrophilic? Which macromolecules contain carboxyl?

The carboxyl group is found in amino acids, some amino acid side chains, and the fatty acids that form triglycerides and phospholipids. This carboxyl group ionizes to release hydrogen ions (H^+) from the group, resulting in the negatively charges group, which contributes to the hydrophilic nature of whatever molecule it is found on.

List the mass number and atomic number of carbon-12 and carbon-13 respectively.

The mass number and atomic number of carbon-13 is 13 and 6, while that of carbon-12 is 12 and 6, respectively.

Why do hydrogen and oxygen form polar covalent bonds within water molecules?

The oxygen atom nucleus is more attractive to the electrons of a hydrogen atom than the hydrogen nucleus is to the oxygen's electrons. Therefore, the hydrogen atom acquires a partial positive charge while the oxygen atom acquires a partial negative charge.

What happens to the pH of a solution when acids are added?

The pH of the solution decreases. An acid is a substance that increases the H+ ion concentration of the solution by dissociating its H+ atoms. Thus, the pH of the solution decreases on addition of a hydrogen atom.

Describe the pH scale and how it relates to living systems. Give an example of how drastic pH changes are prevented in living systems.

The pH scale ranges from 0 to 14, where anything below 7 is acidic and above 7 is alkaline. The bicarbonate system in the human body buffers the blood.

Which of the following statements is true about enantiomers?

To be enantiomers, a molecule must have at least 4 different atoms or groups connected to a central carbon.