Chapter+3

Chapter 3: Water and the Fitness of the Environment

Answer the following questions in your notebook. You can hand write them or type them.

1. What is electronegativity, and how does it affect interactions between water molecules? Electronegativity is the tendency of an atom to attract electrons in forming and covalent bond. Oxygen is more electronegative than hydrogen, so electrons are attracted to it, making the water molecule unbalanced because of the uneven distribution of electrons. This gives the two sides opposite charges, oxygen being slightly negative and hydrogen being slightly positive. Thus, the positive hydrogen atoms are attracted to the negative charges of oxygen in other molecules, forming a hydrogen bond and making the molecule polar (Bella Fernandez, Christina Egea, Julie Kim)
 * Answer:

2. Water is essential to all living things. Discuss three properties of water.


 * Cohesion is the idea that water molecules have a strong tendency to stick to one another. Water is cohesive because the negative poles are attracted to the positive poles of another molecule through hydrogen bonding and this causes the water molecules to be attracted to stick one another.


 * Adhesion is the water molecule's ability to stick to other substances. For example, in the meniscus of a graduated cylinder, the water molecules stick to the walls of the glass.

(Melanie Catlett, Jillian Nash, and Grace Baumann)
 * Surface tension is the measure of how difficult is to break the surface of a liquid. For example, water bugs are able to walk on water because the surface tension is strong enough to support the weight due to the hydrogen bonding of surface molecules

3. Explain each of the following in terms of properties of water: a. The ability of water to moderate temperature within living organisms and in organisms’ environments. Water moderates air temperature by absorbing heat from air that is warmer and releasing the stored heat to air that is cooler. Because of its high specific heat capacity, water takes longer to warm up and also to cool down, which results in large bodies of water moderating the surrounding land. This means that in winter, the water is warmer than the land and so it will warm it slightly, and in summer the water will be cooler and mooderate the land temperature. (Meghan and Gracie)

b. The movement of water from the roots to the leaves of plants. Adhesion and cohesion are responsible for the movement of water from the roots to the leaves of plants because the water molecules are attracted to the sides of the tubes in the plant, and then the water molecules are attracted to each other, which causes the water to move up the tubes against gravity. (Meghan and Gracie)

4. How can the freezing of water crack boulders? The freezing of water can crack a boulder because when water freezes it expands so if water got into a crack in the boulder, it would expand in the crack causing the boulder to break. (Julia Wolak and Ele Haglund)

5. Compared with a basic solution at pH 8, the same volume of an acidic solution at pH 5 has _ times as many hydrogen ions (H+). An acidic solution at a pH of 5 has 1,000 times as many hydrogen ions as a basic solution at a pH of 8 because when you go from 8 to 7 you gain electrons, as well as when you go to from 7 to 6 and 6 to 5. To go from 8 to 5 you go up 3 numbers on the pH scale and since each increase is x10 you do 10^3 to get the number of hydrogen ions (Julia Wolak and Ele Haglund)

6. What is a buffer? Discuss how carbonic acid functions as a buffer. Buffers are the substances that minimize the changes in concentrations of hydrogen ions and hydroxide ions in solutions. When carbon dioxide reacts with the water found in blood plasma, carbonic acid is formed. The carbonic acid can dissociate to yield bicarbonate and hydrogen ions. The ions balance each other out to add or remove hydrogen ions to stabilize the pH level. (Baily, Julia)