Chapter 3 - Water And Life + Test Review Flashcards
What is electronegativity, and how does it affect interactions between water molecules?
Electronegativity is the attraction of an atom for the electrons of a covalent bond. Because oxygen (3.5) is more electronegative than hydrogen (2.1) the oxygen atom in H2O pulls electrons towards itself, resulting in a partial negative charge on the oxygen atom and partial positive charges on the hydrogen atoms. Atoms in neighboring water molecules with opposite partial charges are attracted to each other, forming a hydrogen bond.
Why is it unlikely that two neighboring water molecules would be arranged like this?
H H / \ O O \ / H H
The hydrogen atoms of one molecule, with their partial positive charges, would repel the hydrogen atoms of the adjacent molecule.
What would be the affect on the properties of the water molecule if oxygen and hydrogen had equal electronegativity?
The covalent bonds of water molecules would not be polar, and the water molecules would not form hydrogen bonds with each other.
What is a polar covalent bond?
A bond in which electrons are shared unequally. The shared electrons are pulled closer to the more electronegative atom making it slightly negative and the other atoms more positive.
What is a polar molecule?
A molecule with an uneven distribution of charges in different regions of the molecule. Example - H2O - O has a partial negative charge and H a partial positive charge.
What is a hydrogen bond?
Oppositely charged regions of neighboring water molecules are attracted to each other. The electrons spend more time near O than H.
Describe how properties of water contribute to the upward movement of water in a tree.
Hydrogen bonds hold neighboring water molecules together. This cohesion helps chains of water molecules move upward against gravity in water conducting cells as water evaporates from the leaves. Adhesion between water molecules and the walls of the water conducting cells also helps counter gravity.
What are the four properties of water?
1) Cohesion
2) Temperature stabilizing capacity
3) Insulation of bodies of water by ice (Expansion upon freezing)
4) Solvent properties
Explain cohesion.
The linking together of like molecules, often by hydrogen bonds (which hold water molecules together). Also helps the transport of water and other dissolved nutrients against gravity in plants.
What is adhesion?
The clinging of one substance to another. An attraction between different substances. Example - water and plant cell walls.
What is surface tension?
A measure of how difficult it is to stretch or break the surface of a liquid. (Due to hydrogen bonding, water has a high surface tension)
Explain how water moderates air temperature.
Water moderates air temperature by absorbing heat from air that is warmer and releasing stored heat to air that is cooler (with only a slight change to its own temperature).
What is kinetic energy?
The energy of motion.
What is thermal energy?
The kinetic energy associated with random motion of atoms or molecules.
What is temperature?
A measure of energy that represents the average kinetic energy of the molecules in a body of matter.
Define heat.
Thermal energy in transfer from one body of matter to another.
What is a calorie?
The amount of heat required to raise the temperature of 1g of water by 1 degree C. And also the converse.
What is a kilocalorie?
1,000 calories. The quantity of heat required to raise the temperature of 1 kg of water by 1 degree C.
Define specific heat.
The amount of heat that must be absorbed or lost for 1 g of that substance to change its temperature by 1 degree C.
What is the specific heat of water? Explain it’s importance.
1 calorie / g / degree C
- Water has a high specific heat and resists changing its temperature due to excessive hydrogen bonding
- Heat must be absorbed in order to break hydrogen bonds
- Heat is released when hydrogen bonds form
- The high specific heat of water keeps temperature fluctuations on land and in water within limits that permit life
What is evaporation?
The transformation of a substance from a liquid to a gas.
Explain heat of vaporization.
The quantity of heat a liquid must absorb for 1 g to be converted to gas. *(Water has a high heat of vaporization which is another emergent property resulting from the strength of its hydrogen bonds).
What is evaporative cooling?
As a liquid evaporates, its remaining surface cools (the hottest molecules escape as gas). Evaporative cooling helps stabilize temperatures in organisms and bodies of water.
Explain the floating of ice on liquid water.
Ice floats in liquid water because hydrogen bonds in ice are more “ordered” making ice less dense than water. Water reaches its greatest density at 4 degrees C. *(If ice sank, all water would eventually freeze solid making life on earth impossible).
What is the “solvent of life”?
Water
What is a solution?
A liquid that is a completely homogenous mixture of two ore more substances.
What is a solvent?
The dissolving agent in a solution
What is a solute?
The substance that is dissolved
What is an aqueous solution?
When the solute is dissolved in water
What is a hydration shell?
The sphere of water molecules around each dissolved ion.
What is a hydrophilic molecule?
Polar molecules that dissolve readily in water; i.e. Sugars, organic acids, etc. Cotton is hydrophilic but does not completely dissolve.
What is a hydrophobic molecule?
Non polar molecules that are not water soluble; lipids, some proteins, i.e. Vegetable oil
Explain the saying “It’s not the heat; it’s the humidity.”
High humidity hampers cooling by suppressing the evaporation of sweat.
How can the freezing of water crack boulders?
As water freezes, it expands because water molecules move farther apart in forming ice crystals. When there is water in a crevice of a boulder, expansion due to freezing may crack the boulder.
Explain how a hydrogen ion (H+) is formed.
A hydrogen atom participating in a hydrogen bond between two water molecules can shift from one to the other. The hydrogen atom then leaves its electron behind and is transferred as a hydrogen ion, a single proton with a charge of 1+.
Explain how a hydroxide ion (OH-) and a hydronium (H3O+)(H+)is formed.
The water molecule that lost a proton is now a hydroxide ion, which has a charge of 1-. The proton binds to another water molecule, making that molecule a hydronium ion (H3O+)(H+)
What is an acid?
A substance that increases the hydrogen ion (H+)
What is a base?
Any substance that reduces the H+ concentration of a solution.
What is the Ph scale? How do biologists use the Ph scale?
The Ph scale expresses the hydrogen ion (H+) concentration of a solution. This describes whether a solution is acidic or basic. Solutions with a higher concentration of OH- than H+ are known as basic, a solution with more H+ than OH- are known as acidic, and a solution in which the H+ and OH- are equal are said to be neutral (like pure water).
What is the logarithmic scale of the Ph scale? How does the concentration of H+ increase and decrease?
0-14, 7 being neutral. Acids dissociate in water to increase the concentration of H+ in a solution, making it more acidic and expressed in Ph values lower than 7. Bases combine with H+ ions when dissolved in water, thus decreasing the concentration of H+ in a solution, expressed in Ph values above 7.
Explain what an aqueous solution is and the different components.
In any aqueous solution at 25 degrees C, the product of H+ and OH- concentrations is constant at 10^14
[H+][OH-] = 10^14
How is the pH of a solution defined?
By the negative logarithm of H+ concentration, written as:
Ph = -log[H+]
How is a neutral aqueous solution expressed?
[H+] is 10^7
Ph = -(-7) = 7
Explain buffers.
The presence of buffers allows biological fluids to maintain a relatively constant Ph. Buffer minimize changes in concentrations of H+ and OH- in a solution. Most buffers contain a weak acid and its corresponding base, which combine reversible with H+ ions.
Give an example of a Ph regulator in human blood.
When CO2 reacts with water in the blood, it forms H2CO3, carbonic acid. This dissociates to yield a bicarbonate ion, HCO3- and a hydrogen ion, H+. The acid and base work together to maintain equilibrium with each other, maintaining a balanced Ph in the blood stream.
Explain acidification. How is it affecting Earth’s oceans?
When CO2 dissolves in sea water it reacts with H20 and forms H2CO3, which lowers the oceans Ph. About 25% of human generated CO2 is absorbed by the oceans, making the ocean’s water more acidic.
Compared with a basic solution at pH 9, the same volume of an acidic solution at pH 4 has _______ times as many hydrogen ions (H+).
10^5 or 100,000
HCl is a strong acid that dissociates in water: HCl –> H+ + Cl-. What is the pH of .01 M HCl?
[H+] = .01 M = 10^-2 M, so pH = 2
Acetic acid (CH3COOH) can be a buffer, similar to carbonic acid. Write the dissociation reaction, identifying the acid, base, H+ acceptor, and H+ donor.
CH3COOH –> CH3COO- + H+
CH3COOH is the acid (the H+ donor)
CH3COO- is the base (the H+ acceptor)
How does water’s polarity make it a versatile solvent?
Many ionic compounds, as well as nonionic polar molecules are water soluble. A vast variety of compounds dissolve easily when water molecules surround each of the solute molecules; forming strong hydrogen bonds. Even molecules as large as proteins can dissolve in water if they have ionic and polar regions on their surface. Many different kinds of polar compounds are dissolved (along with ions) in the water of such biological fluids as blood, the sap of plants, and the liquid within all cells. Water is the solvent of life.
