Chapter 3 - Water and Life Flashcards
Four of water’s properties that facilitate an environment for life are…
- Cohesive behavior
- Ability to moderate temperature
- Expansion upon freezing
- Versatility as a solvent
Cohesion
The linking together of like molecules, often by hydrogen bonds.
Adhesion
The clinging of one substance to another, such as water to plant cell walls by means of hydrogen bonds.
Surface tension
The measure of how difficult it is to stretch or break the surface of a liquid. Water has a high surface tension because of the hydrogen bonding of surface molecules.
How does Water Moderate Temperature?
- Water absorbs heat from warmer air and releases stored heat to cooler air
- Water can absorb or release a large amount of heat with only a slight change in its own temperature
Heat
A measure of the total amount of kinetic energy due to molecular motion
Temperature
Measures the intensity of heat due to the average kinetic energy of molecules.
Calorie (cal)
the amount of heat required to raise the temperature of 1 g of water by 1°C.
Joule (J)
unit of energy where 1 J = 0.239 cal, or 1 cal = 4.184 J
Specific heat
The amount of heat that must be absorbed or lost for 1 g of that substance to change its temperature by 1ºC.
The specific heat of water is…
1 cal/g/ºC Water resists changing its temperature because of its high specific heat. This minimizes temperature fluctuations to within limits that permit life.
Water has a high specific heat because…
– Heat is absorbed when hydrogen bonds break – Heat is released when hydrogen bonds form
Heat of vaporization
The heat a liquid must absorb for 1 g to be converted to gas.
Evaporative cooling
The process in which the surface of an object becomes cooler during evaporation, a result of the molecules with the greatest kinetic energy changing from the liquid to the gaseous state. Evaporative cooling of water helps stabilize temperatures in organisms and bodies of water.
Ice floats in liquid water because…
Hydrogen bonds in ice are more “ordered,” making ice less dense.
Water reaches its greatest density at…
4°C
Solution
A liquid that is a homogeneous mixture of substances.
Solvent
The dissolving agent of a solution.
Solute
The substance that is dissolved.
Aqueous solution
A solution in which water is the solvent.
Water is a versatile solvent due to its…
polarity, which allows it to form hydrogen bonds easily.
Hydration shell
This forms when an ionic compound is dissolved in water. Each ion is surrounded by a sphere of water molecules.
Can water dissolve Water can also compounds made of nonionic polar molecules?
Yes. Even large polar molecules such as proteins can dissolve in water if they have ionic and polar regions.
Hydrophilic Substance
A substance that has an affinity for water.
Hydrophobic substance
A substance that has does not an affinity for water. Oil molecules are hydrophobic because they have relatively nonpolar bonds.
Colloid
A stable suspension of fine particles in a liquid
Molecular Mass
the sum of all masses of all atoms in a molecule.
Numbers of molecules are usually measured in…
moles, where 1 mole (mol) = 6.02 x 1023 molecules
Avogadro’s number and the unit dalton were defined such that…
6.02 x 1023 daltons = 1 g
Molarity (M)
The number of moles of solute per liter of solution.
Hydrogen ion
A hydrogen atom in a hydrogen bond between two water molecules can shift from one to the other. The hydrogen atom leaves its electron behind and is transferred as a proton, or hydrogen ion (H+).
Hydronium ion
A hydrogen atom in a hydrogen bond between two water molecules can shift from one to the other. The molecule with the extra proton is now a hydronium ion (H3O+), though it is often represented as H+.
Hydroxide ion
A hydrogen atom in a hydrogen bond between two water molecules can shift from one to the other. The molecule that lost the proton is now a hydroxide ion (OH–).
Water is in a state of dynamic equilibrium in which water molecules dissociate…
at the same rate at which they are being reformed
Concentrations of H+ and OH– are _____ in pure water.
equal. Adding certain solutes, called acids and bases, modifies the concentrations of H+ and OH–. Biologists use something called the pH scale to describe whether a solution is acidic or basic.
acid
any substance that increases the H+ concentration of a solution. Acidic solutions have pH values less than 7.
base
any substance that reduces the H+ concentration of a solution. Basic solutions have pH values greater than 7.
In any aqueous solution at 25°C the product of H+ and OH– is constant and can be written as…
[H+][OH–] = 10–14
The pH of a solution is defined by…
the negative logarithm of H+ concentration, written as pH = –log [H+]
For a neutral aqueous solution, [H+] is 10–7, so…
pH = –(–7) = 7
Most biological fluids have pH values in the range of…
6 to 8. The internal pH of most living cells must remain close to pH 7.
Buffers
substances that minimize changes in concentrations of H+ and OH– in a solution. Most buffers consist of an acid-base pair that reversibly combines with H+.
ocean acidification
The process where CO2 dissolves in sea water to form carbonic acid. CO2 is the main product of fossil fuel combustion. About 25% of human-generated CO2 is absorbed by the oceans. As seawater acidifies, H+ ions combine with carbonate ions to produce bicarbonate. Carbonate is required for calcification (production of calcium carbonate) by many marine organisms, including reef-building corals.
Acid precipitation
rain, fog, or snow with a pH lower than 5.2. The burning of fossil fuels is a major source of sulfur oxides and nitrogen oxides. These compounds react with water in the air to form strong acids that fall in rain or snow. Acid precipitation damages life in lakes and streams and changes soil chemistry on land.
