Chapter 3 Flashcards
Water Molecule
Shaped like a V. It’s two hydrogen atoms joined to the oxygen atom by single covalent bonds. Oxygen is more electronegative than hydrogen, so electrons of the covalent bonds spend more time close to oxygen than to hydrogen, making the bonds polar covalent bonds.
Polar Molecule
Overall charge of molecule is unevenly distributed.
The properties of water arise from…
Attractions between oppositely charged atoms of different water molecules: The slightly positive hydrogen of one molecule is attracted to the slightly negative oxygen of a nearby molecule. The two molecules are thus held together by a hydrogen bond.
Four emergent properties of water that contribute to Earth’s sustainability as an environment for life:
Cohesive behavior
Ability to moderate temperature
Expansion upon freezing
Versatility as a solvent
Cohesion
The linkage together of like molecules, often by hydrogen bonds.
Adhesion
The clinging of one substance to another.
Surface tension
A measure of how difficult it is to stretch or break the surface of a liquid.
Kinetic Energy
The energy of motion
Thermal energy
The kinetic energy associated with the random movement of atoms or molecules.
Difference between temperature and thermal energy.
Temperature is a measure of energy that represents the average kinetic energy of the molecules in a body of matter, regardless of volume, whereas the total thermal energy depends in part on the matter’s volume.
How do hydrogen bonds react to heat?
Absorbing heat: Breaks hydrogen bonds.
Releasing heat: Forms hydrogen bonds.
Acid
A substance that increases the hydrogen ion concentration of a solution.
Base
A substance that reduces the hydrogen ion concentration of a solution.
pH
Concentration of hydrogen ion (H+)
How does water moderate temperature?
By absorbing heat from air that is warmer and releasing the stored heat to air that is cooler.
Heat
Thermal energy in transfer from one body of matter to another.
A calorie
Is the amount of heat it takes to raise the temperature of 1 g of water by 1•C.
Kilocalorie
Is the quantity of heat required to raise the temperature of 1 kg of water by 1•C.
Joule (J)
1J = 0.239 calories (cal)
One cal = ___ J
4.184
Specific heat
The amount of heat that a substance must absorb or lose for 1 g of that substance to change its temperature by 1•C.
Why does water have high specific heat?
Heat is first used to disrupt hydrogen bonds instead of getting molecules to move faster.
Vaporization/ Evaporation
Occurs when molecules move fast enough to overcome the attraction to other liquid molecules.
Heat of vaporization
Is the quantity of heat a liquid must absorb for 1 g of it to be converted from the liquid to the gaseous state.
Evaporative cooling
Occurs because the “hottest” molecules are the most likely to leave as gas.
As a solid, water is ___________ than as a liquid
less dense
When water solidifies, it
Expands
Why does water expand when below 4•C?
Because of hydrogen bonds. The molecules are moving too slowly to break the hydrogen bonds.
Solution
A liquid that is a homogenous mixture of two or more substances.
Solvent
The dissolving agent of the solution.
Solute
The substance that is dissolved.
Hydration shell
The sphere of water molecules around each dissolved ion. For example, sodium chloride.
Molecular mass
The sum of the masses of all the atoms in a molecule.
1 mole (mol) Avogadro’s number
6.02 X 10^23 daltons = 1 gram
Molarity
The number of moles of solute per liter of solution
- Used for aqueous solutions
What happens when a hydrogen atom participating in a hydrogen bond between two water molecules shifts from one molecule to another?
-The hydrogen atom leaves its electron and a Hydrogen ion (H+) is transferred.
- The water molecule that lost a proton is now a hydroxide ion (OH-)
- The proton (H+) bonds to another water molecule, making that molecule a hydronium ion (H3O+)
Acidic solution
Has more H+ than OH-
In a neutral solution at 25•C…
[H+] = ____
[OH-] = _____
______
[H+] = 10^-7 M
[OH-] = 10^-7 M
[H+][OH-] = 10^-14 M
pH formula
pH = -log [H+]
For a neutral aqueous solution, [H+] is 10^-7 M, giving us a pH of…
-log 10^-7 = -(-7) = 7
pH declines as H+ concentration increases
True
The lower the pH…
The more acidic
Buffer
Is a substance that minimizes changes in the concentrations of H+ and OH- in a solution.
How does a buffer work?
It accepts H+ when they are in excess (within the solution) and donates H+ when they have been depleted (to the solution)
Most buffers are
Acid/base pairs
H2CO3
Buffer that donates H+
HCO3-
Buffer that accepts H+
Ocean acidification
Occurs when CO2 dissolved in seawater, which forms carbonic acid which lowers ocean pH
