Chapter 3 - Water and Life Flashcards
What is meant by water being a polar molecule?
It’s overall charge is unevenly distributed: oxygen has partial negative charge and each hydrogen has a partial positive charge.
What are the polar covalent bonds in water?
Electrons spending more time around O than H atoms.
What are the hydrogen bonds in water?
Slightly positive hydrogen is attracted to slightly negative oxygen of a nearby molecule.
What are the four emergent properties of water?
1) Cohesion of water molecules
2) Moderation of Temperature
3) Evaporative Cooling
4) Ice floats - expansion of water upon freezing
What are 3 characteristics of the cohesion of water molecules?
1) Cohesion
2) Surface Tension
3) Adhesion
Why do molecules stay close together?
Hydrogen bonding.
What is adhesion?
Clinging of one substance to another.
Ex. Water from roots of trees reaches leaves.
What is surface tension?
A measure of how difficult it is to stretch or break the surface of a liquid.
Ex. Water striders
What do cohesion, surface tension and adhesion all have in common?
Interactions between water molecules, hydrogen bonds.
How does water moderate temperature?
By absorbing heat from air that is warmer and releasing the stores heat to air that is cooler.
What is kinetic energy?
Anything that moves - energy of motion.
The total thermal energy of a body of matter depends on the matters _____.
Volume.
What is thermal energy?
Kinetic energy associated with the random movement of atoms or molecules.
What is temperature?
Measure of heat intensity that represents the average kinetic energy of the molecules in a system.
Does a swimming pool or pot of coffee contain more thermal energy?
The swimming pool because it has a greater volume.
When two objects of different temperatures are brought together, thermal energy passes from the _____ object to the ______ object.
Warmer/cooler
What is heat?
Thermal energy in transfer from one body of matter to a other.
Or measure of the total kinetic energy of material due to molecular motion.
What is the specific heat of a substance?
Amount of heat that must be absorbed or lost for 1g of the substance to change it’s temperate by 1 degree C.
Because of the high specific heat of water, water temperature will change _____ when it absorbs a given amount of heat.
Less.
What can waters high specific heat be attributed to?
Hydrogen bonding capacity.
What must be absorbed to break hydrogen bonds before the water molecules can move faster.
Heat.
What must be given off to make hydrogen bonds?
Heat.
What happens when water cools slightly?
Many additional hydrogen bonds form, thereby releasing a considerable amount of energy in the form of heat.
What is the relevance of waters high specific heat to life on earth?
A large body of water can absorb and store a huge amount of heat from the sun, warming up by a few degrees in the day and absorbing and storing large amounts of heat that is released at night. Gradual cooking can warm the air.
What does the specific high heat of water moderate?
Air temperatures, ocean water, and organism temperatures. (Most living things 79-95% water)
What is vaporization?
Phase change from liquid to gas.
What is condensation?
Phase change from gas to liquid.
If liquid is heated, the average kinetic energy of molecules _____ and the liquid evaporates more ______.
Increases/rapidly.
What is heat of vaporization?
Amount of heat required for 1g of a substance to go from liquid state to gaseous state.
Why does water have a high heat vaporization? (25degrees = 580cal)
Because of the hydrogen bonds that must be broken before molecules can leave the liquid state.
Why does evaporative cooling occur?
The “hottest” molecules, those with the greatest kinetic energy are most likely to leave as a gas.
What happens when the most energetic molecules leave?
Decline or cooling in temperature.
Water is _____ dense as a solid than as a liquid.
Less.
Solid - liquid - gas the density decreases with the exception of…
Water.
What is the cause of water expanding and becoming less dense as a solid?
As substances cool they contract. As molecules lose energy they move closer together. (Warmer-they expand) contraction of molecules allows hydrogen bonds to form.
What happens to water molecules at 0 degrees?
Water freezes- molecules are not moving enough to break hydrogen bonds and molecules become locked in a crystal lattice with the formation of 4 hydrogen bonds.
Ice is ___ less dense than liquid water at 4 degrees Celsius.
10%
At what temperature are the hydrogen bonds in water molecules broken?
Above 0 degrees
What is a solution?
A liquid that is a homogenous mixture of two or more substances.
What is a solvent?
Dissolving agent.
What is solute?
Substance that is dissolved.
What is an aqueous solution?
Solution in which water is the solvent.
What makes water a versatile solvent?
Polarity of water molecules.
Why does water make an excellent solvent for polar and ionic substances?
Because it has charged regions.
Water is a poor solvent for what kind of substances?
Non polar and non ionic substances. (Hydrophobic)
Water is a good solvent for what types of substances?
Polar and ionic. (Hydrophilic)
How does water dissolve materials?
By forming a hydration shell around that material and overcoming the charge (electrostatic) interactions within the material.
What is a hydrophilic substance?
“Water loving” attraction to water. But can be hydrophilic and not dissolve. Ex cellulose in cotton.
What allows water transport to occur in plants?
Adhesion of water to hydrophilic walls.
What is a hydrophobic substance?
Repels water. Ex. Oil. Cell membranes.
What is a mole?
Convenient chemical mass unit. 1=avogadros number.
What is molecular mass?
Sum of all masses of all atoms in a molecule.
How many Dalton’s are in 1 gram?
6.02 x 10^23 Dalton’s.
How would you make a L o solution consisting of 1 mil of sucrose dissolved in water?
Measure out 342 (molecular mass) grams of sucrose then gradually add water + stirring until dissolved.
What is molarity?
Measure of concentration - the number of moles of solute/L of solution.
What is the mass of one mole of NaOH?
40.00g/mole
How many grams of NaOH are in 1L of a 2.0M solution of NaOH?
8 grams of NaOH?
What are the products of water molecule dissociation?
2H20 = OH- and H3O+
Water dissociates to a hydroxide ion and a hydronium ion?
An acid is a substance that ____ the hydrogen ion concentration in a solution.
A base is a substance that _____ the hydrogen ion concentration in a solution.
Increases/decreases.
An acidic solution has higher ____ than ____.
H+ than OH-
A basic solution has higher ____ than ___.
OH- than H+
A solution I’m which H+ and OH- concentrations are equal are said to be…
Neutral.
How can you tell what are strong acids and strong bases?
Dissociate completely. ➡️
How can you tell what are weak acids and weak bases?
Undergo incomplete or reversible dissociation. ➡️⬅️
In any aqueous solution at 25 degrees Celsius, the product of H+ and OH- is _____.
Constant. [H+][OH-] = 10^14
If a solution has a pH of 3, what are the concentrations of H+ and OH-?
Solution.
What is a buffer?
Substances that minimize changes in the concentrations of H+ and OH- in a solution. Can either accept or donate H+.
Buffers are usually ____ acids or bases that combine reversible with hydrogen ions.
Weak.
When the pH increases there is a shift in the equilibrium to the _____.
When the pH decreases there is a shift in the equilibrium to the _____.
Right/left.
Why does water takes a lot more heat energy to change the temperature of water or make it vaporize?
Because individual water molecules are polar, and they stick together by means of hydrogen bonds.
