2.3 Chemistry of Water Flashcards
What is an acid?
a substance that releases hydrogen ions when they dissociate in water
What is a base?
a substance that either takes up hydrogen ions or releases hydroxide ions
What is the pH scale?
used to indicate the acidity or basicity (alkalinity) of solutions
What is a buffer?
a substance that keeps pH within normal limits
Why do buffers resist pH changes?
they can take up excess hydrogen ions or hydroxide ions
What is the pH of our blood when we are healthy?
7.4, just slightly basic (alkaline)
What happens if our blood pH drops to about 7?
acidosis
What happens if our blood pH rises to about 7.8?
alkalosis
Why is pH stability possible?
the body has built-in mechanisms to prevent pH changes, buffers are the most important of these mechanisms
What does blood always contain a combination of?
carbonic acid and bicarbonate ions
Why is a weakly dissociating acid/base a better buffer than a strongly dissociating one?
a weakly dissociating acid/base re-forms quickly, enabling it to take up excess hydrogen or hydroxide ions
What helps water molecules absorb heat without causing a great change in temperature?
the many hydrogen bonds that link water molecules together
Why is water a solvent?
- due to its polarity, water facilitates chemical reactions inside and outside organisms
- it dissolves a great number of substances that contain ionized atoms or polar molecules
When does condensation occur?
when the temperature of the gas cools below 100 degrees Celsius
Which state of water allows aquatic organisms to remain in a lake when winter temperatures are below 0 degrees Celsius? How?
solid state: frozen water
- as liquid water cools, the molecules come closer together
- below 4 degrees (including 0 degrees freezing point), the water forms a regular crystal lattice that is rigid and has more space between molecules, making it less dense than liquid and causing it to float (water expands when it freezes)
- the floating ice acts as an insulator to prevent water below from freezing
What is cohesion’s role in plants?
tension is created that pulls a water column up from the roots
What is adhesion’s role in plants?
helps prevent water column from breaking apart
Why does water exhibit adhesion?
its positive and negative poles allow it to adhere to polar surfaces
What do the hydrogen bonds in water do?
helps water absorb heat without a great change in temperature
What is surface tension?
the tightness across the surface of water caused by the polar molecules pulling on each other
What is a calorie?
the amount of heat energy needed to raise the temperature of 1 g of water by 1 degree Celsius
How many calories of heat energy does it require to convert 1 g of the coldest liquid water to ice?
80
water holds on to its heat and its temperature falls slower than that of other liquids
What other roles do cohesion and adhesion contribute?
- water’s role as a lubricant
- transport of water in plants
Why is water an excellent transport system?
cohesion and adhesion allow water to fill a tubular vessel
When is there greater surface tension?
- stronger force between molecules
- hydrogen bonding
- cohesion
Why do multicellular organisms rely on external water?
they contain internal vessels through which water transports nutrients and wastes
Why do unicellular organisms rely on external water?
to transport nutrients and waste molecules
Why is cohesion apparent in water?
water flows freely and yet water molecules don’t separate from each other, they cling together because of hydrogen bonding
How does an ion dissociate in water?
in an ionic solution,
- negative ends are attracted to metals
- positive ends are attached to non-metals
What does the ocean do during the summer? During the winter?
summer: absorbs and stores solar heat
winter: slowly releases this heat
Water’s high heat of vaporization gives animals an efficient way to do what?
release excess body heat
when an animal sweats or gets splashed, body heat is used to vaporize the water and cools the animal
Why does water have a high heat of vaporization?
hydrogen bonds must be broken before water boils and changes to a vaporized state
How many calories of heat energy is required to convert 1 g of the hottest water to a gas?
540
Because the temperature of water rises and falls slowly, what are organisms better able to do?
maintain a normal internal temperature and are protected from rapid temperature changes
What is a solution?
a mixture that forms when one substance dissolves another
What is a solvent?
a substance that dissolves another substance
What is adhesion?
a characteristic of water where water molecules stick to other surfaces
What is evaporation?
the process by which liquid changes to gas
What is condensation?
the process by which a gas changes to a liquid
What is cohesion?
a characteristic of water where water molecules cling together
What is a solute?
a substance dissolved by a solvent
What does hydrophilic mean?
molecules that can attract water
What does hydrophobic mean?
non-ionized and nonpolar molecules that cannot attract water
What are the 6 properties of water?
- has a high heat capacity
- has a high heat of vaporization
- is a solvent
- molecules are cohesive and adhesive
- has a high surface tension
- frozen is less dense than liquid
What percentage of water are organisms composed of?
70-90%
What would happen without hydrogen bonding between water molecules?
- water would change from a solid to liquid state at -100 degrees
- water would change from a liquid to gaseous states at -91 degrees
- this would make most of the water on Earth steam, and life unlikely
What percentage of water is the liquid portion of our blood and what does it do?
90%
transports dissolved and suspended substances throughout the body
How does cohesion and adhesion contribute to the transport of water in plants?
a plant contains as system of vessels that reach from the roots to the leaves
the roots of plants absorb water while the leaves lose water through evaporation
water evaporating from the leaves is immediately replaced with water molecules from the vessels of the plant
