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