Water Flashcards
What are three pieces of evidence that water is essential to life?
It makes up over 70% of the Earth’s surface, life is aqueous in nature (i.e. most organisms are just like bags of solutions of complex molecules…but 50%-70% water), and most living things still live in water
Why are water molecules “bent”
The central oxygen atom has two unbonded pairs of valence electrons and two electron domains bonded to hydrogen atoms. The most stable arrangement of these four electron domains is a tetrahedral shape in which the hydrogen atoms appear bent.
Why is water polar?
The oxygen atom is more electronegative than the hydrogen atoms, creating two negative dipoles on the oxygen atom and a positive dipole on each hydrogen atom. This separation of charge over the surface of the water molecule makes is polar.
What type of bond exists between water molecules?
hydrogen bond (resulting from strong polarity)
Water has four very important properties that arise from its hydrogen bonding and make it essential to life. What are those?
Cohesion, the density of ice is less than that of liquid water, high heat capacity, and its ability to be a good solvent
What does cohesion mean in the context of water?
Cohesion is water’s tendency to stick to itself due to its strong hydrogen bonds
Name two examples of how cohesion plays a role in nature.
It allows for evapotranspiration (as the water molecules on the surface of leaves evaporate, they pull up water molecules through the stem/trunk of plants and out of the ground, circulating it) and surface tension (the fact that the water molecules on the surface of water are hydrogen bonded to each other and the molecules below them but not the air creates surface tension).
Why is ice less dense than water?
As a liquid, water’s hydrogen bonds are instantaneous and temporary allowing water molecules to be closer together, but as the temperature drops and water freezes, the hydrogen bonds become stiffer and hold the water molecules in a more fixed position with more room between molecules. This make ice less dense.
How does ice’s low density play a role in nature?
Because ice is less dense and floats to the surface of bodies of water, it allows fish and other aquatic life to survive under the surface during the winter.
What does water
s specific heat capacity mean?
It means that it requires a lot of energy to increase water’s temperature.
What are two ways that water’s heat capacity plays a role in nature?
Because water changes temperature less dramatically than land, areas along the water are cooled by being near the water. And when water does evaporate, the molecules with the most kinetic energy are the ones to do so first, so when we sweat the sweat that leaves our skin is taking away heat and cooling us off.
Describe water’s role as a good solvent.
If the solute has enough dipoles on its surface (i.e. it’s polar enough) then water molecules will orient themselves around particles of the solute according to like charges, creating a hydration shell.
Define hydrophilic and give examples
Hydrophilic substances are attracted to water and thus easily dissolved in it. Some examples are substances that are polar or ionic.
Define hydrophobic and give examples
Hydrophobic substances tend to avoid water and don’t dissolve easily in it. Some examples are non-polar and non-ionic substances like oils fats.
How does the fog-basking beetle use hydrophobicity to its advantage>
It has ridges along its back. The tops of the ridges are hydrophilic regions where water collects and the lower areas between ridges are hydrophobic and serve as a slick channel for the water to roll down to the beetle’s head, where it cools it off.
