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Water:

Water:
phase changes:
melting point/freezing point: 0°C
boiling point: 100°C
freezing<->melting
boiling<->condensation
Going directly from solid->gas = sublimation (like dry ice)

Water molecule: H2O, 104.5° apart (look on your iPad)


No interactions with oily things (H-C bonds)
Soap: part H-C bonds, part salts (ionic bonds)


Liquid water has two forms of attraction:
Adhesion: sticks to other surfaces (like adhesive)
Cohesion: sticks to other water molecules (e.g. surface tension)


Capillary action: tug of war between these two forces
How all plants bring water up from their roots
Soap breaks cohesion, so kills capillary action

pH (note small p, large H)
"potency" of Hydrogen
Acids: HCl, HNO3, H2SO4
Bases: KOH, NaOH, Ca(OH)2
Note the pattern?


pH calculations:
Concentration of Hydrogen ions in water is measured by [H+] notation (AP chem folks: [H3O+])
The concentration can be as low as 1ee-14 or as high as 1
since these are really far apart, we use log notation:
100: log10 100=2
1000: log10 1000=3
Not really magic, you see the pattern? Just count the zeroes.


So, really strong acids would have [H+] of 1ee1 while weak acids would have [H+] of 1ee-14
So...
pH is -log10[H+]
or...
Acid: [H+] of 1ee1 would have pH 1
Base: [H+] of 1ee-14 would have pH of 14
That is really all there is to it.
Try these out:
  1. what would be the pH of something with Hydrogen concentration of 1ee-7?
  2. 1ee-14?
  3. 1ee-2?
  4. which of the above are acids and which are bases?
Trick question: which is water: acid or base?
BOTH!
It is right in the middle, pH of 7.
There is another measure called pOH, which is the opposite of pH (recall acids and bases above)
Simple: if pH is 2, the 14-2 = 12 pOH

What they will ask you on the AP exam:
Two acids, one of pH 2 the other pH 4. How much stronger is the pH 2 than the pH 4?
Answer: 100x (4-2=2 which is really 100, or 10^2)

More questions:
If a water sample has [H+} of 1ee4:
  1. is it an acid or a base?
  2. strong or weak?
  3. what is the pH?
  4. what is the pOH?
Last bit:
Ocean acidification happens when CO2 combines with water: (same thing happens in your blood)

CO2 + H2O <-> H2CO3 <-> H+ + HCO3- (note this can go both directions)
See where the H+ comes from?
If you blow into water, you might be able to change the pH (which direction?)
Why would cool water do this better?
What would happen to the pH of your blood if you held your breath (or had a heart attack)? Why?

Fun fact: if you had a bag of chemicals that absorbed CO2, you could breathe back and forth into this bag and not feel like you were holding your breath until you passed out. Early re-breathers were used by SEAL teams so they did not leave bubbles. Many died.

This ocean acidification gets even worse in the second step:

The oceans have absorbed about 30% of the CO2 we have pumped into the atmosphere with fossil fuel burning:


Marine Life and Acidification

A vast majority of marine organisms make their shells from calcium carbonate (CaCO3), or calcite. Many of these animals we are very familiar with, such as clams, oysters, snails, sea urchins, starfish and some plankton, like planktic and benthic foraminifera. Some really important animals that make and provide habitats for other animals, such as corals, also make their skeletons out of calcium carbonate.

Thus, as our oceans become more acidic, animals that build their skeletons and shells from calcite are becoming more stressed. It is becoming increasingly harder for these animals to build their skeletons and shells, and even animals that don’t utilize calcite for their skeletons are responding in a negative manner to ocean acidification.

(This was a question on the 2022 AP exam)