1. There are six elements essential to life. What are they? Where do elements such as calcium (Ca) and sodium (Na) fit into this picture?
The six building blocks of life are: CHONPS
Ca and Na are considered nutrient cations, which are also important
2. Water is a universal solvent. What properties does it have that make it particularly good at dissolving salts? (Draw a picture if need)
Water is highly reactive, and is a polar molecule with a large dipole moment. Salts dissolve in water when water molecules form a hydrate complex with salts.
3. If I dissolve CaCl2 in water, will the pH of my solution change? Why or why not?
The pH of the solution will not change. Since CaOH is a strong base, and HCl is a strong acid, neither H+ nor OH- is going to be removed from solution.
4. As pH increases, what happens to the concentration of hydrogen ions? Of hydroxide ions?
High pH means low [H+] and high [OH-]
5. Pure water has a pH of 7. Ordinary rain tends to be slightly more acidic, while water that has been in contact with rocks tends to be more alkaline. Why?
Ordinary rain that has been in contact with the atmosphere has come in contact with CO2, which forms the carbonate complex, and acidifies the water. Once this acidic water comes into contact with rocks, there is a cation exchange in which H+ in the water trades places with the mineral cations in the rocks. The result is that the [H+] in this water is decreased, making it more alkaline.
6. Mineral weathering is an important source of most nutrient inputs. Which valuable nutrient will you not find through this process?
7. The dissociation equation of sulfuric acid looks like this:
H2SO4 ---> H+ + HSO4- ---> 2H+ + SO4-2
Is sulfuric acid a strong or weak acid? Why?
Without knowing the dissociation constant Ka of sulfuric acid, one cannot determine if sulfuric acid is a strong acid or not. As it happens
K1 = 2.4 * 106 pKa1 = -6.62
K2 = 1.0 * 10-2 pKa2 = 1.99
The K1 tells us that sulfuric acid is a strong acid.
8. Refer to the graph describing the changes of carbonate as a function of pH for this question:
As you lower the pH (shift to the left), what form does carbonate take and why? Considering that many marine organisms use calcium carbonate (CaCO3), to make their shells, how would an increase in acidity interfere with this process? What would the larger impacts on the ecosystem be as a result of increased ocean acidity?
Carbonate (CO32-) will likely bond with two H+ ions to become H2CO3 as opposed to HCO3- at mid-levels of pH.
As more H+ appears, the CO32- cations will be inclined to bond with the H+, and therefore the CaCO3 in the shells would likely dissolve.
Besides dissolving the CaCO3, acidic waters are not that likely to support life, so more fish and other marine life forms would find it harder to live in a more acidic ocean.