1. (5 points) Give a good definition and a specific example or illustration for just one of the following terms:
a) entropy
b) activation energy
c) hydrogen bonding
d) molarity
2. (5 points) A good-sized donut has 500 Calories. If all of those calories are used to warm up your bodily fluids (assume that corresponds to 50 kg of water), then what temperature rise would result?
3. (10 points) Use the attached table of bond dissociation energies to calculate the energy change for the following reaction. Is the reaction exothermic or endothermic?
N2 + 3 H2 -------> 2 NH3
(the fixation of nitrogen, essential for plant nutrition)
4. (20 points) In comparing fossil fuels (e.g., coal) and biomass (e.g., wood) as energy sources, both can be said to be part of the carbon cycle. Explain.
In particular, explain why biomass is considered
to be renewable energy resource while fossil fuels are not.
5. (10 points) Magnesium (e.g., mag wheels) or aluminum (e.g., screen doors) when exposed to air always have a thin coating of oxide on the surface (from reaction with oxygen in the air). Referring to the Periodic Table, explain why aluminum oxide has the particular formula Al2O3 and magnesium oxide has the formula MgO. Are these ionic or covalent compounds?
6. (10 points) Explain why alcohol (C2H5OH) dissolves in water, but its isomer, methyl ether (CH3OCH3) does not. Write detailed structural formulas for each (show every bond, but not necessarily every electron) and explain why they are called isomers.
7. (20 points) Locate where each of the following solutions would be placed on the pH scale shown below.
a) distilled water
b) 0.1 M NaOH
c) 0.005 M HCl
d) a solution with 1 x 10-9 moles of H+ in 0.1 liter
e) a solution with M OH- = 3 x 10-2 moles/liter
pH 1 2 3 4 5 6 7 8 9 10 11 12 13
8. (20 points) A 100 mL sample of lake water is taken for analysis of its acid content. The sample is separated into 10 portions of 10 mL each. To portion A, you add 10 mL of standard base (0.0001 M NaOH ). To portion B, you add 10 mL of standard acid (0.0001HCl ). To portion C, you add just 10 mL of pure water. (The other 7 portions are saved to repeat the experiments.)
A is titrated with standard acid ( 0.0001 M HCl ) and an end point is observed at 9.6 mL.
B is titrated with standard base ( 0.0001 M NaOH ) and an end point is observed at 10.4 mL.
What was the acid content of the original lake water (in moles of H+ per liter)?
What would you expect from titrating portion C? Would you titrate with standard acid or standard base?
(Hint - Identify what is in each of the solutions at each stage, i.e., the number of moles of acid or base. Let the unknown original amount of acid or base be represented by x.)