Chapter 16 Test

Tomorrow is the test over Chapter 16. It consists of 23 multiple choice questions. The test will be worth 46 points, so it will be the largest point value of the semester for a test. You will have all of the information that you would have on the AP Chemistry test. A periodic table and all equations. Below are some points that I want to highlight as you prepare for the test.

• Know how to manipulate all equations: pH=-log[H^+] or pH=-log[H3O^+]; pOH=-log[OH^-]; pH+pOH=14.XXX; [H^+][OH^-]=1x10^-14; Ka*Kb=Kw - All equations are linked in some shape or form, so one can be used to find information that is needed for a value to be used in another problem.
• Memorize all six strong acids. Know that all strong bases are metal hydroxides.
• The concept of acid strength can be attributed to the position of the proton in relation to the nucleus of the atom that it is bonded to. HCl, HBr, HI are all strong acids because the protons are far enough from the nucleus and are shielded from the nucleus of the halogen so removal of the hydrogen ion is easier. The bonds between the hydrogen and the halogens are relatively weak. HI is the "strongest" of the strong halogen acids and HCl is the "weakest" of the strong halogen acids because of the reasoning just given. All are still strong acids because of complete dissociation. The remaining halogen, fluorine, makes the weak acid HF. Even though the shared electrons between H and F are closer to F because of its "highest" electronegativity, the bond strength between H and F is strong (4.0 EN - 2.1 EN) and the postition of H to F is close, making it harder for the H^+ to be lost or donated.
• The more oxygens within an oxy-acid, the "stronger" that acid will be. This is due to the increased electronegativity of the added oxygens causing the shared electrons between hydrogen and the element that it is bonded to being farther from hydrogen and closer to the other atom. This concept applies to other elements being added to the acid that have high electronegativities.
• Acids and bases are aqueous, therefore they shift (mess-up) waters equilibrium. Water will act as a base if an acid (strong or weak) is added. Water will act as an acid if a base (strong or weak) is added.
• In a weak base problem, hydroxide is always a product.
• A pH or pOH will give the equilibrium concentration of [H^+] or [OH^-] in a weak acid or weak base problem if asked to determine the Ka or Kb of a substance.
• If a conjugate base of a weak acid is acting as a base, the Kb can be found by dividing Kw by the Ka of the weak acid. Conversely, if a conjugate acid of a weak base is acting as an acid, the Ka can be found by dividing the Kw by the Kb of the weak base.
• The second ionization of a strong polyprotic acid (example: H2SO4) can have an effect on the pH if the initial concentration of the of the acid is relatively low. The second ionization will have little to no effect on the pH if the initial concentration is large ( 1 molar or above).
• A second equilibrium system can be effected by a primary equilibrium system. The primary equilibrium equilibrium system can produce ions that will effect the ability of the secondary equilibrium system to shift right.
• A secondary system can have an effect on pH if its Ka is close to the Ka of the primary equilibrium system and the the inititial concentration of the secondary equilibrium system is large. The secondary equilibrium system will have NO effect on pH if the Ka of the second system is much lower than the first system Ka and the initial concentration of the secondary system is relatively low or close the initial concentration of the primary equilibrium system.
• Since the test is multiple choice, answer choices will be given that are close to each other. Always check "x" values against the initial concentrations to ensure that it meets the 5% threshold. If not with 5% dissociation, use the quadratic formula to get the most acurate value.
• Consider the source of each ion in a salt (ionic compound) when determining the acidic or basic properties of a a salt. A strong base source with a weak acid source will cause a salt to be basic. A weak base source with a stong acid source will cause a salt to be acidic. A strong base source with a strong acid source will cause the salt to be neutral. If a weak base source is with a weak acid source, the solution will be neutral if the Ka and Kb values are equal. If the Ka of the conjugate acid exceeds the Kb of the conjugate base, the solution will be acidic and vice versa.

Come and see me early in the morning if you have any questions. Have a good night.

Acidic Nature of Highly Charged Metal Ions Quiz

Please complete the quiz below for tomorrow, Tuesday, March 15th, 2011. All "highly" charged (+2 or >) metal ions in an aqueous solution are acidic in nature. This is due to the metal being able to hybridize its outer orbitals (sp^3; sp^3d; sp^3d^2) and act as a Lewis Acid (electron pair acceptor). The waters are good Lewis Bases (electon pair donors) with the two non-bonding electron pairs attached to the oxygen of the water molecule. The highly charged metal ion will cause the shared electron between oxygen and hydrogen to be much closer to the oxygen, thus making the ability of a hydrogen to leave the complex ion much better.

The complex ion in the question, hexaaqua aluminum ion, would be octahedral in shape with six ligands (waters) surrounding the central aluminum ion. The hybridization of the aluminum ion would be sp^3d^2. The question asks that you write a dissociation reaction for the I.C.E table, so make sure to show Al(H2O)6^+3 losing a proton and show the resulting conjugate base.

Beginning of Chapter 16

The WebAssignment for Chapter 16 is ready to go. I would advise that you print off a copy of the assignment because I am going to use problems from WebAssign as my focus for discussion in class. The WebAssignment is quite large, so you would be wise to constantly work on the assignment so you are not overwhelmed at the end of the Chapter. We will finish Chapter 16 prior to spring break. I have also posted the Power Point for Chapter 16 on the Events Calendar of the class website under the date of March 1st, 2001. You may download it and print it off if you choose.