Chapter 19 Practice Sheet

Answers: 1. Each of the metals in the complex ions give have CN=4 and a charge of +2. Each is a square planar geometry. 2. d10/zero, d3/3, d8/2, d7/3 unpaired d electrons

LEWIS acids and bases--no conjugates here!

Gilbert N. Lewis is famous for many things, among them is his definition of acid/base chemistry. A Lewis acid is electron deficient. Generally, transition metal cations are considered good Lewis acids. A Lewis base is electron-rich and after collision, can stick to a Lewis acid through sharing an unbonded pair of electrons. When talking about transition metal chemistry, Lewis bases are the ligands that coordinate (bond or stick) with the metal cation. Electron-pair suppliers can come from molecules that contain an atom with a nonbonded lone pair -- such as N in NH3, N in en, O in H2O. Electron-pair suppliers can also come from anions in solution -- such as O in ox, Cl-, N in CN-. Chelating ligands are long and flexible enough to be polydentate. Both en and ox are both important examples of bidentate ligands. They act as Lewis bases and coordinate to a metal in two positions. When Lewis acid/base chemistry happens between a transition metal cation and ligands in aqueous solution, the result is a complex ion, often with a beautiful color. The formation of complex ions is reversible and so a K value (Kf) can describe the equilibrium composition of the mixture of Lewis acid, Lewis base, and the complex ion.

The Intersection of Science and Religion

Hi everyone!

If you made it through the snow to see Dr. Francl's presentation on how she connects her faith to her work in chemistry, you heard quite a great talk! If you missed it, it is definitely something to look into if you are interested!

I thought it was really interesting that Dr. Francl clarified that it's not just that science and religion mesh at any singular points, and it's not that only certain parts of science and religion work together - but rather, that science and religion are completely related. God has created everything, and we as Christians can really look at the world as God's word. By learning and understanding the world, we can learn about God's greatness and can really learn how to fit our faith into our love of science!

Kayli

Weak Bases in Search of H+

Bases move around looking for a partially positive H to snag as H+. H+ is welcome to take the spot at a lone pair site inherent to a weak base (like on N as part of an amine) or a vacant spot by attraction to a negative charge (on anions). If a base collides with the H part of an acid, the base's ability to steal the H+ away is assessed by the value of Kb. A large Kb means the base is a serious thief, a collector of H+. The smaller the Kb (and larger the pKb) means the acid doesn't have to worry too much about acting as an acid. The Kb of the anions of strong bases are so low, that those anions are essentially ineffective as bases (weaker than weak). They are referred to as spectator ions. Can you list the anions of the strong bases you have memorized?

Talking Chemistry

I have begun to look at the homework for next Friday, and it appears to be similar to what we have been practicing in class. If any of you have questions or would like an explanation of how to do something, please comment or something and we can figure out an answer!!
Dr. Bundens does love when we talk chemistry.

"Practice pH" answers

Here are the answers (and some other thoughts) to the worksheet on pH calculations: 1. [H+] = 2.5 x 10-6 M while [OH-] = 4.0 x 10-9 M. There are two ways of figuring out [OH-]... first, convert pH to pOH and proceed or second way, use [H+] and Kw to get it. Try both ways and become an expert! Note: Rain water is naturally acidic due to various gases in the air (like CO2) that become weak acids when hydrated in clouds. (Recall: Dry ice (CO2) becomes carbonic acid (H2CO3) when bubbled through water :-). "Acid Rain" is when pH is lower than about 5.0 or 4.7. This happens when moisture in the air reacts with specific gases like SO2 and NO2 to form Strong acids (sulfuric and nitric). SO2 is produced when burning coal in many of our nation's power plants and is of real concern in producing Acid Rain. 2. pH = 14.8. Strong base!! Yes, you can have pH greater than 14 and even less than zero (negative!). The pH scale extends in both directions. For this question, there are two ways to get pH from [OH-]... first, take pOH and subtract from 14, or second way, get [H+] with Kw and take pH. Which way do you prefer??

Le Chatelier is fun to say!

Disturb a stable chemical equilibrium system, and you'll put it in opposite world. Le Chatelier observed that the system wants to re-store itself to a happy equilibrium balance and will do so by minimizing the disturbance. Don't we all want this? Balance, harmony, peace, with minimal disturbances... If you increase the pressure on an equilibrium system containing gases, then the road to re-storing equilibrium necessitates relieving at least some of the pressure if possible. Do this by making fewer molecules of gas in the closed mixture. If you crank up the heat on a reversible reaction that has worked so hard to achieve equilibrium status, then it will counter by absorbing some of the heat to promote the product of an endothermic direction. Products of endothermic reactions have absorbed more heat energy than its reactants. So then, what happens if you coooool down a reversible reaction? How will the substance counter this disturbance in order to re-establish an equilibrium balance? If you remove product from an equilibrium reaction, then when equilibrium is restored, the composition will have more product than there was before the disturbance. Removing product "favors" product formation. Removing reactant "favors" reactant formation. The more you remove, the more you'll form (but still less than you remove -- there is no *exact* opposite behavior). "Shifting" means "Favoring" a direction of change... changing into more products than in the original equilibrium or changing into more reactants than in the original equilibrium. It is the composition of the mixture that "shifts"! Of all these disturbances, ONLY TEMP can change the value of the equilibrium constant K. The other disturbances can change the product-to-reactant composition, but the overall value of K remains the same -- 2/1 is the same as 12/6 and 20/10, but each ratio is still 2 overall.

Le Chatelier's Principle

Hey everyone,

So today's lecture was really interesting with Le Chatelier's Principle and the entire concept behind it. It really does make sense how if you increase the concentration of a product, then the concentration of the reactants will then increase while the products decrease in order to maintain that equilibrium constant.

Personally, I kind of like to think of it as a sort of see-saw where if one side goes up, it then must come down while the other side goes up. Not to mention the fact that when you increase the temperature of the system, the endothermic reaction will increase while the exothermic reaction will decrease and vice versa. It truly is a case of where in order to get a certain result you have to do the exact opposite.

Looking forward to seeing you all either tomorrow or Wednesday.

Matt