Showing posts with label acid. Show all posts
Showing posts with label acid. Show all posts

Monday, May 9, 2011

What is K? (A Mind-Map Style Explanation)


As I had mentioned in the introductary post to this blog, I had a real hard time figuring out what "K" meant until it was finally revealed to me. Even then, I pretty much didn't have the right answer until I took the professor's advice and made a flowchart of what "K" actually is. Here below is a hand-drawn mind-map of K, and represents much of what we learned in Chem II. I apologize in advance for the sloppy penmanship. Part of the assignment required that I write it by hand, rather than make the chart on computer.
Click on image for the Large Version


As you can see, K, as it applies to most of second semester inorganic chemistry, is a thermodynamic constant, and is largely the distilled essence of everything from solubility to electrochemistry, and most points in-between. Despite the fact we were, throughout the semester, educated on the values of Kc, Ka, Ksp, and many other constants, they all are simply different aspects of K. The value in learning this is in finding out exactly how a constant comes into being. I'm sure most of you by now have encountered the Ideal Gas Constant, or Faraday's Constant, Coulomb's Constant. or even Avogadro's Number, and wondered "that's great, and all, very useful stuff to know, but how do these constants come about in the first place?"

Unlike the ones I mentioned, K is a dynamic constant, in that it is not a number that will always be the same. It changes depending on the values fed to it, but the formula, the product of the concentration of right-hand side of the equation, divided by the product of concentrations of the left-hand side of the equation, helps us to understand where constants come from. In these instances, we are developing our own constants each time. It is through this process we begin to unlock the methodology that the giants before us used to establish the static constants (the numbers that are always the same) by applying very much the same principles, using slightly more advanced math, and many, many trials.

This concept was at first so frustrating for me, and later so inspirational, that it resulted in the creation of this blog, and hence, the name, The Daily Constant. It helps us each to remember that it is you who hold the future of scientific breakthroughs in your hand, not those who came before you. They hold the past, but it is up to you to come up with the constants others will use for ages to come, and to unlock the knowledge and additional mysteries it brings.

Saturday, May 7, 2011

Chem II: Final Exam Review (Part 2/4)


1.       Define Equilibrium
a.        The rate of the forward rxn is equal to the rate of the reverse rxn.
b.       The concentration of reactants and products remains constant.
c.        Opposing processes occur at equal rates.
d.       Dynamic.
e.       Has nothing to do with collision.
f.         Examples
                                                               i.      R(evaporation) = R(condensation)
                                                              ii.      R(dissolution) = R(crystallization)

2.       The Equilibrium constant…
a.        Will not tell you the speed of the reaction.
b.       Will tell you the extent of the reaction.
c.        Predicts the direction of the reaction.
d.       Allows to calculate the equilibrium concentrations.

3.       Relate Qc to Kc to Direction of the reaction.
a.        Qc <Kc = reaction goes left to right.
b.       Qc>Kc = reaction goes right to left.

4.       If you reverse and cut in half a reaction…
a.        Kc = [1 / Kc^(1/2) ]

5.       If you increase pressure, volume…
a.        Expands towards the direction of fewer molecules of gas.
b.       Unless there are equal moles on each side.
c.        Adding H2O to a solution…
                                                               i.      …will not affect equilibrium.
                                                              ii.      …will dilute the Molarity.
6.       To find Equilibrium Pressure Kp…
a.        Kp = Kc(RT)^(∆n)
b.       ∆n = (c+d) – (a+b)
c.        R = 0.0821
d.       T = temp in K.

7.       Lewis Acids include:
a.        Something that will accept an electron pair.
b.       Group III (Boron, Aluminum, Galium)

8.       The _____ acid will have the strongest conjugate base.
a.        weakest

9.       Given Hydronium concentration, find pH:
a.        pH = –log (H3O)

10.    Given pH, find Hydronium concentration:
a.        [H3O] = 10^(-pH)

11.    Find Ka given initial concentration and pH:
a.        10^(-ph) = [H+]
b.       ([H+]^2) / Molarity = Ka

12.    What is Hydrolysis?
a.        When an ion reacts with water.

13. 
1.       Strong Acids and Bases:
a.        Are not Hydrolyzed
b.       Do not achieve equilibrium
c.        Strong Bases:
                                                               i.      Include Group IA (except H)
                                                              ii.      Include Group 2B (except Beryllium)
d.       Strong Acids:
                                                               i.      Include
e.       When added together, make a neutral solution.

2.       Ka will favor products if it is _greater_than _10^3_ and reactants if it is _lower_than_10^-3_.

3.       How do you determine if x in ([M]-x) can be neglected?
a.        If [A]/Ka > 100, then x may be neglected.

4.       How do you calculate % Dissociation?
a.        100 * (x dissociated Acid or Base / [M] initial concentration ) 

5.       About Buffers:
a.        Mix a weak acid or weak base and its conjugate.
b.       Water is not a buffer.
c.        Resist a change in pH when adding an acid or a base.
d.       Buffer Capacity is the limited amount the buffer can absorb before a significant change.
e.       Buffer Capacity depends on the number of moles.

6.       What is the Henderson Hasselbach Equation?
a.        pH = pka log ([Base]/[Acid])
b.       pOH = pkB log ([Acid]/[Base])
c.        pka = -log(ka)
d.       Ka = Kw/Kb
e.       Used to calculate the pH of a Buffer Solution.

7.       The second ionization constant:
a.        Is Ka2 = A2-
 
8.       What is the common ion effect? What’s it do? Give examples.
a.        The presence of an ion already present in the solution, based on the LeChatlier Principle.
b.       It causes:
                                                               i.      Suppression/Decrease of Ionization
                                                              ii.      Makes the degree of ionization smaller.
                                                            iii.      Shifts the reaction to the left.
                                                            iv.      Acid/Base is weakened.
c.        Eg. The solubility of silver chloride AgCl is reduced if a solution of NaCl is added.

9.       Amphoteric…
a.        Can act as an acid or a base, but doesn’t need a hydrogen.
b.       Eg. Al2O3

10.    Amphiprotic…
a.        Is Amphoteric but must have a Hydrogen in the formula.
b.       Eg. HSO4

11.    Arrhenius Acid:
a.        Releases H+ in water.
b.       Releases OH- in water.

12.    Br0wnstead/Lowry Acids:
a.        B/L A = proton donor
b.       B/L B = proton acceptor

13.    Lewis Acids and Bases…
a.        LA needs a lone pair of e-.
b.       LB has a lone pair of e- available.

14.    Acid Strength Depends on:
a.        Polarity – the more electronegative the NON-H part of a molecule, the stronger the acid, because H can break away easier.
b.       Bond Strength – Electron radius increases to the right and down. The larger the radius, the weaker the bond, so the stronger the acid.
c.        Oxoacids – The more O in an Oxoacid, the stronger it is.