Chemistry 2223B Lecture Notes - Lone Pair, Chch-Dt, Benzene

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7 Mar 2014

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Chemistry 2213a fall 2012 western university. One of the most important classes of reactions in chemistry and biology is the. Br nsted-lowry acid-base reaction, which is a proton-transfer reaction. For example, caffeine can be protonated by the acid in the stomach. According to the br nsted-lowry definition of acids and bases, acids are proton donors, and bases are proton acceptors. Onnnno+h2o+h3oonnnhnohah+ab+hbhacidconjugatebasebaseconjugateacid every proton-transfer reaction must have an acid and a base. If one of these is water (an amphiprotic species), we would more properly write: In the above, the acid and the base are shown as neutrally charged species, but they do not need to be neutrally charged: use of arrows. Proton-transfer reactions involve the movement of pairs of electrons. In organic chemistry, the movement of a pair of electrons is shown using a curved arrow that depicts the origin and the destination of the electrons. Ha+h2oh3o+aforanacid:b+h2obh+ohforabase: other arrows that are used in chemistry are: curved fishhooks,

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.ill AT&T 9:44 AM Back Chem1B-W18-Homework5.pdf [1] This homework assignmenté·due at the begining of class on March 9., 2018, write your answers on a separate piece of paper, and show your work to receive credt Protiem 1 What distinguishes a strong acid from a weak acid7 What distinguishes a strong base from a weak base? Write out examples of the proton-transfer reaction for each as well as the equilibrium expression (K or Ko) tor each ? Wrtie equations Probiem 2 In class we dscussed e autoionization of water, What is an for the autoionization reactions for H-O and H SO Assume that both are pure iquids Problem 3 In class on Friday, we calculated the [HO-1 and [OH in stomach acid at pH 1.5 The average volume of an adult human stomach is 1L. How many H0 ions are present in a human stomach i&the pH is 2.0? How many OH- ions? man body temperatre). Problem4 any equlbnum constant. Min changes with temperature. At 37 â the pH of waner is 6.80. Caloulate the following for pure water at this temperature: b) IOH1 Problems whais a con ate acid-base pair? What is the relationship between the two members of pair? Prettem.6 Draw a Lewis structure ot each of thy tolowing acids. Then, wte balanced aciddssociaton reactions and equibrium expressions for each in water. a) Formic acid, HCOOH b) Chloric acid, HCIO, c) Dihydrogen arsenate, H As0 Probiem Z Dihydrogen arsenate is an ampiprotie substance, meaning tcan both accept and donane a proton Draw Lewis structures of the conjugate acid and the conjugate base of dihydrogen arsenate. Write the balanced base-dissociation reaction and equiibrium expression of dihydrogen arsenate in water Paatina successivo K.'s for polyprotic acids decrease. For thÃ© polyproc phosphoric acid. HAo, K., 7.2 x10. KA6.3 x 10, Ka 4.2 x 10- Draw Lewis structures of each of the species involwed in each acid- dissociation roactonãWhy d0the K.'s decrease for each successi e deprotaraton? Protiem 2 Hypochionous acid, HCIO, has a pka ol 7.54. What are the [Hs0-]. pH. [CO1 and [HCIO] in a 0.115 M solution of HCI0? Problema in a 0 735 M solution a weak acid is 12 5% dssoc ated. a) Calculatemo-1, pHÂ·[OH 1, and pH of the solution. b) Calculate Ka of the acid Problemi! Acetyisaleyic acid (asprin, structure shown to the right). HCæ¤:O4, is the most widely used pain reliever and tever reducer. Find the pH of 0.018 M aqueous aspirin at body temperature (K.: 3.6 x 104 at 37Â°C). Problem12 whyé·aqueous NaF basic but aqueous NaCl neutral? Chit consider the reaction of each anion with water 1 of 1 Previous Dashboard Calendar To Do Notifications Inbox

I want to find the Kn value of Cu(II) and EDTA. I was given the formula kn= [ML4]/[ML3][L]. 12.3 ml of edta was used to tritrate 0.1194 grams of Copper in 50 ml of water. The indicator used was murexide.

At the core of general acid-base theories, there is the concept of âtransferâ of one entity to another. In the case of BrÃ¸nsted-Lowry acid base theory, the transferred entity is the proton, and their transfer processes are widely exploited in chemical methods. In addition to proton transfer, electron pairs can also be donated/shared between donors and acceptors. In this case, an atom/molecule, which can accept a pair of electrons, is referred to as a Lewis acid while the entity donating the pair of electrons is referred to as a Lewis base. The most prevalent Lewis acid-base systems involve metal complexes with vacant nd-orbitals, as well as electron deficient systems including B, Si, Ge, etc. The Lewis acid base theory is also known as the Hard-Soft acid base theory (HSABT) with âhardnessâ defined as small highly charged species that are weakly polarizable (Lewis acids). In contrast, âsoftnessâ is described by species that are larger and highly polarizable species with low charge (Lewis bases).
In the case of metal chemistry, Lewis acid-base theory provides a means to describe the ability of âligandsâ to coordinate to metal ions as well as the stability of metal-ligand complexes. Recall that coordination bonds are the donation/acceptance of lone pairs of electrons to empty metal orbitals to another atom; the definition of Lewis acid-base chemistry! The stability of Lewis acid-base complexes can be described through the stability constant which is analogous to the Ka that describes BrÃ¸nsted-Lowry acidities. Many metal ions can coordinate (bind) many Lewis base ligands in a step-wise fashion according to:
M + L = ML K1 = [ML]/[M][L] Eq. 1
ML + L = ML2 K2 = [ML2]/[ML][L] Eq. 2
ML2 + L = ML3 K3 = [ML3]/[ML2][L] Eq. 3
MLn-1 + L = MLn Kn = [ML4]/[ML3][L] Eq. 4
and for which the free energy for this dissociation reaction is given by:
ÎG0 = -RTLnKn Eq. 5.
where R is the gas constant and T is the temperature in Kelvin.
Figure 1: Left- EDTA. Right- Typical EDTA-transition metal complex.
The ethylene diamine tetraacetic acid ligand (EDTA, a Lewis base) provides a mechanism to probe the Lewis acid strength of various metal complexes (Figure 1). This multi-dentate ligand (multiple Lewis base sites on a single ligand) forms complexes with metals of the form:
Mn+ + Y4- = MYn-4 Eq. 6
K = [MYn-4]/[Mn+][Yn-4] Eq. 7
where Y4- is the EDTA ligand.
In this experiment, the Lewis acid strength for two different metals will be examined by measuring the stability constants for the metal-EDTA complex. Of specific interest is the how the Lewis acid strength of the metal ion correlates with:
1) atomic/ionic radii, 2) oxidation state, 3) electron configuration, and 4) polarizability.
You will determine the stability constants of both a Cu2+- and Zn2+-EDTA complexes as well as the corresponding free energy. Using these data, you will compare the relative Lewis acidities of both metals and describe differences in terms of the metal ion properties described above.
.
Chemicals
CuSO4
ZnSO4
EDTA
Murexide
Instruments
Buret
Experimental
You and your group will determine the concentration and ultimately the free energy of Cu(II) and Zn(II) using the hexadentate chelating ligand, EDTA.
You will be given a ~100 mM standardized solution of EDTA (check the label for exact concentration prior to beginning). You will need to weigh ~0.1 g per metal salt sample. Dissolve the metal salt into 50 mL of DI water. Add 2-3 drops of murexide to your metal. After properly preparing your buret with EDTA, titrate your metal with EDTA. Repeat for a total of 3 titrations per metal.
1. Approximately how much EDTA will you need for each titration assuming the metal-saltsâ masses are accurate?
2. What type of indicator is murexide and what color will its endpoint be?
Post-Lab Questions
1.
a) Using the equations given in the introduction and your titration results, what are the Kn of the EDTA-Copper complex? Show calculations.
b) Using the equations given in the introduction and your titration results, what are the Kn of the EDTA-Zinc complex? Show calculations.
2. What are the corresponding ÎG values for the EDTA-metal complexes? Show your calculations
3. Would copper be considered a hard or soft lewis acid? What about zinc? Describe what makes these metals hard or soft.
4. What trends would you predict for EDTA-metal complex Kn and ÎG values when:
a) going down a row of transition metals of the same oxidation state?
b) of the same transition metal with increasing oxidation state? (For example, Iron can exist as Fe(II), Fe(III), Fe(IV), and higher oxidation states)
5. Discussion (formal report style): Compare and contrast the concepts of Lewis and BrÃ¸nsted-Lowry acids and bases. Support these concepts with your data over the last two weeks and with research. Cite your sources.

Chemistry 2223B Lecture Notes - Lone Pair, Chch-Dt, Benzene

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