CHEM1112 Lecture Notes - Lecture 24: Coordinate Covalent Bond, Coordination Complex, Lone Pair

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 ‘transfer’ of one entity to another. In the case of Brønsted-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 ‘hardness’ defined as small highly charged species that are weakly polarizable (Lewis acids). In contrast, ‘softness’ 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 ‘ligands’ 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 Brønsted-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:
ΔG0 = -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-salts’ 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 ΔG 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 ΔG 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 Brønsted-Lowry acids and bases. Support these concepts with your data over the last two weeks and with research. Cite your sources.

Nomenclature lab : will rate answer

Nomenclature lab: will choose best answr

Type I Binary Ionic Compounds

Type I binary ionic compounds contain a metal and a nonmetal AND the metal that is present only forms one type of cation. Metals with only one cation(shaded below with charges). Both the metal and the nonmetal form ions, which is why it is called an ionic compound.

From the following list, cross out those compounds that do NOT belong in the category for Type I binary ionic compounds.

NaCl FeCl2 CaCl2 TiO2 MgO AlBr3 KCl K2S BeF2 Cu2O3 AgCl Zn3N2

Formula and name examples for Type I binary ionic compounds:

KI = potassium iodide BaO = barium oxide ZnF2 = zinc fluoride Na2S = sodium sulfide

Ag3N = silver nitride BeCl2 = beryllium chloride

What type of element is always listed first (metal or nonmetal)? ____________ second? ___________

Is the name of the first element in the compound different from the element? (yes/no)

What is the common ending for all the names? ______________

In zinc fluoride, there are 2 fluoride atoms, are they indicated in the name? (yes/no)

What is the charge on the zinc ion? _______

What is the charge on the fluoride ion? _______

Why do you need one zinc ion and two fluoride ions for the formula for zinc fluoride?

Why do you need two sodium ions for every sulfide ion in sodium sulfide?

Try not to look in your book and determine the rules for naming type I binary ionic compound when given the formula.

Try not to look in your book and determine the rules for writing the formula for a type I binary compound when given the name.

Name each of the type I binary ionic compounds listed in Question 1 of the Type I section in words.

Type II Binary Ionic Compounds

Type II binary ionic compounds also contain a metal and a nonmetal however the metal that is present here can form more than one type of cation. Metals with multiple possible charges are listed in the periodic table as blank. Type II metals are NOT Type I metals. Again, both the metal and the nonmetal form ions, and it is still called an ionic compound. These metals usually only form two different ions.

From the following list, cross out those compounds that do NOT belong in the category for Type II binary ionic compounds.

AlP FeCl2 Ag2O VBr5 CoS SnF2 K3N SrF2 CuBr AuCl3 ZnO HgS

Formula and name examples for Type II binary ionic compounds:

Fe2O3 = iron(III) oxide or ferric oxide FeO = iron(II) oxide or ferrous oxide

CuS = copper(II) sulfide or cupric sulfide CuCl = copper(I) chloride or cuprous chloride

MnO2 = manganese(IV) oxide or manganic oxide MnCl2 = manganese(II) chloride or manganous chloride

What type of element is always listed first (metal or nonmetal)? ____________ second? ___________

Is the name of the first element in the compound different from the element? (yes/no)

What is the common ending for the nonmetal portion of the names? ______________

In the compound FeO, what is the charge on iron? _______

In the compound Fe2O3, what is the charge on iron? ________

What does the Roman number after the metal name represent?

Try not to look in your book and determine the rules for naming type II binary ionic compound when given the formula.

Try not to look in your book and determine the rules for writing the formula for a type II binary compound when given the name.

Name each of the type II binary ionic compounds listed in Question 1 of the Type II section in words.

Type III (Nonmetallic) Binary Compounds

Binary compounds that do not contain metals, sometimes referred to as binary molecular compounds, have covalent bonds instead of ionic bonds. A covalent bond is formed by sharing one or more pairs of electrons. The pair of electrons is shared by both atoms. For example, in forming H2, each hydrogen atom contributes one electron to the single bond.

From the following list, cross out those compounds that do NOT belong in the category for binary compounds containing only nonmetals or metalloids.

CCl4 AlCl3 CO SeF6 SiO2 SrI2 P4O10 TiO2 SeO3 IrCl ZrO2 N2O5

Formula and name examples for Type III binary molecular compounds:

CO2 = carbon dioxide H2O = dihydrogen monoxide

IF5 = iodine pentafluoride BF3 = boron trifluoride

Which element is listed first in the name?

Is the name of the first element in the compound different from the element? (yes/no)

What is the common ending for all the names? ______________

What do the prefixes (di-, mono-, penta-, tri-) in the names above mean?

Is the prefix mono- used when there is only one atom of the first element? (yes/no)

Is the prefix mono- used when there is one atom of the second element? (yes/no)

Try not to look at your book and determine the rules for naming type III binary ionic compound when given the formula.

Name each of the type III binary compounds in Question 1 of the Type III section in words.

Compounds Containing Polyatomic Ions

Polyatomic ions are ions that as a group have a set charge. Polyatomic ions are usually recognized in a formula by the grouping of more than one nonmetal elements after a metal. Your book has a table listing polyatomic ions. Use your book’s table to fill in the following table with the appropriate names/formulas of the polyatomic ions.

Polyatomic ions containing oxygen (oxyanions or oxoanions) are somewhat special.

carbonate = CO3-2

Match the location of carbon on the periodic table with the two figures on the right.

What number is in the carbon location on the left figure? To what does this number refer?

What number is the carbon location on the right figure? To what does this number refer?

What element must all oxyanions contain?

What is the ending of the name of the ion determined from these tables?

Determine the formula for the following oxyanions using the figures above. Phosphate _________ Silicate ________ Bromate ________ Iodate ________ Sulfate ________ Nitrate ________

Review Table

Use your knowledge of Type I and Type II metals as well as the appropriate polyatomic name/formula to fill in the following table.

Acids

Acids are compounds that when dissolved in water, produce hydrogen ions (H+). Naming acids can be tricky. Use the following figure to determine how to name an acid.

FG02_27

Given that the ion formula is NO2-1, how can one determine the name of the ion, acid formula, and acid name?

Ion name:

What is the formula for nitrate?

Is NO2-1 the nitrate ion or the nitrite ion?

Acid formula:

According to the figure above, what ion must be added to create an acid? What is the charge of that ion?

How many of the hydrogen ions must be added to NO2-1 to make a neutral acid (zero charge)?

What is the chemical formula for the acid created when hydrogen ion(s) are added to NO2-1?

Acid name:

Based on your answer to Question 1 above, does the name for the NO2-1 ion end in –ite or –ate?

Name the acid, HNO2.

Fill in the following acid table: