Lab Midterm

Question 1

What is the difference between a coordination compound and a complex?

Answer 1

A coordination compound is the complex with its neutralizing ion; the complex has a charge

Question 2

What is a monodentate ligand and give examples

Answer 2

A ligand that forms one bond; Water, NH3, SCN-, S2O32-, F-, Cl-, Br-, I-, OH-

Question 3

What is a bidentate ligand and give examples

Answer 3

A ligand that forms two bonds; ethylenediamine (en), oxalate, mercaptol, tartrate ion

Question 4

What is polydentate ligand and give examples

Answer 4

Ligands that form more than one bond; ethylenediaminetetraacetate ion (Y4-, 6 bonds), diethylenetriamine (3), Tripolyphosphate ion (5)

Question 5

Define chelating agent (aka sequestering agent)

Answer 5

Ligands that form two or more bonds to a transition metal ion

Question 6

Define coordination number

Answer 6

The number of bonds between a metal ion and its ligands

Question 7

What is LeChatelier’s Principle?

Answer 7

If an external stress (change in concentration, temperature, etc.) is applied to a system in a state of dynamic equilibrium, the equilibrium shifts in the direction that minimizes the effect of that stress.

Question 8

What is a buffer? Give an example

Answer 8

A buffer resists pH change; consists of a weak acid and its conjugate base or a weak base and its conjugate acid; e.g. acetic acid CH3COOH

Question 9

What is the common-ion effect?

Answer 9

The effect of adding an ion or ions common to those already present in a system at a state of dynamic equilibrium

Question 10

What is array analysis? What are the pros and cons?

Answer 10

To each individual anion, we added reagent and observed whether a chemical reaction takes place (ppt, color change, gas, heat). The approach is fast, but not useful for mixture of ions

Question 11

What type of reaction occurs between Fe3+ and the halides (Br-, I-, Cl-)?

Answer 11

Redox

Question 12

What is a way to test for nitrate in solution? (NO3-)

Answer 12

Brown Ring Test

Question 13

What method was used for Qual I Cations? (Na+, K+, NH4+, Mg2+, Ca2+, Cu2+). What is a negative about this method?

Answer 13

Divide and conquer; it is time consuming

Question 14

What was the procedure for Qual I Cations? (Na+, K+, NH4+, Mg2+, Ca2+, Cu2+)

Answer 14

Mixture of cations -> add group reagent -> separate them into groups -> divide and conquer (separate ions) -> need flow chart

Question 15

Why use a flame test for Na+ and K+?

Answer 15

Na+ and K+ are soluble and cannot be detected by other techniques (acid-base, redox)

Question 16

How do you test for NH4+?

Answer 16

Increase the pH of the solution using NaOH to generate NH3 gas. NH3 is a weak base and can be tested with litmus paper

Question 17

Why did we add oxalate (C2O4) and CO3 to the Qual I cations?

Answer 17

The addition of oxalate and CO3 precipitates out other ions so that you can test for Na+ and K+

Question 18

Qual I: Why not use NaOH instead of NH3?

Answer 18

Because NaOH is a very strong base and NH3 is a weak base, so if NaOH was used it would be outside of the desired pH range

Question 19

Qual I: Why add HNO3 to Cu (s)?

Answer 19

To put Cu back in solution as Cu2+ and carry on the test

Question 20

Define amphoteric and give an example

Answer 20

A substance that can act as an acid and a base; Al(OH)3

Question 21

List the cations that form soluble salts and insoluble salts with OH-

Answer 21

Soluble: NH4+, Sr2+, Ba2+, Group 1A
Insoluble: Most cations

Question 22

List the cations that form soluble salts and insoluble salts with CO3 2-

Answer 22

Soluble: NH4+, Group 1A (except Li+)
Insoluble: Most cations

Question 23

List the cations that form soluble salts and insoluble salts with Cl-

Answer 23

Soluble: Most cations
Insoluble: Ag+, Hg2 2+, Pb2+, Cu+, Tl+

Question 24

List the cations that form soluble salts and insoluble salts with I-

Answer 24

Soluble: Most cations
Insoluble: None

Question 25

List the cations that form soluble salts and insoluble salts with NO3-

Answer 25

Soluble: Most cations
Insoluble: None

Question 26

List the cations that form soluble salts and insoluble salts with NO2-

Answer 26

Soluble: Most cations
Insoluble: None

Question 27

List the cations that form soluble salts and insoluble salts with oxalate, C2O4 2-

Answer 27

Soluble: NH4+, Group 1A (except Li+)
Insoluble: Most cations

Question 28

List the cations that form soluble salts and insoluble salts with PO4 3-

Answer 28

Soluble: NH4+, Group 1A (except Li+)
Insoluble: Most cations

Question 29

List the cations that form soluble salts and insoluble salts with thiocyanate SCN-

Answer 29

Soluble: Most cations
Insoluble: Ag+, Hg2 2+, Pb2+