Studying Oxidation-Reduction Reactions

an electron transfer reaction is called what?

oxidation-reduction or redox

oxidized

one reactant loses electrons

reduced

one reactant gains electrons

How is the green chromium (III) ion produced in a Breathalyzer?

the orange solution of dichromate ion (Cr2O7) reacts with ethanol fumes (CH3CH2OH)

What does propane react with and what does it produce?

it reacts with atmospheric oxygen and produces carbon dioxide, water, and heat.

the number of electrons released in any oxidation half-reaction must exactly equal what?

the number of electrons consumed in the corresponding half reaction

what serves as an electron source for Cl2?

Ca

what is Ca referred to in this lab?

the reducing agent

what is Cl2 referred to as?

the oxidizing agent

in equation 1, what accepts the electrons from carbon atoms in C3H8?

O2

in equation 2, where are the electrons in CH3CH2OH transferred to?

Cr2O7

what is each carbon atom in the CO2 is combined with what?

two oxygen atoms and no hydrogen

Explain how oxidation and reduction is happening in equation 1?

* the carbon in propane decreases in hydrogen content and increases in oxygen content, forming CO2; therefor oxidized
* some of the oxygen gains hydrogen during the process, forming water; therefore reduced

Explain how oxidation and reduction is happening in equation 2?

* the chromium atoms in Cr2O7 2- ion are combined with oxygen, but in Cr3+ ion, chromium is no longer combined with oxygen; therefor Cr2O7 ion is reduced
* the hydrogen content per carbon atom decreases, so CH3CH2OH is oxidized

depending on the chemical environment, copper can exists as what?

* elemental Cu
* copper (I) ion
* copper (II) ion

what happens to copper in the presence of a oxidizing agent stronger than Cu+?

red-brown Cu is oxidized to Cu2+ ion

what happens to Cu when O2 is the oxidizing agent?

a solid black copper (II) oxide (CuO) forms

how do we know there is Cu2+ present in CuO?

by dissolving some of the solid in acidic solution and testing for Cu2+ ion

what color is Cu2+ in an aqueous solution?

aqua blue

what color is is Cu2+ in an ammonia solution (NH3)?

deep blue

What ion is made when Cu2+ is put in an ammonia solution?

\[Cu(NH3)6\]2+

what metals can reduce Cu2+ to Cu?

Zn or Fe

what is a good Cu2+ source?

Copper (II) sulfate

(CuSO4)

is copper (II) sulfate water soluble?

yes

Benedict’s reagent

where Cu2+ ion is complexed with citrate ion to prevent precipitation of copper (II) hydroxide, Cu(OH)2

what happens if glucose is present in Benedicts reagent?

if glucose is present in the body fluid being tested, it reduces Cu2+ ion to Cu+ ion, which precipitates as red copper (I) oxide (Cu2O) from the basic solution.

if glucose is present in Benedicts reagent, what does Cu2+ transform into?

the blue Cu2+ turns into red Cu2O

what are the three common oxidation states of iron?

* Fe
* Fe2+ ion
* iron (III) ion

what form of iron do we associate with rust?

Fe2O3

although O2 oxidized Fe2+ to Fe3+, what is a faster way we can observe this?

by using hydrogen peroxide (H2O2)

the effectiveness of H2O2 as an antiseptic is based on its ability to do what?

oxidize bacterial membranes, resulting in the destruction of the cell.

what is magnesiums town oxidation states?

* Mg
* Mg2+

what type of agent is magnesium?

reducing agent

what does magnesium as a strong reducing agent do?

releases two valence electrons to assume a noble gas electron configuration

what doe we see when Mg reacts with O2?

large amount of energy is produced in the form of light

what doe we see when Mg reacts with H+ ion?

flammable molecular hydrogen, H2

what is paper mainly composed of?

cellulose, a polymer of glucose molecule units

what is cellulose’ chemical formula?

(C6H12O6)n

what does “n” represent on cellulose?

number of glucose units

what is cellulose oxidized by?

atmospheric O2

how many valence electrons do halogens have?

7

what is the strongest oxidizing agent?

fluorine

Are halogens soluble?

no, but they are soluble in non polar solvents

what is cyclohexane (C6H12) describes as?

a non polar solvent

what happens to bromine and iodine when dissolved in C6H12?

Br2 turns to a red-brown and I2 turns into a violet

how can we test the relative oxidizing strengths of Br2 and I2?

we can mix a small volume of Br2 in C6H12 with a small volume of colorless aqueous potassium iodide solution (KI)

what will we see if Br2 is a stronger oxidizing agent than I2?

electrons will be transferred from I- ion to bromine atoms, resulting in the formation of bromide ions (Br-) and I2.

proof of this reaction would be the color change in the reaction solution from brown to violet, indicating that the presence of dissolved I2.