Chemistry 5.9Chemistry 5.9

Oxidation-ReductionOxidation-Reduction

Oxidation- Oxidation- Loss of electrons by an atom or ionLoss of electrons by an atom or ion..

Reduction-Reduction- Gain of electrons by an atom or ionGain of electrons by an atom or ion..

Neither reduction or oxidation can Neither reduction or oxidation can take place alone. take place alone.

LEOLEO the lion says the lion says GERGER!!

+1 or 1+?+1 or 1+?

The charge of a sodium ion is +1The charge of a sodium ion is +1

The oxidation number of sodium The oxidation number of sodium in NaCl is 1+.in NaCl is 1+.

Don’t sweat this, it’s not a big Don’t sweat this, it’s not a big deal!deal!

Ok, some rules of Ok, some rules of Redox:Redox:

1.1. Any element in pure form has an Any element in pure form has an oxidation state of ‘zero’ (0).oxidation state of ‘zero’ (0).

2.2. Hydrogen has an oxidation number of Hydrogen has an oxidation number of +1 (HCl) when combined with a non-+1 (HCl) when combined with a non-metal, and -1 when combined with a metal, and -1 when combined with a metal (NaH).metal (NaH).

3.3. Oxygen has a charge of -2 in Oxygen has a charge of -2 in compounds except when combined compounds except when combined with fluorine or in peroxide. with fluorine or in peroxide.

……more rulesmore rules

The sum of the oxidation numbers The sum of the oxidation numbers in all compounds must be zero.in all compounds must be zero.

The sum of the oxidation numbers The sum of the oxidation numbers in polyatomic ions must be equal in polyatomic ions must be equal to the charge on the ion.to the charge on the ion.

To be, or not to be…To be, or not to be…Redox.Redox.

If there is a change in oxidation If there is a change in oxidation numbers for any atom in a numbers for any atom in a reaction, then redox must take reaction, then redox must take place.place.

Double displacement rxs are not Double displacement rxs are not redox.redox.

Oxidizing and reducing Oxidizing and reducing agents.agents. The substance being oxidized is The substance being oxidized is

the reducing agent.the reducing agent. The substance being reduced is The substance being reduced is

the oxidizing agent.the oxidizing agent.

Half reactionsHalf reactions

A half reaction shows either the A half reaction shows either the reduction or oxidation portion of a reduction or oxidation portion of a given redox reaction.given redox reaction.

Remember your laws of Remember your laws of conservation!conservation!

Electrochemical CellsElectrochemical Cells

1.1. Galvanic (Voltaic) Cell-Galvanic (Voltaic) Cell- A chemical reaction is used to produce a flow A chemical reaction is used to produce a flow

of electrons (batteries).of electrons (batteries). Requires a salt bridge to complete the circuit.Requires a salt bridge to complete the circuit.

2.2. Electrolytic cell-Electrolytic cell- An electric current is used to force a chemical An electric current is used to force a chemical

reaction (metal plating).reaction (metal plating).

3.3. Red cat, an oxRed cat, an ox.:.: Reduction takes place at the cathode, and Reduction takes place at the cathode, and

oxidation takes place at the anode. Always.oxidation takes place at the anode. Always.

The Voltaic CellThe Voltaic Cell

The half reactions of The half reactions of the Voltaic cellthe Voltaic cell

1.1. Zn Zn2+ + 2e-      0.76vZn Zn2+ + 2e-      0.76v

2.2. Cu2+ + 2e- Cu     +0.34vCu2+ + 2e- Cu     +0.34v__________________________________________________Zn + Cu2+ Zn2+ + Cu    1.10vZn + Cu2+ Zn2+ + Cu    1.10v

Look at table J the activity series.Look at table J the activity series. Remember the money metals do Remember the money metals do

not easily oxidize (except Nickel. not easily oxidize (except Nickel. Why?)Why?)

Electrolytic CellsElectrolytic Cells

The action of The action of electrolysis in an electrolysis in an electrolytic cell:electrolytic cell:

1.1. In the aqueous solution copper In the aqueous solution copper sulphate dissociates into its sulphate dissociates into its respective ions.respective ions.

2.2. On passing electric current the On passing electric current the copper ions (cations) move towards copper ions (cations) move towards the cathode and get deposited as the cathode and get deposited as copper. Simultaneously the sulphate copper. Simultaneously the sulphate ions (anions) move towards the ions (anions) move towards the anode.anode.

Acids and BasesAcids and Bases

An Arrhenius acid is one that An Arrhenius acid is one that produces Hydrogen (H+) or produces Hydrogen (H+) or Hydronium (HHydronium (H33O+) ions in O+) ions in solution. solution.

An Arrhenius base is one that An Arrhenius base is one that produces Hydroxide (OH-) ions in produces Hydroxide (OH-) ions in solution. solution.

HCl + NaOHHCl + NaOH

HCl HCl →→ H+ H+(aq) (aq) + Cl-+ Cl-(aq)(aq)

NaOH NaOH → → Na+Na+(aq)(aq) + OH- + OH-(aq)(aq)

Neutralization reaction:Neutralization reaction:HCl + NaOH HCl + NaOH → NaCl + H→ NaCl + H22OO

Naming Acids & BasesNaming Acids & Bases

Binary acids begin with Binary acids begin with hydro hydro and and end with the end with the icic ending. Ex/ ending. Ex/ hydrohydrochlorchloricic acid (HCl) acid (HCl)

Bases use the true name of the Bases use the true name of the positive ion with positive ion with hydroxidehydroxide ending. Ex/ ending. Ex/ calcium hydroxide calcium hydroxide [Ca(OH)[Ca(OH)22].].

Reactions with Acids Reactions with Acids and Metalsand Metals

If the metal is higher than HIf the metal is higher than H22 on on the activity series table, than it the activity series table, than it will react with the acid (H+) to will react with the acid (H+) to produce Hproduce H22 and a salt. and a salt.

ZnZn(s)(s) + HCl + HCl(aq)(aq) → H→ H2(g)2(g) + ZnCl + ZnCl2(aq)2(aq)

TitrationTitration

Titration is a procedure used in Titration is a procedure used in chemistry in order to determine chemistry in order to determine the the molaritymolarity of an of an acidacid or a or a basebase. . A chemical reaction is set up A chemical reaction is set up between a known volume of a between a known volume of a solution of solution of unknown concentrationunknown concentration and a and a known volume of a solution known volume of a solution with a known concentration. with a known concentration.

Solving Titration Solving Titration Problems:Problems:

Use the formula:Use the formula: MM11VV1 1 =M=M22VV22

Find the molarity of a HCl solution Find the molarity of a HCl solution if 50.0 ml of a 0.250 M KOH are if 50.0 ml of a 0.250 M KOH are needed to neutralize 20.0 ml of needed to neutralize 20.0 ml of HCL.HCL.

The pH scaleThe pH scale

Measures the negative log of the Measures the negative log of the hydronium concentration [H+] or hydronium concentration [H+] or [H[H33O].O].

Measured between 0 and 14. Measured between 0 and 14.

Acid-Base indicatorsAcid-Base indicators

Each indicator will change color Each indicator will change color when the solution falls within a when the solution falls within a certain certain pH range. pH range.

Common indicators are Common indicators are phenolphthalein and methyl phenolphthalein and methyl orange.orange.

Conjugate Acid-Base Conjugate Acid-Base pairs.pairs.

When an acid gives up its proton, what When an acid gives up its proton, what remains is called the conjugate base of remains is called the conjugate base of that acid. When a base accepts a that acid. When a base accepts a proton, the resulting chemical is called proton, the resulting chemical is called the conjugate acid of that original the conjugate acid of that original base. HF and F- are a conjugate acid-base. HF and F- are a conjugate acid-base pair. H2O and H3O+ are a base pair. H2O and H3O+ are a conjugate pair, where H3O+ is the acid conjugate pair, where H3O+ is the acid and H2O is the base.and H2O is the base.