CHAPTER 4CHAPTER 4

AP CHEMISTRYAP CHEMISTRY

PRECIPITATION PRECIPITATION PROBLEMSPROBLEMSWaterWater

Highly polarHighly polarIonic and polar compounds are attracted to the positive Ionic and polar compounds are attracted to the positive and/or negative ends of the water molecule. This is and/or negative ends of the water molecule. This is called HYDRATION (a hydration reaction is something called HYDRATION (a hydration reaction is something different)different)

When a precipitate is formed there is a zero net chargeWhen a precipitate is formed there is a zero net chargeSolubility rules (handout)Solubility rules (handout)What happens when a ionic compound dissolves in water?What happens when a ionic compound dissolves in water?

They break up into their ion formThey break up into their ion formWhat are spectator ions?What are spectator ions?

Ions that do not participate in the reactionIons that do not participate in the reactionYou must show that atoms and charges are balanced You must show that atoms and charges are balanced

ELECTROYTESELECTROYTES Solute - substanceSolute - substance Solvent - water, what you put solute inSolvent - water, what you put solute in Electrolytes- conduct electricityElectrolytes- conduct electricity

Strong - strong acids and bases, soluble saltsStrong - strong acids and bases, soluble salts Weak - weak acids and bases, insoluble or slightly Weak - weak acids and bases, insoluble or slightly

soluble saltssoluble salts Nonelectroytes - molecules, nonpolar covalent Nonelectroytes - molecules, nonpolar covalent

compoundscompounds ARRHENIUSARRHENIUS

Ions are responsible for conducting electricityIons are responsible for conducting electricity Down played convictions to get PhD then crusaded Down played convictions to get PhD then crusaded

to get theory acceptedto get theory accepted Received Nobel prize 1903Received Nobel prize 1903

OXIDATION-REDUCTION OXIDATION-REDUCTION REACTIONSREACTIONS

An oxidation-reduction reaction involves transfer of electronsAn oxidation-reduction reaction involves transfer of electrons Addition of OAddition of O22 or H or H2 2 often occuroften occur LEO goes GER LEO goes GER Oxidized or oxidationOxidized or oxidation

Species that lose electronsSpecies that lose electrons oxidation number goes upoxidation number goes up

Reduced or reductionReduced or reduction Species that gain electrons or oxidation number reducedSpecies that gain electrons or oxidation number reduced

Oxidizing agentOxidizing agent What causes oxidationWhat causes oxidation

Reducing agentReducing agent What causes reductionWhat causes reduction

OXIDATION NUMBER OXIDATION NUMBER RULESRULES Elements found in nature is zeroElements found in nature is zero Cu, OCu, O22

Monoatomic ions same as chargeMonoatomic ions same as charge ClCl--, Mg, Mg2+2+

Fluorine always 1-Fluorine always 1- Oxygen 2-Oxygen 2-

Except with fluorine 2+Except with fluorine 2+ Peroxide 1-, HPeroxide 1-, H22OO22

Superoxide ½ -, KOSuperoxide ½ -, KO22

Hydrogen 1+Hydrogen 1+ With group one elements then a hyride 1-With group one elements then a hyride 1-

Sum of oxidation numbers of a neutral compound is zeroSum of oxidation numbers of a neutral compound is zero The most electronegative element number is the same as the ion chargeThe most electronegative element number is the same as the ion charge Sum of oxidation numbers of a polyatomic ion is same as its chargeSum of oxidation numbers of a polyatomic ion is same as its charge

REDOXREDOX The concept of oxidation numbers explain oxidation and The concept of oxidation numbers explain oxidation and

reductionreduction Oxidation: increase in oxidation number (lose electrons)Oxidation: increase in oxidation number (lose electrons) Reduction: decreases in oxidation number (gain electrons)Reduction: decreases in oxidation number (gain electrons) Balancing redox equationsBalancing redox equations

The half-equation methodThe half-equation method Split the equation into two half-reactionsSplit the equation into two half-reactions One for reduction and the other for oxidationOne for reduction and the other for oxidation Balance one of the half-reactions; balance atom other than O or H Balance one of the half-reactions; balance atom other than O or H

first, next use water to balance oxygen, then add hydrogen ions to first, next use water to balance oxygen, then add hydrogen ions to balance the hydrogen, add electrons to balance chargebalance the hydrogen, add electrons to balance charge

Balance other half-reactionBalance other half-reaction Combine the two in such away as to eliminate all the electronsCombine the two in such away as to eliminate all the electrons

MOLARITTYMOLARITTY

Number of moles of solute per liter of Number of moles of solute per liter of solutionsolution

M = number of mol/LM = number of mol/L Symbol [ ] means molar concentrationSymbol [ ] means molar concentration Moles of solute after dilution = moles of Moles of solute after dilution = moles of

solute before dilutionsolute before dilution MM11VV11 = M = M22VV22

TITRATIONTITRATION A volumetric analysis involving titration, where a A volumetric analysis involving titration, where a

measured volume of a known concentration of an measured volume of a known concentration of an acid or base is required to find the exact acid or base is required to find the exact concentration (concentration (the volume must be knownthe volume must be known) of an ) of an unknown base or acidunknown base or acid

Equivalent pointEquivalent point Where exact stoichometry amounts of each Where exact stoichometry amounts of each

reactant are present. (same number of Hreactant are present. (same number of H++ and and OHOH- - ) NO EXCESSES) NO EXCESSES

End pointEnd point Where the indicator changes color. Immediately Where the indicator changes color. Immediately

stop adding titrate.stop adding titrate.