4.8 acid-base reactions

4.8 Acid-Base 4.8 Acid-Base ReactionsReactions

DefinitionsDefinitions

Arrhenius:Arrhenius: Acid- produces HAcid- produces H++ when dissolved in water when dissolved in water Base- produces OHBase- produces OH-- when dissolved in water when dissolved in water

Bronsted-LowryBronsted-Lowry:: AcidAcid- H- H++/proton donor/proton donor BaseBase- H- H++/proton acceptor/proton acceptor

Since HSince H22O is a non-electrolyte, large O is a non-electrolyte, large amounts of OHamounts of OH-- and H and H++ cannot exist in cannot exist in solution without combiningsolution without combining

Lewis ModelLewis Model

even more general than Bronsted-even more general than Bronsted-Lowry Lowry

acidacid electron pair acceptorelectron pair acceptor has empty atomic orbitalshas empty atomic orbitals

basebase electron pair donorelectron pair donor has lone pairhas lone pair

HA ----> H3O+ + A-

ArrheniusAcidH2O

O

HH

HA

O

HHH

+

+ A-

Lewis BaseLewis Base

Monoprotic acid: HClMonoprotic acid: HCl

HClHCl(aq) (aq) + NaOH+ NaOH(aq) (aq) ---> --->

HH22OO(l) (l) + NaCl+ NaCl(aq)(aq)

HH++ + Cl + Cl-- + Na + Na++ + OH + OH-- ---> --->

HH22O + NaO + Na++ + Cl + Cl--

HH++ + OH + OH-- ---> H ---> H22OO

Diprotic acid: HDiprotic acid: H22SOSO44

Polyprotic acid: HPolyprotic acid: H33POPO44

Strong AcidsStrong Acids

Know these!!!Know these!!!

1.1. HCl – hydrochloric acidHCl – hydrochloric acid2.2. HBr – hydrobromic acidHBr – hydrobromic acid3.3. HI – hydroiodic acidHI – hydroiodic acid

4.4. HH22SOSO4 4 – sulfuric acid– sulfuric acid

5.5. HNOHNO3 3 – nitric acid– nitric acid

6.6. HClOHClO4 4 – perchloric acid– perchloric acid

Strong BasesStrong Bases

All are metal hydroxides – especially All are metal hydroxides – especially group I and II group I and II Dissociate completely in waterDissociate completely in water List List

Neutralization ReactionsNeutralization Reactions

Metathesis reaction Metathesis reaction AKA Double AKA Double replacement or displacement replacement or displacement

Typically involves ion transfer (not Typically involves ion transfer (not redox)redox)

Involves reaction of HInvolves reaction of H++ (or H (or H33OO++) and ) and OHOH- - to form water moleculesto form water molecules

Arrhenius acid/base Arrhenius acid/base

reactionreaction

NeutralizationNeutralization

acid + base ---> Hacid + base ---> H22O + a saltO + a salt

HA + MOH ---> HHA + MOH ---> H22O + MAO + MA

Salt = ionic compound formed Salt = ionic compound formed from the anion of an acid and the from the anion of an acid and the cation from a basecation from a base

NeutralizationNeutralizationExample 4.13 p. 160Example 4.13 p. 160

28.0 mL of 0.250 M HNO28.0 mL of 0.250 M HNO33 is is added to 53.0 mL of 0.320 M added to 53.0 mL of 0.320 M KOH. Calculate the grams of KOH. Calculate the grams of water formed. What is the water formed. What is the concentration of Hconcentration of H++ and OH and OH-- ions ions after reaction is complete?after reaction is complete?

Example 1Example 1

Write balanced net ionic equation.Write balanced net ionic equation.Molecular:Molecular:

HNOHNO33(aq) + KOH(aq) (aq) + KOH(aq) H H22O(l) + KNOO(l) + KNO33(aq)(aq)

Complete Ionic:Complete Ionic:

HH++(aq) + NO(aq) + NO33--(aq) + K(aq) + K++(aq) + OH(aq) + OH--(aq) (aq)

HH22O(l) + KO(l) + K++(aq) + NO(aq) + NO33--(aq)(aq)

Net Ionic:Net Ionic:

HH++(aq) + OH(aq) + OH--(aq) (aq) H H22O(l)O(l)

Example 1Example 1

Find number of moles of each reactantFind number of moles of each reactant

HH++::

OHOH--::

molHmolHNO

molH

L

molHNO 3

3

3 1000.71

1

1

250.0L 0.0280

molOHmolKOH

molOH

LKOH

molKOHLKOH 21070.1

1

1

1

320.00530.0

Example 1Example 1

Find limiting reactantFind limiting reactant

Since we have extra OHSince we have extra OH-- left, H left, H++ is the LR. is the LR.

Find the grams of product made.Find the grams of product made.

neededmolOHmolH

molOHmolH

33 1000.7

1

11000.7

OgHOmolH

OgH

molH

OmolHmolH 2

2

223 126.01

02.18

1

11000.7

Example 1Example 1

Find the concentrations of HFind the concentrations of H++ and OH and OH--

Since H+ was the limiting reactant, there Since H+ was the limiting reactant, there should be none left.should be none left.

We already calculated how much OH- will be We already calculated how much OH- will be used, so to find the amount left, we can used, so to find the amount left, we can subtract.subtract.

To find the molarity, divide the moles by total To find the molarity, divide the moles by total volume:volume:

0H

molOH0100.000700.00170.0

MOHLL

molOHOH 123.0

0530.00280.0

0100.0

TitrationsTitrations volumetric analysis-volumetric analysis- technique technique

used to find amount of certain used to find amount of certain substance by doing a titrationsubstance by doing a titration

titrationtitration- when you add a - when you add a certain volume of a solution certain volume of a solution with a known concentration with a known concentration ((titranttitrant) to a certain amount of ) to a certain amount of solution being analyzed solution being analyzed ((analyteanalyte))

TitrationsTitrations

equivalence point-equivalence point- when there are when there are equal moles of each reactant presentequal moles of each reactant present

indicatorindicator- substance that changes - substance that changes color near equivalence pointcolor near equivalence point

end point-end point- when indicator changes when indicator changes colorcolor

TitrationsTitrations

For a good titration:For a good titration: reaction between titrant and analyte must be reaction between titrant and analyte must be

knownknown equivalence point must be marked accuratelyequivalence point must be marked accurately volume of titrant needed for equivalence must volume of titrant needed for equivalence must

be knownbe known phenolphthalein- phenolphthalein-

common indicator used common indicator used clear until acid is consumed and one drop of clear until acid is consumed and one drop of

excess base is added; turns pinkexcess base is added; turns pink

Neutralization Titration - Neutralization Titration - Example 4.14 p. 162 - 163Example 4.14 p. 162 - 163

To standardize a sodium hydroxide To standardize a sodium hydroxide solution, a student plans to titrate the solution, a student plans to titrate the solution with a monoprotic acid, KHP solution with a monoprotic acid, KHP (KHC(KHC88HH44OO44, potassium hydrogen , potassium hydrogen phthalate). She dissolves 1.3009 g of KHP phthalate). She dissolves 1.3009 g of KHP in water, adds phenolphthalein, and in water, adds phenolphthalein, and titrates to the endpoint. It took 41.20 mL titrates to the endpoint. It took 41.20 mL of sodium hydroxide to titrate the KHP of sodium hydroxide to titrate the KHP solution. solution.

Calculate the concentration of NaOH.Calculate the concentration of NaOH.

Example 2Example 2

Write the balanced net ionic equation:Write the balanced net ionic equation:

NaOH(aq) + KHP(aq) NaOH(aq) + KHP(aq) NaKP(aq) + H NaKP(aq) + H22O(l)O(l)

NaNa++(aq) + OH(aq) + OH--(aq) + KHP(aq) (aq) + KHP(aq) NaNa++(aq) + KP(aq) + KP--(aq) + H(aq) + H22O(l)O(l)

OHOH--(aq) + KHP(aq) (aq) + KHP(aq) H H22O(l) + KPO(l) + KP--(aq)(aq)

Example 2Example 2

Find the moles of HFind the moles of H++ in the KHP: in the KHP:

Find the moles of NaOH used:Find the moles of NaOH used:

Find molarity of NaOH used:Find molarity of NaOH used:

molHmolKHP

molH

gKHP

molKHPgKHP 0063701.0

1

1

22.204

13009.1

molNaOHmolOH

molNaOH

molH

molOHmolH 0063701.0

1

1

1

10063701.0

MNaOHL

molNaOHNaOH 1546.0

04120.0

0063701.0

Neutralization Analysis Neutralization Analysis Example 4.15 p. 163 – 164 Example 4.15 p. 163 – 164

A 0.3518 g mixture of CClA 0.3518 g mixture of CCl44 and and HCHC77HH55OO22 was mixed with water was mixed with water and titrated by 10.59 mL of and titrated by 10.59 mL of 0.1546 M NaOH. 0.1546 M NaOH.

Find the percent by mass of Find the percent by mass of HCHC77HH55OO22 in the original sample. in the original sample.

Example 3Example 3

Write the net ionic equationWrite the net ionic equation

HCHC77HH55OO22(aq) + OH(aq) + OH--(aq) (aq)

HH22O(l) + CO(l) + C77HH55OO22--(aq)(aq)

Find moles of OH- used:Find moles of OH- used:

molOHmolNaOH

molOH

L

molNaOHL 001637.0

1

1

1

1546.001059.0

Example 3Example 3

Find moles of HCFind moles of HC77HH55OO22 used: used:

Find the grams of HCFind the grams of HC77HH55OO22::

Find percent by mass:Find percent by mass:

257257 001637.0

1

1

1

1001637.0 OHmolHC

molH

OHmolHC

molOH

molHmolOH

257257

257257 1999.0

1

2.122001637.0 OHgHC

OHmolHC

OHgHCOHmolHC

257257 %83.56

3518.0

1999.0% OHHC

gtotal

OHgHC