lecture 19.1b- bronsted-lowry acids & bases

Bellwork- concentration review

How many moles of H+ are in 250ml of 3MHCl?

How many moles of OH- are produced when25g of NaOH is dissolved in 250ml ofwater?

What is the molarity of the NaOH solution?

Arrhenius concept

Acids make H+

Bases make OH-

The Brønsted-Lowry definitionof

ACIDS AND BASES

Acids donate protons (H+)HCl H+ + Cl-

Bases accept protons (H+)NH3 + H+ NH4

+

The Bronsted- Lowry model ismore inclusive than the Arrheniusmodel.

NH3 + H+ NH4+

Ammonia is a Bronsted-Lowrybase, but does not dissociate tomake OH-

Why Ammonia is a Base19.1

HA + H2O H3O+ + A-

Acid base conjugate conjugateacid base

An acid donates a proton forming itsconjugate base. HA A-

A base accepts a proton forming itsconjugate acid. NH3 NH4

+

HA A-

Acid conjugate baseA- is ready to accept a proton, it is abase.

NH3 + H+ NH4+

Base conjugate acid

NH4+ has a proton to donate. It is an

acid.

Conjugate Acids and Bases

•A conjugate acid is the particleformed when a base gains ahydrogen ion.

•A conjugate base is the particle thatremains when an acid has donated ahydrogen ion.

19.1

•A conjugate acid-base pairconsists of two substances relatedby the loss or gain of a singleproton.

•A substance that can act as bothan acid and a base is said to beamphoteric.

Water is amphoteric.Water can be an acid or a base

H2O H+ + OH-

Water can ionize and donate aproton.

H2O H3O+

As a base, water accepts a protonforming the hydronium ion.

A conjugate acid-base pair consists oftwo substances related to each other bythe donating and accepting of a proton

Are the following pairs conjugate acid-base pairs?

a. H2O H3O+

b. OH- HNO3

c. HC2H3O2 C2H3O2-

Brønsted-Lowry Acidsand Bases

19.1

Identify conjugate acid base pairs

HCl + NH3 NH4+ + Cl-

HSO4- + OH- H2O + SO42-

NH3 + H2O NH4+ + OH-

Lewis Acids and Bases

Lewis definition

an acid accepts a pair of electrons

a base donates a pair of electrons.

Lewis Acids and Bases

•A Lewis acid is a substance that canaccept a pair of electrons to form acovalent bond.

•A Lewis base is a substance that candonate a pair of electrons to form acovalent bond.

19.1

Animation 25 Compare the three importantdefinitions of acids and bases.

Lewis Acids and Bases19.1

1. Which of the following is NOT acharacteristic of acids?

a. taste sour

b. are electrolytes

c. feel slippery

d. affect the color of indicators

19.1 Section Quiz.

2. Which compound is most likely toact as an Arrhenius acid?

a. H2O

b. NH3.

c. NaOH.

d. H2SO4.

19.1 Section Quiz.

3. A Lewis acid is any substance thatcan accept

a. a hydronium ion.

b. a proton.

c. hydrogen.

d. a pair of electrons.

19.1 Section Quiz.

pHThe pH scale measures thehydrogen ion

concentration[H+] of asolution.

A pH of 7 is neutral

A pH less than 7 is acidic (litmus red)

A pH greater than 7 is basic (litmusblue)

The pH scale ranges from below zero (veryacidic) to above14 (very basic)

The pH scale is not linear.

The pH scale is logarithmic.

pH = -log[H+]

[H+] = 1.0 x 10-2 pH = 2 very acidic

[H+] = 1.0 x 10-3 pH = 3 acidic

A solution with pH of 2 contains 10 timesas much H+ as a solution with pH of 3.

Acidic = more H+ than OH-

Basic = more OH- than H+

From pH 0 to pH 14 theH+ concentration decreases100,000,000,000,000 times!!

Measuring pH

An indicator is a valuable toolfor measuring pH because itis a different color in acidicsolution than when in base.

19.2

Measuring pH

Phenolphthaleinchanges fromcolorless topink at pH7–9.

19.2

Measuring pH19.2

Measuring pH

Universal Indicators

19.2

Measuring pH

– pH Meters

19.2

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Solu%on RedLitmus

BlueLitmus

pHpaper Universalindicator

Acid,Base,orneutral?

lemonjuice(diluted)

bakingsoda+H2O

Drano(NaOH)(diluted)

Lysol(diluted)

Vinegar