Ch. 20 & 21 notes (acids & bases) teacher

Ch. 20 Notes -- Acids and Bases What makes something an acid?

Acid Properties:

(1) tastes _______-- _______________

(2) corrosive to _________

(3) contains [ ___ ] (or [ _____ ] = “_______________” ions)

(4) proton ([ ___ ]) __________-- Brønsted-Lowry Theory

Example: HCl + H2O ______ + ______

sour lemons

metals

H+ H3O+ hydronium

H+ donor

Cl− H3O+

Examples of Common Acids:

• Pepsi, _________ juices, ___________, stomach acid, battery acid, _____________, ______

citrus aspirinvinegar DNA

Acid Vocabulary• monoprotic acid- contains ____ [H+] ion in its formula

Examples: _______ , ________

• diprotic acid- contains _____ [H+] ions in its formula

Examples: _______ , ________

• triprotic acid- contains _____ [H+] ions in its formula

Examples: _______ , ________

• strong acid - readily ___________ to produce ______ [H+] ions in water

Examples: _________, HNO3, _______

• weak acid - produces a __________ amount of [H+] ions when in water

Examples: HC2H3O2 (vinegar) , _________, _________

1

HCl HNO3

2

H2SO4 H2CO3

3

H3PO4 H3BO3

dissociate many

HCl H2SO4

small

H2CO3 lemon juice

Strong Acids vs. Weak Acids

Indicators• An indicator is a chemical that will change ___________ when

placed in an acidic, basic or neutral environment.

Indicator Colors For Acids

• litmus paper = _______

• phenolphthalein = ___________

• red cabbage juice (universal indicator) = ________

• methyl orange = _______

colors

red

clear

red

red

pH Paper : Indicator Colors

Acidic

Basic

Neutral

Properties of BasesWhat make something a base?

Base Properties: (…the opposite of acid properties)

(1) tastes ________ -- ___________ peel , parsley, dark chocolate

(2) feels _____________ -- ________

(3) contains [ _____ ] ions

(4) proton ([H+]) ______________-- Brønsted-Lowry Theory

Example: NH3 + H2O ______ + _______

bitter banana

slippery soap

OH−

acceptor

NH4+ OH−

Indicator Colors for Bases• litmus paper = _______

• methyl orange = ____________

• red cabbage juice (universal indicator) =________

• phenolphthalein = ______

Acid Base

phenolphthalein

blue

yellow

blue

pink

Common Bases• Examples of Common Bases: milk of magnesia, ___________,

drain cleaner, soap, blood, ____________ tablets, ___________ ________.

ammoniaantacid baking

soda

Strong Bases vs. Weak Bases• strong base- readily __________ to produce ______ [OH−] ions in

water

Examples: NaOH , ________

• weak base- produces a __________ amount of [OH−] ions when in water

Examples: _____ (ammonia); Mg(OH)2 (milk of magnesia)

Other Vocabulary

• _______________- another term for basic solutions

• _______________- a substance that can act as both an acid and a base

Examples: ___________ , ____________

dissociate many

KOH

small

NH3

Alkaline

Amphoteric

H2O HCO3−

Conjugate Acid-Base Pairs

• Conjugate ______- substance formed when a _______ gains a [H+] ion.

• Conjugate ______- substance formed when an ______ loses a [H+] ion.

• Practice Problems: Label the acid & base on the left side of the reaction and the conjugate acid & conjugate base on the right side.

a) HCl + H2O H3O+ + Cl−

______ ______ ______ ______

b) NH3 + H2O NH4+ + OH−

_____ ______ ______ ______

Acid base

Base acid

acid base C.A. C.B.

base acid C.A. C.B.

Self-Ionization of Water• Pure water is _____________. It can ionize itself to form OH− and

H3O+ ions in __________ amounts.

H2O + H2O H3O+ + OH−

(or H2O _______ + _______ )

• The universal indicator color is ___________ in neutral solutions.

neutralsmall

H+ OH−

green

self-ionization of water

Measuring the Amount of H+ and OH− Ions in a Solution

• _____ Scale- measures the _____________ of [H+] ions in a solution

• _____ Scale- measures the concentration of [ ____ ] ions in a solution

Formulas

pH = − (log [H+]) pOH = −(log [OH−])

[H+] = 10−pH [OH−] = 10−pOH

[H+] x [OH−] = 1 x 10−14 pH + pOH = 14

• With the pH scale, we have another way to define acids and bases:

Acids have a pH _________7.0

Bases have a pH _________7.0

Neutral pH ___7.0

pH concentration

pOH OH−

below

above

=

Practice Problems:

1) a) Calculate the pH of a 0.001 M HCl solution

b) What is the pOH of this solution?

c) What is the concentration of [OH−] ions in the solution?

2) a) Calculate the pOH of a NaOH solution that has a pH of 8.50

b) What is the [OH−] of this solution?

c) What is the concentration of [H+] ions in the solution?

[H+] = 0.001 M So…pH = − (log 0.001 M) pH = 3

pH + pOH = 14 So…14 − 3 = pOH pOH = 11

[OH−] = 10−pOH [OH−] = 10−11 Molar or 1 x 10−11 M

So…14 − 8.5 = pOHpH + pOH = 14

[OH−] = 10−5.5 Molar or 3.16 x 10−6 M[OH−] = 10−pOH

[H+] = 10−pH [H+] = 10−8.5 Molar or 3.16 x 10−9 M

pOH = 5.5

Ch. 21 Notes -- NeutralizationNeutralization Reactions

• When an acid and base are mixed, the reaction produces _______ and ___________.

• If the initial concentrations and volumes of the reactants are equal, the products will be ____________... (pH= 7.0)

• All neutralization reactions are ___________ replacement reactions.

HX + M(OH) ______ + ______

saltwater

neutral

double

MX H2O(“Salt”)

Titration• Mixing an acid with a base to

determine a __________________ is called “titration.”

• An ____________ is used to determine when neutralization has occurred.

• ________________ Solution - the solution of known concentration

• ______ _________ - the point of neutralization when titrating

• At the ______ point, the moles of [H+] ions = moles of [OH−] ions.

concentration

indicator

Standard

End Point

end

Practice Problems:

(1) Complete the following neutralization reactions.

HNO3 (aq) + KOH (aq) _________ + __________

HCl (aq) + Ca(OH)2 (aq) __________ + ___________

(2) How many moles of Ca(OH)2 will it take to neutralize 0.5 moles of HCl?

3) How many moles of HNO3 will it take to neutralize 3.0 moles of KOH?

KNO3 H2O

CaCl2 H2O2 2+2 −1

2 moles HCl1 mole Ca(OH)20.5 moles HCl x = 0.25 moles of Ca(OH)2

1 mole KOH1 mole HNO33.0 moles KOH x = 3.0 moles of HNO3

(Macid)x(Vacid) = (Mbase)x(Vbase)

Practice Problems:

(1) A 25 mL solution of HNO3 is neutralized by 18 mL of 1.0 M NaOH standard solution using phenolphthalein as an indicator. What is the concentration of the HNO3 solution?

(2) How many mL of 2.0 M KOH will it take to neutralize 55 mL of a 0.76 M HCl standard solution?

Determining the Concentration of an Acid (or Base) by Titration

( ) x ( ) = ( ) x ( )

( ) x ( ) = ( ) x ( )

Macid 25 mL 1.0 M 18 mL

Macid = 0.72 Molar

0.76 M 55 mL 2.0 M Vbase

Vbase = 20.9 mL