Acids and Bases IIAcids and Bases II

Dr. Ron RusayDr. Ron Rusay

Summer 2004Summer 2004

© Copyright 2004 R.J. Rusay© Copyright 2004 R.J. Rusay

Water as an Acid and a BaseWater as an Acid and a Base

Amphoteric substancesAmphoteric substances can act as can act as either an acid or a baseeither an acid or a base

• Water acting as an acid:Water acting as an acid: ___+ H___+ H22OO ___ + OH ___ + OH-1-1

• Water acting as a base:Water acting as a base: HCl + HHCl + H22O O _____ + ____ _____ + ____

• Water reacting with itself as both:Water reacting with itself as both:

HH22O + HO + H22OO _____ + ____ _____ + ____

Water as an Acid and a BaseWater as an Acid and a Base

Water is Water is amphoteric.amphoteric. It can behave either as It can behave either as an acid or a base.an acid or a base.

HH22OO(l)(l) + H + H22OO(l)(l) H H33OO++(aq)(aq) + OH + OH

(aq)(aq)

acid 1 base 1acid 1 base 1 The equilibrium expression for pure water The equilibrium expression for pure water is:is:

KKww = =

Water: Self-ionizationWater: Self-ionization

Autoionization of WaterAutoionization of Water

Water is an extremely weak electrolyte Water is an extremely weak electrolyte therefore are only a few ions present:therefore are only a few ions present:

KKww = [H = [H33OO+1+1] [OH] [OH-1-1] = _________ @ 25°C] = _________ @ 25°C

• NOTE: the concentration of HNOTE: the concentration of H33OO+1+1 and OH and OH-1-1 are are

equalequal

• [H[H33OO+1+1] = [OH] = [OH-1-1] = ______ @ 25°C] = ______ @ 25°C

• KKww is called the is called the ion product constantion product constant for water: for water:

as [Has [H33OO+1+1] increases, [OH] increases, [OH--] ________ and vice ] ________ and vice

versa.versa.

Acidic and Basic SolutionsAcidic and Basic Solutions

AcidicAcidic solutions have: solutions have: a larger ____ than ____a larger ____ than ____

BasicBasic solutions have: solutions have: a larger ____ than ____a larger ____ than ____

Neutral Neutral solutions have solutions have [H[H+1+1] = [OH] = [OH-1-1] = _______] = _______ MM

[H+1] = 1 x 10-14

[OH-1][OH-1] = 1 x 10-14

[H+1]

The pH ScaleThe pH Scale pH pH log [Hlog [H++] ] log [Hlog [H33OO++] ]

1 pH unit corresponds to a factor of 101 pH unit corresponds to a factor of 10 pH in water ranges from __ to __.pH in water ranges from __ to __.

KKww = _____________ = [H = _____________ = [H++] [OH] [OH]]

-log K-log Kww = -log [H = -log [H33OO+1+1] -log [OH] -log [OH-1-1] ]

pKpKww = pH + pOH = pH + pOH = = _______ _______ As pH rises, pOH falls (Sum = _____).As pH rises, pOH falls (Sum = _____).

pH & pOHpH & pOH

pH = -log[HpH = -log[H33OO+1+1]]pOH = -log[OHpOH = -log[OH-1-1]]• pHpHwaterwater = -log[10 = -log[10-7-7] = 7 = pOH] = 7 = pOHwaterwater

[H[H33OO+1+1] = 10 ] = 10 -pH-pH [OH[OH-1-1] = 10 ] = 10 -pOH-pOH

pH < 7 is ______; pH > 7 is _____, pH = 7 is pH < 7 is ______; pH > 7 is _____, pH = 7 is ________________

The lower the pH, the more _______ the The lower the pH, the more _______ the solution; The higher the pH, the more _____ solution; The higher the pH, the more _____ the solutionthe solution

pOH = 14 - pHpOH = 14 - pH

There are no theoretical limits on the values of pH or pOH. (e.g. pH of 2.0 M HCl is -0.301, the pH at Iron Mountain, California is ~ -2 to -3)

What’s in these household products?What’s in these household products?Acids or bases?Acids or bases?Strong or weak? Strong or weak?

Should you be concerned about safety?Should you be concerned about safety?

The pH of Some Familiar

Aqueous Solutions

[H3O+]

[OH-]

[OH-] = KW

[H3O+]

_______solution

_______solution

_______solution

[H3O+]> [OH-]

[H3O+]< [OH-]

[H3O+] = [OH-]What’s your diet?What’s your diet?

Your urine will tell!Your urine will tell!

Example #1Example #1

Determine the given information and Determine the given information and the information you need to findthe information you need to find

Given [HGiven [H+1+1] = ____ M] = ____ M Find [OHFind [OH-1-1]] Solve the Equation for the Unknown Solve the Equation for the Unknown

AmountAmount

][H

K ]OH[

][OHx ][H K

1w1-

1-1w

+

+

=

=

Determine the [H+1] and [OH-1] in a 10.0 M H+1 solution

Convert all the information to Scientific Convert all the information to Scientific Notation and Plug the given Notation and Plug the given information into the equation.information into the equation.

Given [HGiven [H+1+1] = 10.0 M] = 10.0 M = 1.00 x 10= 1.00 x 1011 M M

KKww = 1.0 x 10 = 1.0 x 10-14-14

M 10x 1.0 10x 1.00

10x 1.0 ]OH[

][H

K ]OH[

15-1

14-1-

1w1-

==

= +

Example #1 (continued)Example #1 (continued)Determine the [H+1] and [OH-1] in a

10.0 M H+1 solution

Example #2Example #2

Find the concentration of [HFind the concentration of [H+1+1]]

M 10x 1.0 10x 1.0

10x 1.0 ]H[

][OH

K ]H[

8-6-

14-1

1w1

==

=

+

−+

Calculate the pH of a solution with a [OH-1] = 1.0 x 10-6 M

Enter the [HEnter the [H+1+1] concentration into your ] concentration into your calculator and press the calculator and press the loglog key key

log(1.0 x 10log(1.0 x 10-8-8) = ____) = ____ Change the sign to get the pHChange the sign to get the pH

pH = -(-8.0) = ____pH = -(-8.0) = ____

Example #2 continuedExample #2 continued

Calculate the pH of a solution with a [OH-1] = 1.0 x 10-6 M

Enter the [HEnter the [H+1+1] or [OH] or [OH-1-1]concentration into ]concentration into your calculator and press the your calculator and press the loglog key key

log(1.0 x 10log(1.0 x 10-3-3) = ___) = ___ Change the sign to get the pH or pHChange the sign to get the pH or pH

pOH = ______pOH = ______ Subtract the calculated pH or pOH from Subtract the calculated pH or pOH from

14.00 to get the other value14.00 to get the other valuepH = _____ – ____ = ____pH = _____ – ____ = ____

Calculate the pH and pOH of a solution with a [OH-1] = 1.0 x 10-3 M

Example #3Example #3

If you want to calculate [OHIf you want to calculate [OH-1-1] use pOH, if you ] use pOH, if you want [Hwant [H+1+1] use pH. It may be necessary to ] use pH. It may be necessary to convert one to the other using 14 = [Hconvert one to the other using 14 = [H+1+1] + [OH] + [OH--

11]]pOH = ______ – ____ = _____pOH = ______ – ____ = _____

Enter the pH or pOH concentration into your Enter the pH or pOH concentration into your calculatorcalculator

Change the sign of the pH or pOHChange the sign of the pH or pOH-pOH = ______-pOH = ______

Press the button(s) on you calculator to take Press the button(s) on you calculator to take the inverse log or 10 the inverse log or 10 xx

[OH[OH-1-1] = 10 ] = 10 -6.59-6.59 = ______ = ______

Example #4Calculate the [OH-1] of a solution with a pH of 7.41

Calculating the pH of a Strong, Calculating the pH of a Strong, Monoprotic AcidMonoprotic Acid

A strong acid will dissociate 100%A strong acid will dissociate 100%

HA HA H H+1+1 + A + A-1-1

Therefore the molarity of HTherefore the molarity of H+1+1 ions will be ions will be the same as the molarity of the acidthe same as the molarity of the acid

Once the HOnce the H+1+1 molarity is determined, the molarity is determined, the pH can be determinedpH can be determined

pH = -log [HpH = -log [H+1+1]]

Example #5Example #5

Determine the [HDetermine the [H+1+1] from the acid concentration] from the acid concentrationHNOHNO33 H H+1+1 + NO + NO33

-1-1

0.10 M HNO0.10 M HNO33 = _____ M H = _____ M H+1+1

Enter the [HEnter the [H+1+1] concentration into your ] concentration into your calculator and press the calculator and press the loglog key key

log(0.10) = ___log(0.10) = ___ Change the sign to get the pHChange the sign to get the pH

pH = _________pH = _________

Calculate the pH of a 0.10 M HNO3 solution

Buffered SolutionsBuffered Solutions Buffered SolutionsBuffered Solutions __________ in pH when an __________ in pH when an

acid or base is added to it.acid or base is added to it. Used when need to maintain a certain pH in the Used when need to maintain a certain pH in the

system, eg. Blood.system, eg. Blood. A buffer solution contains a __________ and its A buffer solution contains a __________ and its

conjugate _______conjugate _______ Buffers work by reacting with added ____ or ___ Buffers work by reacting with added ____ or ___

ions so they do not accumulate and change the ions so they do not accumulate and change the pH.pH.

Buffers will only work as long as there is sufficient Buffers will only work as long as there is sufficient weak acid and conjugate base molecules present.weak acid and conjugate base molecules present.

BuffersBuffers

pH ProblemspH Problems

What is the pH of 6M hydrochloric acid? _____What is the pH of 6M hydrochloric acid? _____

Name(s):___________Name(s):___________