Finding pH

© 2011 Pearson Education, Inc.

Chapter 14 – Acids and Bases

4. Which of the following metals does not react with hydrochloric acid?

A. Calcium

B. Copper

C. Magnesium

D. Zinc

Acid PropertiesAcid Properties Sour taste (grape fruit)Sour taste (grape fruit) Found in many fruits Found in many fruits VinegarVinegar Will burn if not dilutedWill burn if not diluted Made up of NonmetalsMade up of Nonmetals Acid formulas usually start Acid formulas usually start

with hydrogen- ex HCl, Hwith hydrogen- ex HCl, H22SOSO44

Base PropertiesBase Properties Bitter taste Slippery feel Most household cleaners Also dangerous if not diluted Made up of a metal and

nonmetals in formulas Arrhenius bases start with metals

in their formulas and end with a OH- ex NaOH, KOH, Ba(OH)2

Arrhenius TheoryArrhenius Theory AcidsAcids release hydrogen release hydrogen

ions ions (H(H++)) HCl → HCl → HH++ + Cl + Cl--

BasesBases release hydroxide release hydroxide ions ions (OH(OH--))

NaOH → NaNaOH → Na++ + + OHOH--

Strong Acids will completely ionize

7

Know the strong Know the strong acids & bases!acids & bases!

Brønsted-Lowry Theory Brønsted-Lowry Theory D7C20D7C20

ACIDACID: any substance that : any substance that donatesdonates a a proton (hydrogen proton (hydrogen ionion) )

BASEBASE: any substance that : any substance that acceptsaccepts a a proton (hydrogen proton (hydrogen ionion))

MUST MUST occur together; Can not gain occur together; Can not gain unless something else losesunless something else loses

Chemical Reactions: New products are formed Differ by ONLY H+

Brønsted-Lowry TheoryBrønsted-Lowry Theory HCl + HHCl + H22O → HO → H33OO++ + Cl + Cl--

acid base C.A. C.B.acid base C.A. C.B. Conjugate acidConjugate acid –the PRODUCT –the PRODUCT

obtained after a BASE gains a obtained after a BASE gains a proton (hydrogen ion)proton (hydrogen ion)

Conjugate baseConjugate base –the PRODUCT –the PRODUCT obtained after an ACID donates a obtained after an ACID donates a proton (hydrogen ion)proton (hydrogen ion)

Conjugate PairsConjugate Pairs

Hydronium ion Hydronium ion – An ion – An ion formed when a free Hformed when a free H++

forms with water to form forms with water to form an Han H33OO++

Why is Water Neutral?Why is Water Neutral?

When one water gains, When one water gains, another loses a H+another loses a H+

[H[H33O+ ] = [OH-]O+ ] = [OH-]

1414

WaterWater

H2O can function as both an ACID

and a BASE.Equilibrium constant for water

= Kw

Kw = [H3O+] [OH-] =

1.00 x 10-14 at 25 oC

AUTOIONIZATION

1515

WaterWater

Kw = [H3O+] [OH-] = 1.00 x 10-14 at 25 oC

In a neutral solution [H3O+] = [OH-]

so [H3O+] = [OH-] = 1.00 x 10-7 M

OH-

H3O+

OH-

H3O+

Autoionization

Kw = 1.00 x 10-14 ONLY at 25 oC (depends on T)

1616

[H[H33OO++], [OH], [OH--] and pH] and pH

A common way to express acidity and basicity is with pH

pH = - log [HpH = - log [H33OO++]]

In a neutral solution, [H3O+] = [OH-] =

1.00 x 10-7 at 25 oC

pH = -log (1.00 x 10-7) = - (-7) = 7

The pH scale only for water

solutionsBasic = more OH-

Acidic = more H3O+

Neutral H3O+ = OH-

Why at a pH = 7 ?Why at a pH = 7 ?

Determined by concentration [ X ] of Determined by concentration [ X ] of each ioneach ion

[H+ ]= [OH-] = 10[H+ ]= [OH-] = 10--77MM

The concentration of hydrogen ion The concentration of hydrogen ion equals the concentration of hydroxide equals the concentration of hydroxide

ion equals ten to the negative ion equals ten to the negative seventh molar concentrationseventh molar concentration

Need to remember molarity and concentrationNeed to remember molarity and concentration

Any pAny pXX Scales ScalesAny pAny pXX Scales Scales

In generalIn general pX = -log XpX = -log X

pOH = - log pOH = - log [OH[OH--]]

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

Determining pOHDetermining pOH

pH + pOH = 14If know one can determine the other.

If pH = 13, what is the pOH?13 + pOH = 14

pOH = 14 – 13 = 1

2121[H[H33OO++], [OH], [OH--] and pH] and pH

What is the pH of 0.0010 M NaOH(aq)?

[OH-] = 1.0 x 10-3 M

[H3O+] = 1.0 x 10-11 M

pH = - log (1.0 x 10-11) = 11.00

General conclusion —

Basic solution pH > 7

Neutral pH = 7 Acidic solution pH < 7

2222

[H[H33OO++], [OH], [OH--] and pH] and pH[H[H33OO++], [OH], [OH--] and pH] and pH

If the pH of Coke is 3.12, it is ________.

log [H3O+] = - pH = - 3.12

Take antilog and get

[H3O+] = 10-pH

[H3O+] = 10-3.12 =

7.6 x 10-4 M

ACID

2323

Calculate pHIF [OH-] = 4.2 x 10-4 M

so pOH = - log [OH-] = 3.37

pH + pOH = 14,

pH = 10.63

14.7SAMPLE PROBLEM

© 2011 Pearson Education, Inc.

Calculating pH Determine the pH for a solution with [H3O

+] = 5 10–8 M.

SOLUTION

STEP 1 Press the log key Enter the [H3O+] value.

STEP 2 change the sign.

STEP 3 Adjust the number of significant figures on the right of the decimal point to equal the SFs in the coefficient.

14.9SAMPLE PROBLEM

Calculating [H3O+] from pH

Calculate [H3O+] for a solution of baking soda with a pH of 8.25.

STEP 1 Change the sign of pH

STEP 2 enter the negative pH as the exponent : 10 -pH

STEP 3 Write the display with units of concentration

5.62341 × 10–9 M

Adjust the significant figures in the coefficient. Because the pH value of 8.25 has two digits on the right of the decimal point, the

[H3O+] is written with two significant figures:

[H3O+] = 5.6 10–9 M

© 2011 Pearson Education, Inc.

Chapter 14 – Acids and Bases

9. What is the [H+] of a solution at pH 3.5?

A. 5.3 x 10-5

B. 6.0 x 10-4

C. 3.16 x 10-4

D. 8.84 x 10-3

2828Calculating [HCalculating [H33OO++] & ] & [OH[OH--]]

0.0010 mol of NaOH ia added to 1.0 L of pure water: Calculate

[H3O+] and [OH-].

[NaOH] = [OH-]= 1.0 10–3 MNaOH → Na+ + OH-

[OH-] = 10 -3 M than pOH = 3.00

pH = 14 – 3.00 = 11.00

[H3O+] = 1.0 10 -11 M

Determining Determining [H[H33OO++] ]

If pH = 6 than [H3O+] = 10 -6 M..The pH value is the negative

exponent for the concentration of hydrogen ions in solution. .

If pH = If pH = Y Y than [Hthan [H33OO++] = 10 ] = 10 --YY M M

Determining Determining [[OHOH--] ] If pOH = 10 than [OH-] = 10 -10 M

The value of pOH is used as the negative exponent for the concentration of the hydroxide ions in solutions .

pOH = X than [OH-] = 10 -X M