Acids and Bases

Chapter 19

Acids

• pH less than 7• Sour taste• Conduct electricity• Reacts with metals to

produce hydrogen gas• Higher [H+]

concentration

Brønsted-Lowry AcidSome Common Acids

Name Formula

Hydrochloric acid HCl

Nitric acid HNO3

Sulfuric acid H2SO4

Phosphoric acid H3PO4

Ethanoic acid CH3COOH

Carbonic acid H2CO3

• Compounds that donate protons (H+)

• Polyprotic compounds

Acids

•a HYDRONIUM ION is the ion formed when a water molecule gains a hydrogen ion

•H3O+

To summarize...

•An acid is a chemical that dissolves in water to create more H+ ions than there are in neutral water

Bases

• pH greater than 7

• Bitter taste• Slippery feel• Higher [OH-]

concentration

Brønsted-Lowry Bases

•compounds that accept protons (H+)

Some common basesSome Common Bases

Name Formula Solubility in Water

Sodium hydroxide NaOH High

Potassium hydroxide KOH High

Calcium hydroxide Ca(OH)2 Very low

Magnesium hydroxide Mg(OH)2 Very low

to summarize...

•A base is a chemical that dissolves in water to create fewer H+ ions than there are in neutral water, or more OH- ions

Bronsted-Lowry Theory

•Ammonia gains a proton, so it is a base

•Water donates a proton, so it is an acid

Conjugate Acid•the ion or molecule formed

when a base gains a hydrogen ion.

Conjugate Base

•the ion or molecule that remains after an acid loses a hydrogen ion.

Conjugate acids and bases

Some Conjugate Acid-Base Pairs

Acid Base

HCl Cl–

H2SO4 HSO4–

H3O+ H2O

HSO4– SO4

2–

CH3COOH CH3COO–

H2CO3 HCO3−

HCO3– CO3

2–

NH4+ NH3

H2O OH–

Amphoteric Substances

•A substance is AMPHOTERIC if it can act as either an acid or a base, such as water

Identify each reactant as a Bronsted-Lowry acid (hydrogen-ion donor) or base (hydrogen-ion acceptor).

1.HNO3 + H2O H3O+ + NO3-

2.CH3COOH + H2O ↔ H3O+ + CH3COO-

3.NH3 + H2O ↔ NH4+ + OH-

4.H2O + CH3COO- ↔ CH3COOH + OH-

Identify the conjugate acid-base pairs of each reaction.

1.HNO3 + H2O H3O+ + NO3-

2.CH3COOH + H2O ↔ H3O+ + CH3COO-

3.NH3 + H2O ↔ NH4+ + OH-

4.H2O + CH3COO- ↔ CH3COOH + OH-

Acid/Base Reactions• Acids and bases react to produce

salt and water in a neutralization reaction.

H2SO4 + 2NaOH Na2SO4 + 2H2O acid base salt water

Self-ionization of water

•the reaction in which water molecules produce ions

Self-ionization of water

• In pure water at 25°C, the concentration of hydrogen ions is only 1 × 10−7M.

• The concentration of OH− is also 1 × 10−7M because the numbers of H+ and OH− ions are equal in pure water.

• Any aqueous solution in which [H+] and [OH−] are equal is a neutral solution.

Ion-product constant for water•The product of the concentrations

of the hydrogen ions and the hydroxide ions in water is called the ion-product constant for water (Kw).

Kw = [H+] × [OH−] = 1.0 × 10−14

in acidic solutions...

•When acids dissolve in water hydrogen ions are released:

•HCl(aq) → H+(aq) + Cl−(aq)

•The H+ concentration is greater than the OH- concentration.

•A solution in which [H+] is greater than [OH−] is an acidic solution.

–The [H+] is greater than 1 × 10−7M.

in basic solutions...

•When bases dissolves in water, it forms hydroxide ions in solution.

•NaOH(aq) → Na+(aq) + OH−(aq)

•The H+ concentration is less than the OH- concentration.

•A basic solution is one in which [H+] is less than [OH−].

let’s practice...

•If the [H+] in a solution is 1.0 × 10−5M, is the solution acidic, basic, or neutral? What is the [OH−] of this solution?

The pH concept•The negative logarithm of the

hydrogen-ion concentration.

pH = -log [H+]

Calculating pH from [H+]

IF given in scientific notation in this form:

1.0 x 10 –x (x being any negative number)

then the exponent on the 10 is the pH value.

Example:1.0 x 10-3 M pH= 3

ExampleWhat are the pH values of the following three solutions, based on their hydrogen ion concentrations?

1.[H+]= 1.0 x 10-5 M2.[H+]= 1.0 x 10-9 M3.[H+]= .001 M

ExampleWhat are the pH values of the following three solutions, based on their hydrogen ion concentrations?

1.[H+]= 1.0 x 10-5 M pH =52.[H+]= 1.0 x 10-9 M pH = 93.[H+]= .001 M pH= 3

Calculating pH from [H+]

If the coefficient is not 1.0 then do the math.

Example:What is the pH of a solution with a hydrogen-ion concentration of 4.2 x10-

10 M?

Calculating [H+] from pH

IF the pH value is an integer (i.e. 1, 2, 3, 4, 5…) then the [H+]= 1.0 x 10 -1,-2,-3,-4,-5…

ExamplepH = 4 [H+] = 1.0 x 10-4

If NOT, then math[H+] = antilog(-pH)

In calculator, the antilog function: Second, log

Example: The pH of an unknown solution is 6.35. What is hydrogen-ion [H+] concentration?

Calculating pH from [OH-]

Use the ion-product constant for water to solve for [H+] and then find pH.

Kw = [H+] × [OH−] = 1.0 × 10−14

Example: What is the pH of a solution if [OH-]= 4.0 x 10 -11 ?

Strong/Weak Acids

Strong acids will completely ionize in aqueous solutions.

Weak acids will not ionize completely in aqueous solutions CH3COOH (aq) + H20 (l) ↔ H3O+ (aq) + CH3OO- (aq)

Strong/Weak Acids/Bases

Strong bases dissociates completely into metal ions and hydroxide ions in aqueous solutions

Weak bases reacts with water to form the conjugate acid of the base and hydroxide ions

Substance Formula

Hydrochloric acidNitric acidSulfuric acid

HClHNO3

H2SO4

Phosphoric acid H3PO4

Ethanoic acid CH3COOH

Carbonic acid H2CO3

Hypochlorous acid HClO

Ammonia NH3

Sodium silicate Na2SiO3

Calcium hydroxideSodium hydroxidePotassium hydroxide

Ca(OH)2

NaOHKOH

Strong acids

Strongbases

Identify each compound as a strong or weak acid or base.

1.NaOH2.NH3

3.H2SO4

4.HCl

Nomenclature for Acids

•The naming system depends on the suffix of the anion: -ide, -ite, and –ate.

•HnX

Nomenclature for Acids

1. When the name of the anion ends in –ide, the acid name begins with the prefix hydro-. The stem of the anion has the suffix –ic and is followed by the word acid.

Ex.HCl anion= chlorideHydrochloric acid

Nomenclature for Acids

2. When the anion name ends in –ite, the acid name is the stem of the anion with the suffix –ous, followed by the word acid.

Ex.

H2SO3 anion= sulfite

Sulfurous acid

Nomenclature for Acids

3. When the anion name ends in –ate, the acid name is the stem of the anion with the suffix –ic, followed by the word acid.

Ex.

HNO3 anion= nitrate

Nitric acid

Write the name of the following acids

1.HF2.HNO3

3.H2SO3

Nomenclature for acids•Look at the ions being used and write the

formula like an ionic compound

Ex.

Hydrobromic acid anion= bromide (rule 1)

H+ Br- = HBr

Phosphoric acid anion= phosphite (rule 2)

H+ PO3-3 = H3PO3

Sulfuric acid anion= sulfate (rule 3)

H+ SO4-2 = H2SO4

Write the formula of the following

acids

1.Perchloric acid2.Hydroiodic acid3.Chlorous acid

Nomenclature for Bases

•The formula and names are the same as ionic compounds

NaOH = sodium hydroxide

Aluminum hydroxide = Al+3 OH-

Al(OH)3

Write the name of the following bases

1.Ba(OH)2

2.Ca(OH)2

3.RbOH

Write the formulas of the following

bases1.Cesium hydroxide2.Beryllium hydroxide3.Manganese

hydroxide