Look at some examples, and Look at some examples, and see if you can figure out see if you can figure out what an acid is…what an acid is…

HCl (Hydrochloric acid)HCl (Hydrochloric acid)

HNOHNO3 3 (Nitric acid)(Nitric acid)

HH22SOSO44 (Sulfuric acid) (Sulfuric acid)

HH33POPO44 (Phosphoric acid) (Phosphoric acid)

Acid/Base definitionsAcid/Base definitions

Definition #1: Arrhenius (traditional) Definition #1: Arrhenius (traditional)

Acid – has hydrogen in the formula, and produces HAcid – has hydrogen in the formula, and produces H++ ions in water ions in water

Base – has OH in the formula, and produces OHBase – has OH in the formula, and produces OH-- ions ions in waterin water

Acids and bases in water:Acids and bases in water:

Arrhenius Acid:Arrhenius Acid:

HCl (aq) HCl (aq) H H++ + Cl + Cl--

HCl is an acid because it has H in the formula, HCl is an acid because it has H in the formula, and increases the amount of Hand increases the amount of H++ in water. in water.

Arrhenius Base:Arrhenius Base:

NaOH (aq) NaOH (aq) Na Na++ + OH + OH--

NaOH is a base because it has OH in the formula NaOH is a base because it has OH in the formula and increases the amount of OHand increases the amount of OH-- in water. in water.

The Arrhenius definition The Arrhenius definition had a problem…had a problem…

Some bases (like ammonia, NHSome bases (like ammonia, NH33) don’t ) don’t

have OH in the formula.have OH in the formula.

Bronsted-Lowry definitions:Bronsted-Lowry definitions:

(new and improved definitions)(new and improved definitions)

Acids are substances that Acids are substances that give away give away hydrogen hydrogen ions. (This definition is practically the same.)ions. (This definition is practically the same.)

Bases are substances that Bases are substances that acceptaccept hydrogen ions. hydrogen ions.

Bronsted-Lowry Bronsted-Lowry definition:definition:

Acids are substances that give away hydrogen Acids are substances that give away hydrogen ions.ions.

Example: HCl gives away hydrogen to water: Example: HCl gives away hydrogen to water:

HCl (aq) + HHCl (aq) + H22O O H H33O+ (aq) + Cl- (aq)O+ (aq) + Cl- (aq)

Draw the hydrogen ion. What does it consist of?Draw the hydrogen ion. What does it consist of?

A hydrogen ion is simply A hydrogen ion is simply a proton.a proton.

Acids are also called “proton donors.”Acids are also called “proton donors.”

Bronsted-Lowry Bronsted-Lowry definition:definition:

A base is a hydrogen ion acceptor.A base is a hydrogen ion acceptor.

Another way of saying the same thing:Another way of saying the same thing:

A base is a proton acceptor.A base is a proton acceptor.

An acid is a proton donorA base is a proton acceptor

acidbase

Practice question:Practice question:

In the reactionIn the reaction

HBr(HBr(aqaq) + NH) + NH33((aqaq) ) NH NH44++((aqaq) + Br) + Br––((aqaq) )

Identify the acid and the base.Identify the acid and the base.

Practice questionPractice question

In the reactionIn the reaction

HSOHSO44–– + H + H22O O H H33OO++ + SO + SO44

2-2-

Identify the acid and the base.Identify the acid and the base.

Practice question:Practice question:

In the equationIn the equation

HCl(HCl(gg) + H) + H22O(O(ll) ) H H33OO++((aqaq) + Cl) + Cl––((aqaq))

which formula is a Brønsted-Lowry acid?which formula is a Brønsted-Lowry acid?

Tell-tale signs of an acid:Tell-tale signs of an acid:

sour tastesour taste(orange juice and lemonade contain (orange juice and lemonade contain

citric acid)citric acid) turns litmus paper redturns litmus paper red (by reacting with a chemical in (by reacting with a chemical in the litmus paper)the litmus paper) reacts with metals to producereacts with metals to produce

hydrogen gashydrogen gas

Chemists write the formulas for acids Chemists write the formulas for acids with the H at the front, so they’re easy with the H at the front, so they’re easy to identify as acids:to identify as acids:

HCl (Hydrochloric acid)HCl (Hydrochloric acid)

HNOHNO3 3 (Nitric acid)(Nitric acid)

HH22SOSO44 (Sulfuric acid) (Sulfuric acid)

HH33POPO44 (Phosphoric acid) (Phosphoric acid)

Tell-tale signs of a base:Tell-tale signs of a base:

bitter tastebitter taste slippery feelslippery feel turns litmus paper blueturns litmus paper blue

(Conveniently, base, bitter, and blue all (Conveniently, base, bitter, and blue all start with B!)start with B!)

Some substances, Some substances, like water act like an like water act like an acid sometimes and acid sometimes and act like a base other act like a base other times.times.

Substances that can act as an Substances that can act as an acid or a base are calledacid or a base are called

amphoteric.amphoteric.

Neutralization reactions:Neutralization reactions:If you combine an acid with If you combine an acid with a base…a base…

Predict the products:Predict the products:

HCl + NaOH HCl + NaOH ? ?

Hint: It’s a special kind of double replacement Hint: It’s a special kind of double replacement reaction!reaction!

If you combine an acid with If you combine an acid with a base…a base…

HCl + NaOH HCl + NaOH H H22O + NaClO + NaCl

This is called a This is called a neutralization reactionneutralization reaction because the acid and base neutralize because the acid and base neutralize each other.each other.

If you combine an acid with If you combine an acid with a base…a base…

HCl + NaOH HCl + NaOH H H22O + NaClO + NaCl

The products of any neutralization reaction The products of any neutralization reaction are water and a salt.are water and a salt.

Acid/Base reactions:

Produce water and a salt (and sometimes carbon dioxide).

Hint: concentrate on the water first. Remember, water has the formula HOH.

Complete and balance the following:

HCl + KOH

HCl + Ca(OH)2

HOH + KCl

2

Require equal numbers

2HOH + CaCl2

1. Ba(OH)2 + H3PO4

2. HC2H3O2 + NaOH

3. H2SO4 + KOH

4. H2CO3 + NaOH

Everyday application:Everyday application:

The stomach secretes acids to help digest The stomach secretes acids to help digest foods. These acids, which include foods. These acids, which include hydrochloric acid, have a molarity of about hydrochloric acid, have a molarity of about 0.1M.0.1M.

Antacids, like Tums, Maalox, Mylanta and Alka-Antacids, like Tums, Maalox, Mylanta and Alka-seltzer are simple bases that neutralize seltzer are simple bases that neutralize stomach acids.stomach acids.

Acids and Bases: Acids and Bases: StrengthStrength

What makes an acid a strong acid?What makes an acid a strong acid?It ionizes completely in water!It ionizes completely in water!

These are strong acids (in order of increasing These are strong acids (in order of increasing strength):strength):

1.1. HNOHNO33 (nitric acid) (nitric acid)2.2. HCl (hydrochloric acid)HCl (hydrochloric acid)3.3. HBr (hydrobromic acid)HBr (hydrobromic acid)4.4. HI (hydroiodic acid)HI (hydroiodic acid)5.5. HH22SOSO44 (sulfuric acid) (sulfuric acid)6.6. HClOHClO44 (perchloric acid) (the strongest) (perchloric acid) (the strongest)

Strong acids:Strong acids:

HCl + HHCl + H22O O H H33OO++ + Cl- + Cl-

Remember, strong acids ionize completely in water. The reaction goes all the way to the right. A single arrow is used. There are virtually no HCl molecules left intact.

One more reminder:One more reminder:

“Weak” does not mean the same “Weak” does not mean the same thing as “diluted.”thing as “diluted.”

HCl, for example is always a strong HCl, for example is always a strong acid. If you add 1000 liters of water acid. If you add 1000 liters of water to it, it will be diluted, but still to it, it will be diluted, but still strong because what little there is strong because what little there is will be will be completely dissociated.completely dissociated.

Electrolytes:Electrolytes:

Acids and bases are both examples of Acids and bases are both examples of electrolytes.electrolytes.

Electrolytes are compounds that form ions Electrolytes are compounds that form ions when dissolved in water.when dissolved in water.

They’re called electrolytes because they They’re called electrolytes because they can conduct electricity through water.can conduct electricity through water.

More on electrolytes:More on electrolytes:If two wires connected to a If two wires connected to a light bulb and to a power and to a power

source are placed in a source are placed in a beaker of water, the light of water, the light bulb will not bulb will not glow. If an electrolyte, such as . If an electrolyte, such as sodium sodium chloride, is dissolved in the water, the light , is dissolved in the water, the light bulb will glow because the solution can now bulb will glow because the solution can now conduct electricity. The amount of electric current conduct electricity. The amount of electric current that can be carried by an electrolyte solution is that can be carried by an electrolyte solution is proportional to the number of ions dissolved. proportional to the number of ions dissolved. Thus, the bulb will glow more brightly if the Thus, the bulb will glow more brightly if the amount of sodium chloride in the solution is amount of sodium chloride in the solution is increased. increased.

Practice QuestionsPractice Questions

Which of these could be Which of these could be used to determine used to determine whether a substance is a whether a substance is a base?base?

A Thermometer A Thermometer B Litmus paper B Litmus paper C Balance C Balance D Bunsen burnerD Bunsen burner

An element common to An element common to all acids is –all acids is –

a. chlorinea. chlorineb. hydrogenb. hydrogenc. oxygenc. oxygend. sodiumd. sodium

The pH Scale…The pH Scale…

The The pH scalepH scale is a way of is a way of expressing the expressing the concentration of acids. concentration of acids.

Under 7 = acidUnder 7 = acid 7 = neutral 7 = neutral

Over 7 = base Over 7 = base

pH is the negative log of pH is the negative log of the Hthe H++ concentration. concentration.

pH is the negative log of pH is the negative log of the Hthe H++ concentration. concentration.

What????

It’s easier than it sounds!It’s easier than it sounds!

If HIf H+ + is….is….

1 x 101 x 10-3-3 pH = 3 pH = 3

1 x 101 x 10-7-7 pH = 7 pH = 7

1 x 101 x 10-12-12 pH = 12 pH = 12