Acids & Bases

They are everywhere..

In your food

In your house

EVEN IN YOU!!!!!

What is an acid?• An acid is a solution that has an excess of

H+ ions. It comes from the Latin word

acidus that means "sharp" or "sour".

• The more H + ions, the more acidic the

solution.

Properties of an Acid

• Tastes Sour

• Conduct Electricity

• Corrosive, which means they

break down certain substances.

Many acids can corrode fabric,

skin,and paper

• Some acids react strongly with

metals

• Turns blue litmus paper red

Picture from BBC Revision Bites

http://www.bbc.co.uk/schools/ks3bitesize/science/chemistry/acids_b

ases_1.shtml

Uses of Acids

• Acetic Acid = Vinegar

• Citric Acid = lemons, limes, & oranges. It is in many sour candies such as lemonhead & sour patch.

• Ascorbic acid = Vitamin C which your body needs to function.

• Sulfuric acid is used in the production of fertilizers, steel, paints, and plastics.

• Car batteries

What is a base?

• A base is a solution that

has an excess of OH-

ions.

• Another word for base

is alkali.

• Bases are substances

that can accept

hydrogen ions

Properties of a Base

• Feel Slippery

• Taste Bitter

• Corrosive

• Can conduct electricity.

(Think alkaline batteries.)

• Do not react with metals.

• Turns red litmus paper blue.

Uses of Bases• Bases give soaps, ammonia,

and many other cleaning products some of their useful properties.

• The OH- ions interact strongly with certain substances, such as dirt and grease.

• Chalk and oven cleaner are examples of familiar products that contain bases.

• Your blood is a basic solution.

pH Scale

• pH is a measure of how acidic or basic a

solution is.

• The pH scale ranges from 0 to 14.

• Acidic solutions have pH values below 7

• A solution with a pH of 0 is very acidic.

• A solution with a pH of 7 is neutral.

• Pure water has a pH of 7.

• Basic solutions have pH values above 7.

pH Scale

• A change of 1 pH unit represents a tenfold change in the acidity of the solution.

• For example, if one solution has a pH of 1 and a second solution has a pH of 2, the first solution is not twice as acidic as the second—it is ten times more acidic.

Acid – Base Reactions

• A reaction between an

acid and a base is called

neutralization. An acid-

base mixture is not as

acidic or basic as the

individual starting

solutions.

Molarity

• Molar concentration (M) defines the

number of moles of a species per

litre of solution (mol.L-1)

• One mole is the formula weight of a

substance expressed in grams.

Molarity Example

• Na2SO4 has a formula weight (molar

mass) of 142 g

• A one litre solution containing 14.2 g

of Na2SO4 has a molarity of 0.1 M

(mol.L-1)

• Na2SO4 dissociates in water:

Na2SO4 = 2Na+ + SO42-

• The molar concentrations of Na+ and

SO 2- are 0.2 M and 0.1 M

Definitions of Acids and Bases:

• Arrhenious Acids and Bases

• Bronstead Lowry Acids and Bases

• Acid: a substance that produces H3O+

when dissolved in water.

• Base: a substance that produces OH-

when dissolved in water.

• Arrhenius acids and bases are limited to

water solutions.

Arrhenius Acids and Bases

** This definition is not

very flexible**

• Acid: proton donor.

• Base: proton acceptor.

• Bronsted-Lowry acid base

reaction: proton transfer from acid

to base.

Bronsted-Lowry Acids and Bases style

• Conjugate Acid-Base Pairs: two

species that differ by a proton.

• Acid : the species that contains the

proton that is transferred.

• Conjugate base: the species formed by

loss of the proton.

HF(aq) + H2O(l) ⇌ F-(aq) + H3O+(aq)

• HF and F- make up an acid-base

conjugate pair. F- is the conjugate base

of HF.

Conjugate Acid-Base Pairs

Acid Base

HCl Cl -

H2SO4 HSO4-

HSO4- SO4

2-

NH4+ NH3

H3O+ H2O

H2O OH-

H2O is amphoteric - it acts as both

an acid and a base.

Acid-Base Conjugate Pairs

acid + base⇌ conj. base + conj. acid

HF + NH3 ⇌ F- + NH4+

HCl + H2O ⇌ Cl- + H3O+

H2O + NH2- ⇌ OH- + NH3

Bronsted-Lowry Acid-Base Reactions

Identify the acid-base conjugate pairs

HNO2(aq) + H2O(l) ⇌ H3O+(aq) + NO2

-(aq)

CH3NH2(aq) + H2O(l) ⇌ CH3NH3+(aq) + OH-(aq)

Test Your Skill

H2O(l) + H2O(l) ⇌ H3O+(aq) + OH-(aq)

• H3O+ and H2O are a conjugate acid-

base pair.

• H3O+ and OH - are a conjugate acid-

base pair.

Autoionization of Water

H2O(l) + H2O(l) ⇌ H3O+(aq) + OH-(aq)

• The equilibrium constant for this

reaction is called Kw.

• Kw = [H3O+][OH -]

• Kw changes with temperature and is

equal to 1.0 × 10-14 at 25o C.

Autoionization of Water

H2O(l) + H2O(l) ⇌ H3O+(aq) + OH-(aq)

• In pure water, [H3O+] = [OH -].

Kw = [H3O+][OH -] = 1.0 × 10-14

Kw = [H3O+]2 = 1.0 × 10-14

• [H3O+] = [OH -] = 1.0 × 10-7 M

Calculating Hydrogen and Hydroxide Ion

Concentrations

• Adding an acid or a base to water

causes the H3O+ and OH-

concentrations to change.

• Calculate the hydroxide ion

concentration of a solution in which

the hydrogen ion concentration is

3.6 × 10-3 M.

Acidic or Basic Solutions

• Calculate the hydrogen ion

concentration in a solution in which

the hydroxide ion concentration is

0.025 M.

Test Your Skill

Calculating pH:

Identifying Acids and Bases

• Acids have a ph from 0-7

• Lower pH value indicates

a stronger acid.

• Bases have a pH from

7-14

• Higher pH value indicates

a stronger base.

• Calculate the hydrogen ion concentration

in a solution that has a pH of 3.52.

Calculating Hydrogen Ion Concentration from

pH

[H3O+][OH-] = Kw = 1.0 × 10-14

log([H3O+][OH-]) = log Kw

log[H3O+] + log[OH-] = log Kw

-log[H3O+] - log[OH-] = -log Kw

pH + pOH = pKw

pH + pOH = 14.00

Relating pH and pOH

• HA(aq) + H2O(l) H3O+(aq) +A-(aq)

• Strong acids ionize completely in

solution.

• Memorize the six common strong acids:

HCl, HBr, HI, HNO3, HClO4, and H2SO4.

100%

Strong Acids and Bases

• Calculate the pOH of a 0.050 M HCl

solution.

pH of a Strong Acid Solution

• Strong bases quantitatively produce

hydroxide ions in water.

• The most common strong bases are the

group IA and soluble IIA oxides and

hydroxides.

Strong Bases

• Calculate the pH of a 0.035 M Ba(OH)2

solution.

pH of a Strong Base Solution

What is the concentration of a solution of

HCl if the pH is 3.75?

What is the concentration of a solution of

KOH if the pH is 11.60?

Test Your Skill

Titration Equipment

• Stand

• Buret

• Buret clamp

• Erlenmeyer Flask (diagram shows a beaker)

• Analyte (unknown molarity)

• Titrant (standard solution of known molarity)

• Indicator

• pH meter (optional, but highly recommended)

• Stirrer (optional, recommended)

Around the Endpoint

• You have reached the

endpoint when the

indicator first

permanently changes

color.

• There will be a very

large jump in pH as all

of the analyte is

reacted, and there is

now excess titrant. Example of a solution using

phenolphthalein as a indicator.

The reaction has just reached

the equivalence point, because

the solution has just

permanently turned pale pink.

37

Molarity

Let’s start our discussion of solution concentration

Measurement with

Molarity: the most common solution concentration

measurement is defined as follows:

M = moles of solute

LITERS of solution

Which means Molarity = # of moles per liter of solution

MOLARITY

Capital M

38

Molarity

Let’s Consider the following Problem:

What is the molarity of a solution in which 50g of

CuSO4 is dissolved in water to make a 2 liter solution.

Step 1. What’s the formula for MOLARITY?

M = moles of solute

liters of solution

39

Molarity

Step 2. We need to determine how many moles we have

in 50g of CuSO4 .

How do we do that? Remember the mole Hole?

- 1. Determine the molar mass of CuSO4

(159.5g/mol)

- 2. Calculate the # of moles of CuSO4

Since we’re going into the mole hole we need

to DIVIDE # of grams by molar mass

(50/159.5) = 0.31 moles

40

Molarity

Step 3. Calculate the Molarity of the solution using

the formula for MOLARITY

M = moles of Solute

liters of solution

How many moles do we have?

How many liters do we have?

So M = 0.31 moles

2 liters M = 0.155 mol/liter

0.31 mol

2 L

41

Molarity by dilution

In a titration the endpoint is reached when the

moles of each substance are equalt.

However, the moles are not provided only volume and

concentration. Therefore,

M1 x V1 = M2 x V2

If we know three values we can calculate the 4th.

Let’s see how we use this relationship

42

Dilution Problem

What is the concentration of Nitric acid if 12ml of

the acid reaches an equivalence point when 30ml

of 1.6M sodium hydroxide is added to it.

M1 x V1 = M2 x V2

[acid] x 12ml = [1.6M] x 30ml

[acid] x Volume acid = [base] x Volume base