Chapter 9Section 1

Acids, Bases, and pH

Explain the chemical composition of acids and bases, and explain the change of pH in neutralization reactions.

D12

I can differentiate between acids and bases.

Learning Target

When dissolved in water, they ionize (form ions)

Form H+ (Hydrogen) ions, which attach to water molecules to form hydronium ions, H3O+

Properties:Taste sourBlue litmus paper turns redConduct electric currentCorrosive

Acids

Strong and Weak Acids

Complete ionization in waterHigh concentration of hydronium ions in the

liquidStrong acid Conducts electricityStrong electrolyte

HNO3 + H2O H3O+ + NO3-

Strong Acids

Weak acidsLow concentration of hydronium ions in the

liquidDo not conduct electricity wellWeak electrolyteDouble headed arrow

CH3COOH + H2O H3O+ + CH3COO-

Weak Acids

CorrosiveCan damage living tissuesVapors can be harmful to eyes, mouth and

lungsWear safety goggles, gloves, lab apron

Acid Safety

When dissolved in water form OH- (hydroxide ions)

PropertiesTastes bitterSolution feels slipperyTurn red litmus paper blueLike acids, bases can also damage the skin

Bases

Strong and Weak Bases

When bases dissolve in water, they ionize.

NaOH Na+ + OH-

Not all bases contain OH- Some will react with water to form hydroxide

ion

NH3 + H2O NH4+ + OH-

Bases

High concentration of OH- in the solution

Ba(OH)2 Ba2+ + 2OH-

Complete ionization in waterGood conductor of electricityStrong electrolyte

Strong Bases

Low concentration of OH- in solution

NH3 + H2O NH4+ + OH-

Do not ionize completelyNot a good conductor of electricityWeak electrolyte

Weak Bases

Bases are corrosive and can damage living tissue

Wear safety goggles, gloves and a lab apron!!

Base Safety

What ions do acids produce?What ions do bases produce?What is the difference between a strong acid

and a weak acid?Why should we observe lab safety rules when

working with acids and bases?

Let’s Review

I can explain pH.

Learning Target

You can determine if a substance is an acid or a base by using an indicator.

An indicator is a substance that changes color in the presence of an acid or base.

Indicators measure the level of hydronium ions. The level determines if a substance is acidic or basic.

Detecting Acids and Bases

Cabbage juice can be used as an indicator

Litmus paper is a common indicatorAcids turn blue litmus

paper redBases turn red litmus

paper blueOnly indicates if a

substance is an acid or a base

To determine strength or weakness, pH values are used

Indicators

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A measure of the concentration of H3O+ ions in solution

Acidity or basicity of a solution can be criticalEnzymes in your body will not

function properly if your blood is too basic or acidic

Fish cannot survive in waters that are too acidic or basic

pH

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Con

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pH Scale

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14

Neu

tral

P

ure

H2O

[H+] [OH-]

Acids Bases

Stronger Weaker Weaker Stronger

Acid: substance that produces H+ ions in aqueous

solution

Base: substance that produces OH-

ions in aqueous solution

pH• Small differences in pH

mean large differences in acidity

• Example:pH of coke = 3pH of coffee = 5

Coke is 102 , or 100, times more acidic than coffee.

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Let’s Review

Lemon juice has a pH of 2.2. Is it an acid or a base?

Detergents such as Tide have a pH of about 10. Is Tide an acid or a base?

Seawater has a pH of 8.2. Is seawater an acid or a base?

The inside of your mouth has a pH of 7. Is it an acid or a base?

409 cleaner contains ammonia that has a pH of 12. What will 409 do to red litmus paper?

A soft drink has a pH of 3.2. What will it do to a piece of red litmus paper?

You can find pH from the concentration of a strong acid.

pH is the negative power of 10 that is used to describe the concentration of H3O+ ions.

The concentration of H3O+ in pure water is 1 x 10-7.

The pH of pure water = 7

Determining pH

The concentration of H3O+ ions in a solution of a strong acid is the same as the concentration of the acid.

Determine the pH of a 0.0001 M (Molar) solution of the strong acid HCl.

concentration of H3O+ ions = concentration of HCl

concentration of H3O+ ions = 0.0001 M = 1 x 10-4

M

pH = -(-4) = 4

Determining pH