Acids and Bases

Chapter 6.3 & 6.4

Mini-Project

Organize the following formulas into two groups with four formulas in each group:HNO3, NaOH, H2SO4, H2CO3, Ca(OH) 2, KOH, H8PO4, Mg(OH) 2

One way to organize them into groups is:Group One Group TwoHNO3 NaOHH2SO4 Ca(OH) 2

H2CO3 KOHH8PO4 Mg(OH) 2

Group One formulas represent acids.Group Two formulas represent bases.

ACIDS

• Taste sour (lemon, vinegar)

• React with metal (corrosion)

• React with carbonates (makes bubbles of CO2

• Turns blue litmus RED

• In Water forms Hydrogen ION

HCl H+ + Cl-Water

BASES

• Taste Bitter (soap, tonic water)

• Feel Slippery (soap)

• Turns Red Litmus Blue

• In water, forms HYDROXIDE (OH-) ion

• React with Acids to make water

NaOH Na+ + OH-Water

Indicators

• An Indicator is a chemical that turns colors under certain conditions.– Litmus paper is paper with the indicator litmus

on it.– Litmus turns blue when in contact with a base– Litmus turns red when in contact with an acid– There are many different indicators

• Bromthymol blue, universal, malachite green, etc.

Why are Some Solutions Acid & Others Base?

• Acid solutions contain more H+ ions than OH- ions.

• Base solutions contain more OH- ions than H+ ions.

• Water is the standard for Acid/Base and is defined as NEUTRAL

• Water has equal amounts of H+ and OH- ions

Arrhenius Model of Acids/Bases

• Substance is an acid if it contains hydrogen and dissociation causes hydrogen ions to form in solution

• Substance is a base if it contains a hydroxide and dissociates to produce hydroxide ions in solution

Bronsted-Lowry Model

• Acid is a hydrogen ion donor

• Base is a hydrogen ion receptor

• This is a broader definition than Arrhenius model because there are substances that cause donation or reception without having hydrogen in them.

Electrolytes

• Acids and Bases are ELECTROLYTES– They ionize in water– They conduct electricity

Strong vs. Weak•Weak Acids/Bases vs. Strong Acids/Bases

–Strong acids/bases ionize completely

–Weak acids/bases only partly ionize

•Strong Bases are just as dangerous as Strong Acids

–They react with most things they touch

More

• Concentrated vs. Dilute– Concentrated means lots of acid/base in a

little bit of water– Dilute means a little bit of acid/base in a lot of

water

• Concentrated Acids and Bases are VERY Dangerous– They react quickly with many substances

Common Acids

Common Bases

Acid Rain

• Acid rain comes from rain collecting gasses from the air to create acids:– Carbon Dioxide = carbonic acid– Sulfur oxides = sulfuric acid– Nitrogen oxides = nitric acid

• Damages statues, buildings, kills forests, kills fish

pH Scale

pH• pH stands for ‘per hydrion’

– It measures the amount of hydrogen ions in solution– Water is defined as ‘neutral’– Water has one H+ and one OH- equal numbers– The concentration of H+ in water is 1.0 x 10-7

– The pH of water is 7– A lower pH means MORE Hydrogen ions (Acid)

• 10-6 is Larger than 10-7

– A higher pH means LESS hydrogen ions (Base)• 10-8 is Smaller than 10-7

– pH scale is a way of showing this relationship of hydrogen ions

pOH

• In water concentration of H+ = concentration of OH-

– So [H+] = [OH-] = 1.0 x 10-7

– Think about it: • H2O is the same as H-O-H which is H+ + OH-

• So pOH of water is also 7

• pH + pOH always equals 14, so– pH scale goes from 1 to 14

Common Items on the pH Scale

Neutralization Reactions

Acid-Base Reactions

• Neutralization reaction is a reaction between an acid and a base– Makes Water + Salt– Solution becomes Neutral (not acid or base)– NOTE: salt is a ‘category’ of chemicals, not always

sodium chloride

HCl + NaOH H2O + Na+ + Cl-

Acid-Base Reactions

• Mg(OH)2 + 2 HCl → MgCl2 + 2H2O

• Note:– Cation from base (Mg) is combined with anion

from acid (Cl)

– The salt is MgCl2– The H+ and OH- always combine to form

water

Acid-Base Titration

• Acid/Base Titration is the stoichiometry of acid/base reactions.– Titration is a method for determining the

concentration of a solution by using another solution of known concentration

– Uses an INDICATOR to show when the acid/base reaction is complete (neutral)

• Indicator is a chemical that changes color as determined by acid or base conditions

• There are many indicators with different pH points.

Acid/Base Titration Curve

pH Indicators

Name Acid ColorpH Range of

Color ChangeBase Color

Methyl violet Yellow 0.0 - 1.6 Blue

Thymol blue Red 1.2 - 2.8 Yellow

Methyl orange Red 3.2 - 4.4 Yellow

Bromocresol green Yellow 3.8 - 5.4 Blue

Methyl red Red 4.8 - 6.0 Yellow

Litmus Red 5.0 - 8.0 Blue

Bromothymol blue Yellow 6.0 - 7.6 Blue

Thymol blue Yellow 8.0 - 9.6 Blue

Phenolphthalein Colorless 8.2 - 10.0 Pink

Thymolphthalein Colorless 9.4 - 10.6 Blue

Alizarin yellow R Yellow 10.1 - 12.0 Red