acids and bases fyi… what is the name of the strong acid found in your stomach?

Acids and bases

FYI…

What is the name of the strong acid found in your stomach?

Homework

• Read Section 15-1 & 15-2 (pg. 453-462)in your chemistry textbook

• Complete the guided notes sheets (only pages 1 and 2) that connect to Chapter 15 Section 1 by…

What is an acid? What is a base?

• They are just groups of chemicals that share certain physical and chemical properties

• These properties, like properties of any chemical group, come from the structure and composition of their molecules

Think of some names of common acids

Vinegar is dilute acetic acid

Yogurt contains lactic acid

Soda Pop contains carbonic acid

Lemons and oranges contain citric acid

The word acid comes from the Latin word acidus which means

sour or tart

Acids…

• Feel like water on the skin

• Sour taste

• Produce CO2 when combined with carbonates

• Electrolytes (conduct electricity because they ionize in water)

Acids

• Change color of acid-base indicators (blue litmus paper turns red in acid)

• Neutralized by bases (acid no longer has its characteristic properties water plus a salt)

What are some common bases?

Ammonia

Drano contains sodium hydroxide

Milk of magnesia contains magnesium hydroxide

Bases…

• Feel slippery on the skin

• Bitter taste (Soapy water)

• Electrolytes too(conduct electricity because they ionize in water)

Bases

• Change color of acid base indicators (red litmus paper turns blue in base and phenolphtalein turns pink)

• Neutralized by acids (base no longer has its characteristic properties water plus salt)

We have characterized bases… but… What are they??

Some definitions

Categories of Acids

• Binary acids

• Oxy acids

• Carboxylic acids

• The categories are based on structure and composition

Binary Acids

• Contain H+ and one other element

• Other element usually from group 16 or 17

• HCl and HBr are strong binary acids

• HF and H2S are weak binary acids

Oxy Acids

• Contain H+ and O- and one other element

• Acidic hydrogen is attached to oxygen

• H2SO4 called King of Chemicals

• Strong H2SO4, HNO3, HClO4

• Most others are weak

Naming Acids

• Logical system using roots, prefixes and

• suffixes

Naming Acids

Anion(examples)

-----ide(chloride, Cl-)

-----ate(chlorate, ClO3

-)-----ite(chlorite, ClO2

-)

add H+ add H+ add H+

Acid(examples)

Hydro---ic acid(hydrochloric acid,HCl)

-----ic acid(chloric acid,HClO3)

-----ous acid(chlorous acid,HClO2)

Common strong acids Common weak acids

HCI hydrochloric acid HCH3O2 acetic acid

HBr hydrobromic acid HF hydrofluoric acid

HI hydroiodic acid HCIO hypochlorous acid

HNO3 nitric acid HNO2 nitrous acid

H2SO4 sulfuric acid HCN hydrocyanic acid

HCIO4 perchloric acid

Common strong bases Common weak bases

NaOH sodium hydroxide NH3 ammonia

Ca(OH)2 calcium hydroxide CO32- carbonate ion

CaO calcium oxide PO43- phosphate ion

KOH potassium hydroxide

Sulfuric Acid• Discovered by • Abu Musa Jabir ibn

Hayyan: also known as Geber in the 8th century

• Reaction with water is highly exothermic

• Part of acid rain made from oxidation of SO2

• In the presence of water

• Found in planet Venus upper atmosphere

• Very commononly used in industrial processes

Nitric Acid

•  used to make explosives, plastics and medicinal drugs

• It is mainly used in the production of fertilizers for plants

• Stains proteins yellow, even human skin

Nitric Acid reacting with Copper

Hydrochloric Acid

• Industrially useful for “pickling” iron and steel

• General cleaning agent• Can be purchased as

Muriatic acid• Pool maintenance…

Acid Strength and Concentration are not the same thing…

Acid strength…

• Strong acids readily transfer H+ ions to H2O to form H3O+ions

• Strong acids readily form electrolytes

• Weak acids do not readily transfer H+ ions– Only a small amount will ionize

The Arrhenius Definition

Svante Arrhenius

1859-1927

Arrhenius Definition

• Understood in terms of the ions they produce when dissolved in water

Arrhenius Definition

• An acid is a substance that dissociates in water to produce hydrogen ions

• Acids= H+

Arrhenius Definition

• A base is a substance that dissociates in water to produce hydroxide ions

• Base = OH-

Arrhenius Definition

• Examples

• HNO3(aq) H+(aq) + NO3-(aq) = acid

• NaOH(aq)Na+(aq) + OH-(aq) = base

Arrhenius Definition

• Helps understand neutralization

• H+ + OH- H2O• HCl(aq) + NaOH(aq) NaCl(aq) +H2O

What kind of reaction is this?

Arrhenius Definition

• Problem with Arrhenius definition– restricts acids/bases to aqueous solutions– Simplifies what happens (acids do not have

ionic bond)– Sometimes substances act like acids or bases

when they are not aqueous– Therefore…

Bronsted-Lowry Definition

A second acid/base definition

Johannes Bronsted (1879-1947)

Thomas Lowry (1874- 1936)

Bronsted-Lowry Definition

• Definition is independent of water

• Focuses solely on H+ ions

• An acid is any substance that can donate H+ ions

• A base is any substance that can accept H+ ions– Or a base is a proton acceptor.

An H+ ion is a PROTON!

Sometimes we say “proton” instead of “hydrogen ion”. So an acid is a proton donor and a base

is a proton acceptor.

Does H+ ion really exist in aqueous solutions?

• NO! It is a convenient simplification.

• The hydrogen ion, how ever is strongly attracted to the electrons in surrounding water molecules

• H+ + H2O H3O+

• H3O+ = hydronium ion

Example

• HCl(g) + H2O(l) H3O+(aq) + Cl(aq)

• Not

• HCl(g) + H2O(l) H+(aq) + Cl-(aq) +H2O

• Which reactants are Bronsted-Lowry acids and bases? – The resulting solution is still acidic because of

the H3O+ or H+ ions

Example

• NH3(g) + H2O(l)NH4+(aq) + OH-(aq)

• Which reactants are Bronsted-Lowry acids and bases? – This resulting solution is still basic because of

the OH- ion.

Lewis Acids and Bases

• Both Arrhenius and Bronsted –Lowry definitions assumes that the acid contains or produces hydrogen ions

• Lewis definition does not make that assumption• Definition = A Lewis Acid is an atom, ion or

molecule that accepts an electron pair to form a covalent bond.

• Lewis definition is the most broad and used most widely in organic chemistry

Lewis Acids & Bases

• Lewis Acid…

• BF3 (aq) + F- BF-4(aq)

Lewis Bases

• Definition = A Lewis base is an atom, ion or molecule that donates an electron pair to form a covalent bond

Acid & Base Summary…

Category Acid Base

Arrhenius H+ or H3O producer OH- producer

Bronsted-Lowry Proton (H+) donor Proton (H+) acceptor

Lewis Acid Electron pair acceptor Electron pair donor

Conjugate acid-base pairs

• Conjugate means coupled or joined together

• We can write acid-base reactions as reversible reactions

This flow chart represents a cell’s metabolic pathways and show the first two steps in the breakdown (catabolism) of glucose.

These chemical reactions are reversible like many other chemical reactions. Acid base reactions are often times reversible too….

Acids Base reactions are often used to help maintain Biological Homeostasis…

• Buffers resist changes to the pH of a solution when H+ or OH- is added to the solution.– Buffers accept hydrogen ions from the

solution when they are in excess and donate hydrogen ions when they have been depleted.

• The next slide explain more about how buffers work in the human blood…

• Buffers typically consist of a weak acid and its corresponding base. – One important buffer in human blood and other

biological solutions is carbonic acid (H2CO3)

– The chemical equilibrium between carbonic acid and bicarbonate ion acts as a pH regulator.

– The equilibrium shifts left or right as other metabolic processes add or remove H+ from the solution.

Conjugate acid-base pairs

• We can write acid-base reactions as reversible reactions

• NH3 (g) + H2O(l) NH4+ (aq) + OH – (aq)

• The difference between an acid and a base can be as simple as one hydrogen ion

Conjugate acid-base pairs

• In the forward reaction ()

• NH3 gains a proton = base

• H2O loses a proton = acid

• NH3(g) + H2O(l) NH4+ (aq) +OH-(aq)

Conjugate acid-base pairs

• In the reverse reaction ()

• NH4+ loses a proton = conjugate acid

• OH- gains a proton = conjugate base

• NH3(g) + H2O(l) NH4+ (aq) +OH-(aq)

Conjugate acid-base pairs

• Forward reaction• NH3 gains a proton-

base• H2O loses a proton-

acid

• Reverse reaction • NH4+ loses a proton-

conjugate acid• OH- gains a proton-

conjugate base

Conjugate acid-base pairs

• NH3(g) + H2O(l) NH4+ (aq) +OH-(aq)

• NH3 and NH4+ are called a conjugate acid-base pair.

• See page 471 (table15-6) for a list of conjugate acids and bases.

Conjugate aids and bases…

• Strong acids, ones that easily ionize, have weak conjugate bases

• The same is true for strong bases and their conjugate acid pair

• See page 471 table 15-6 for additional info…

Amphoteric- a substance that can act either as an acid or a base,

depending on the circumstances (water is a perfect example)