Acids and Bases and pH
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Acids and Bases and pH

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Acids and Bases and pH




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Presentation on theme: "Acids and Bases and pH"— Presentation transcript:

Slide1

Acids and Bases and pH

Slide2

Chemistry

Acids and Bases

Properties and pH

Slide3

Chemical Warfare!

Slide4

What is an Acid?

3 Major Definitions: Arrhenius, Bronsted-Lowry, and Lewis.

Arrhenius and Bronsted-Lowry say an acid is:

A proton donor

What is a proton?

A proton = H

+

H

+

= H

3

O

+

Slide5

Acid and Base Strength

Acids and bases are considered “strong” or “weak” depending on how much they dissociateThe more something dissociate, the stronger acid or base it is.This means we are looking at the amount of H+ or OH- is in the solution

Slide6

Ionization of HCl and formation of hydronium ion, H3O+

H

2O + HCl 

H3O+ + Cl-

Proton donor

Proton

acceptor

Slide7

Strong Acids vs. Weak Acids

Strong acids are assumed to be 100% disassociated in solution (good proton donors). Are Strong Electrolytes

Weak acids are usually less than 5% disassociated in solution (poor proton donors). Are Weak Electrolytes.

HCl

H2SO4

HNO3

H3PO4

HC

2

H

3

O

2

Slide8

Strong Acid Dissociation

Slide9

Weak Acid Dissociation

Slide10

Arrhenius & Bronsted-Lowry Acids= Proton Donors

Monoprotic acids

Diprotic acids

Triprotic acids

HCl

HC2H3O2

HNO3

H2SO4

H2CO3

H

3

PO

4

Slide11

Properties of Acids

Acids taste sour

Acids effect indicators

Blue litmus turns red

Methyl orange turns red

Acids have a pH lower than 7

Acids are proton (hydrogen ion, H

+

) donors

Acids react with active metals, produce H

2

Acids react with carbonates, produce CO

2

Acids neutralize bases

Slide12

Sulfuric Acid

Highest volume production of any chemical in the U.S. Used in the production of paper Used in production of fertilizers Used in petroleum refining

Slide13

Nitric Acid

Used in the production of fertilizers Used in the production of explosives Nitric acid is a volatile acid – its reactive components evaporate easily Stains proteins (including skin!)

Slide14

Hydrochloric Acid

Used in the pickling of steel Used to purify magnesium from sea water Part of gastric juice, it aids in the digestion of protein Sold commercially as “Muriatic acid”

Slide15

Phosphoric Acid

A flavoring agent in sodas Used in the manufacture of detergents Used in the manufacture of fertilizers Not a common laboratory reagent

Slide16

Acetic Acid

Used in the manufacture of plastics Used in making pharmaceuticals Acetic acid is the acid present in vinegar

Slide17

Acids Effect Indicators

Blue litmus paper turns red in contact with an acid.

Slide18

Acids Have a pH less than 7

Slide19

Acids React with Active Metals

Acids react with active metals to form salts and hydrogen gas.

Mg + 2HCl  MgCl2 + H2(g)

Acids did not react with Copper, because copper is not an

Active Metal

Slide20

Acids React with Carbonates

2HC

2H3O2 + Na2CO3

2 NaC

2

H

3

O

2

+ H

2

O + CO

2

Slide21

Effects of Acid Rain on Marble(calcium carbonate)

George Washington:

BEFORE

George Washington:

AFTER

Slide22

What is a Base?

3 Major Definitions: Arrhenius, Bronsted-Lowry, and Lewis.

Arrhenius Base increases OH

-

concentration when in solution.

NaOH

when disassociated produces:

Na

+

& OH

-

Bronsted-Lowry Bases are proton (H

+

) acceptors.

NH

3

+

HCl

 NH

4

+

+ Cl

-

An Arrhenius base is always a B-L Base, but a B-L base is not always an Arrhenius base.

Slide23

Properties of Bases

Bases taste bitter

Bases effect indicators

Red litmus turns blue

Phenolphthalein turns purple

Bases have a pH greater than 7

Bases are proton (hydrogen ion, H

+

) acceptors

Solutions of bases feel slippery

Bases neutralize acids

Slide24

Examples of Bases

Sodium hydroxide (lye), NaOH Potassium hydroxide, KOH Magnesium hydroxide, Mg(OH)2 Calcium hydroxide (lime), Ca(OH)2

Slide25

Strong Bases vs. Weak Bases

Strong bases are assumed to be 100% disassociated in solution. Are strong electrolytes!

Weak acids are usually less than 5% disassociated in solution. Are Weak electrolytes!

NaOH

Ca(OH) 2

Cu(OH)2

NH

3

Slide26

Strong Base Dissociation

NaOH

Na

+

OH

-

Slide27

Weak Acid Dissociation

OH

-

AgOH

Ag+

AgOH

Slide28

Bases Effect Indicators

Red litmus paper turns blue in contact with a base.

Phenolphthalein turns purple in a base.

Slide29

Bases have a pH greater than 7

Slide30

Is H2O an acid or base?

HCl +

H

2

O

 H

3

O

+

+ Cl

-

H

2

O is an base! = proton acceptor

NH

3

+ H

2

O  NH

4

+

+ OH

-

H

2

O is an acid! = proton donor

H

2

O can be either. This is called

Amphoteric = can act like an acid or base.

Slide31

Ion Concentration in Water

Slide32

pH- what is it?

pH is a measure of the H

+

or H

3

O

+

concentration.

The higher the concentration of H

+

or H

3

O

+

, the lower the pH.

Acids have higher [H

3

O

+

], than pure water

pH range of an acid is 0 - 6.99.

pH of pure water is 7

Slide33

pOH- what is it?

pOH is a measure of the OH

-

concentration.

The higher the OH

-

concentration, the lower pOH.

Bases have higher OH

-

concentrations than pure water.

pH and pOH are exact opposites!

In a solution:

when the [H

3

O

+

] increases, [OH

-

] decreases

when pH increases, pOH decreases

Slide34

Self-Ionization of Water

H

2O + H2O  H3O+ + OH-

pH explained

Slide35

H+, OH-, and pH

Slide36

pH Scale

Slide37

How Do You Determine?

Described by an ionization equation:Each acid and base will have either a high or low percent ionizationi.e. a high or low amount of the solution which dissociates into ionsThe higher the percent ionization the stronger the acid

HCl

(

aq

)→ [H]

+

+ [

Cl

]

Slide38

pH

The pH is defined according to the following formula:pH = -log[H+]and [H+]=10-pHwhere [H+] represents the concentration of hydrogen ions in mol/L

Slide39

pOH

The pOH is defined according to the following formula:pOH = -log[OH-]and [OH-]=10-pOHAlso note that pH + pOH= 14

Slide40

pH and pOH is logarithmic

The pH and pOH scale is logarithmic, just like the Richter scale for earthquakes!So a change of 1 pH means the concentration has changed by a factor of 10!

Slide41

Acid and Base Strength

For

bases

, a

solution with a

pH of 13

is:

10

times more basic than a solution with a

pH of

12

100

times more basic than a solution with a

pH of 11

 

For

acids

,

a

solution with a

pH of 3

is:

10

times more acidic than a

solution

with a

pH of

4

100

times more acidic than a solution with a

pH of

5

Slide42

Measuring pH with wide-range paper

Slide43

Narrow-Range pH Paper

Slide44

How Else Can We Measure Strength?

Scientists use a

pH scale

to represent how acidic or basic a solution is

pH means "power of hydrogen”

Slide45

Practice Problems

What is the pH

of

a 1.2 x 10

-3

HBr

solution

?

What is the

pOH

of a 1.2 x 10

-3

HBr

solution?

Slide46

Practise Problems

What is the [H+] concentration in a solution with a pH of 7?

What is the [OH-] concentration in a solution with a pH of 12?

Slide47

Indicators

The most common method to get an idea about the pH of solution is to use an acid base indicatorAn indicator is a chemical that changes colour depending on the pHA variety of indicators change color at various pH levels

Slide48

Litmus paper

The most common indicator is found on "litmus" paperIt is red below pH 4.5 and blue above pH 8.2

Slide49

Phenolphthalein

Phenolphthalein is a most common liquid indicatorIt is clear below pH 8.5 and pink above pH 8.5

Slide50

Other Indicators

Can also be obtained from many natural sources like strawberries, cabbage, tea and tulips

Slide51

OTHER Tools

Basic indicators only show if a substance is acidic or basic, but not strengthUniversal indicator are a mixture of indicators and can show strength of acid or baseSo can a pH Meter

Slide52

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Slide57