Acids and Bases

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Acids and Bases

What are acids and bases?

• Acids and Bases are one way of classifying matter through its properties.

Properties of Acids

–Taste sour–Change blue litmus paper to red color–pH less than 7–Reacts with carbonates and bicarbonates

forming CO2 gas –React with metals to form a salt

compound and H2 gas (pop!)–electrolyte

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Reacts with carbonates and bicarbonates forming CO2 gas

MgCO3(s) + 2HCl(aq) → MgCl2(aq) + H2O(l) + CO2(g)

carbonate acid salt water carbon dioxide

*Remember that you can test for CO2 using a burning splint. The CO2 gas will put out the flame of the burning splint.

React with metals to form a salt compound and hydrogen gas (pop!)

2 HCl + Mg MgCl2 + H2

acid metal salt hydrogen gas

*Remember that you can test for H2 using a burning splint. The H2 gas will make a popping sound and put out the flame of the burning splint.

Electrolytes - chemicals that dissociate when in water

Dissolve Dissociate

Name of acid Chemical formula Common use or location

Hydrochloric acid HCl Gastric juice

Sulfuric acid H2SO4 Car batteries

Nitric acid HNO3 fertilizer

Carbonic acid H2CO3 Soft drinks

Uric acid C5H4N4O3 urine

Ascorbic acid (Vitamin C) C6H8O6 fruit

Citric acid C6H8O7 Citrus fruit

Acetic acid HC2H3O2 vinegar

Tartaric acid C4H6O6 grapes

Properties of bases

–Taste bitter–Feel slippery–Change red litmus paper to blue

color–pH greater than 7–electrolyte

Neutral solutions

Substances that are neither acids nor bases

• do not change the color of red or blue litmus paper

• pH equals 7• nonelectrolytes

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Arrhenius Definition of AcidsArrhenius acids - give (donate)

hydrogen ions (H+) in aqueous solution. *an H+ ion is a proton

HCl + H2O H3O+ + Cl-

Example:

What happened to the H of HCl?

Which substance is the acid: HCl or H2O?

How do you know?

Arrhenius bases – give (donate) hydroxide ions (OH) -1 in aqueous solution.

NaOH (aq) Na+ + (OH)-

Example:

What happened to NaOH when it was added to water?

Why is NaOH classified as an Arrhenius base?

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PracticeUsing the Arrhenius definition, classify the

following as an acid or a base in water1. HI

2. KOH

3. HNO3

4. Ca(OH)2

5. H2SO4

6. Mg(OH)2

Acid, in water HI H+ + I-

Acid, in water HNO3 H+ + NO3-

Base, in water KOH K+ + OH-

Base, in water Ca(OH)2 Ca+2 + 2OH-

Base, in water Mg(OH)2 Mg+2 + 2OH-

Acid, in water H2SO4 2H+ + SO4-2

Arrhenius definition of acids and bases is limited.

Brönsted-Lowry Definition of Acids and Bases

Acids donate a proton or H+ (proton donor)

Bases takes in a proton or H+ (proton acceptor)

NH3 is accepting an H+ so it is a B-L base.

Brönsted-Lowry Definition of Acids and Bases

• A conjugate base is the remainder of the original acid, after it donates its hydrogen ion

• A conjugate acid is the particle formed when the original base gains a hydrogen ion

For example:

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conjugate conjugate

Leftovers from acid

Base that has gained an H+

Practice: Brönsted-Lowry Acids and Bases

Identify the B-L acid (a), conjugate base (c.b.), B-L base (b), and conjugate acid (c.a.)

1. HCl + H2O ↔ H3O+ + Cl-

2. HNO2 + H2O ↔ H3O+ + NO2-

3. SO3-2 + H2O ↔ HSO3

- + OH-

Ans: acid + base ↔ c.a. + c.b

Ans: acid + base ↔ c.a. + c.b

Ans: base + acid ↔ c.a. + c.b

Review

In a B-L acid-base reaction:• What happens to an acid?

• What happens to the base?

• What is a conjugate base?

• What is a conjugate acid?

Lost the proton (H+)

gained the proton (H+)

Acid without the proton (H+)

Base with the proton (H+)

More Practice: Brönsted-Lowry Acids and Bases

Identify the acid, conjugate base (c.b.), base, and conjugate acid (c.a.)

1. HC2H3O2 + H2O ↔ H3O+ + C2H3O2-

2. CO32- + H2O ↔ HCO3

- + OH-

3. NH4+ + H2O ↔ NH3

+ H3O+

Ans: acid + base ↔ c.a. + c.b

Ans: base + acid ↔ c.a. + c.b

Ans: acid + base ↔ c.b. + c.a

The pH concept

Aci

dic

Alk

alin

e (

basi

c)

Neutral

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pH (8:53)

formula: pH = -log[H+] [H+] = concentration of H+ ions

Example 1: What is the pH of a solution with [H+] = 1 x 10-3 M?

formula: pH = -log[H+] where [H+] = concentration of H+ ions

Example 2: What is the pH of a solution with [H+] = 1 x 10-8 M?

The pH concept

1. [H+] = 0.01 M

2. H+] = 0.0001 M

3. [H+] = 10-7 M

4. [H+] = 0.015 M

5. [H+] = 3.2 x 10-10 M

6. [H+] = 6.5 x 10-4 M

7. [H+] = 4.5 x 10-8 M

pH = 2, acid

Practice: Find the pH of the following solutions and state whether the solution is an acid, base or neutral.

pH = 4, acid

pH = 1.8, acid

pH = 9.5, base

pH = 3.2, acid

pH = 7, neutralpH = 7.3, base

pH scale

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[H+][OH-]

14

0

• What is the difference in the dissociation of strong and weak acids?

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Strong Acids and Bases• Strong acids completely dissociate and release

[H+] ions. HCl H+ + Cl-

• Strong bases completely dissociate and release [OH-] ions.

NaOH Na+ + OH-

These are the ONLY strong acids:HCl, HBr, HI, HNO3, HClO4, H2SO4

Some strong bases – NaOH, KOH, LiOH

Particle diagrams

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strong acid – complete dissociation

weak acid – partial dissociation

Comparison between Solutions of Strong and Weak Acids• Two solutions are represented by the diagram below. Which

diagram illustrates a solution of a weak acid? How do you know?

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A B

H+ concentration of Strong and Weak Acids

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How is the pH related to the H+ ion concentration of weak and strong acids?

Concentrated vs. Dilute• Concentrated acids and bases have a

relatively large # of moles (of acid or base) per liter of solution.

• Dilute acids and bases have a relatively small # of moles (of acid or base) per liter of solution.

• 10.0 M HF is more concentrated than 2.0 M HF.

• 2.0 M KOH is more dilute than 10.0 M KOH. 34

Two acids, HCl and HC2H3O2 are both 0.10 M. Which of the two has a higher pH and why?

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H+ Concentration of Strong and Weak Acids

A B

Acid Base Concentration

Molarity- The number of moles of solute dissolved in 1.00 L of solution Molarity (M) = Moles of solute Liter of solution

Example: What is the molarity if 2.0 moles of hydrochloric acid are added to 5.0 L of solution?

M = 2.0 mol = 0.40 M

5.0 L

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Diluting Solutions

• Diluting Solutions: V1M1 = V2M2

• Example: What volume of 2.0 M H2SO4 would you need to prepare 100. mL of 0.40 M H2SO4?

V1 = x

M1 = 2.0M (x)(2.0) = (100)(0.40)

V2 = 100.ml x = 20 mL

M2 = 0.40 M

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Indicators• Chemicals that change color in the presence of

an acid or a base• Used to determine the pH of a solution• Examples: litmus paper (red and blue), pH

paper, phenolphthalein, red cabbage juice

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Indicators

Acid Vocabulary Binary acid – acid that contains only H and one other type of atom

Ex. HBr, H2S

Ternary acid – acid that contains H and a polyatomic ion

Ex. H2SO4

Monoprotic acid – acid that only has one H atomEx. HBr, HI

Polyprotic acid – acid that has more than one H atomEx. H2S, H3PO4

*a hydrogen ion, H+, is a proton

Anion Ending Acid Name

-ide hydro-(stem)-ic acid

-ate (stem)-ic acid

-ite (stem)-ous acid

Naming Acids (stop at 5:47)

No Oxygen

w/Oxygen

Examples: HCl – hydrochloric acid HClO3 – chloric acid

HClO2 – chlorous acid

binary

ternary

Naming Acids

h yd ro - p re fix-ic e n d ing

2 e le m e n ts

-a te e nd ingb e com es-ic e nd ing

-ite e nd ingb e com es

-o us e nd ing

n o h yd ro- p re fix

3 o r m o re e le m e n ts (w ith o xyg e n)

AC ID Ss ta rt w ith 'H '

binary

PracticeName the following

acids:1. HI

2. HF

3. H2SO4

4. H2SO3

5. H2CO2

Write the chemical formula:

6. Hydrobromic acid

7. Hydrosulfuric acid

8. Acetic acid

9. Phosphoric acid

10. Nitrous acid

Hydroiodic acid

Hydrofluoric acid

sulfuric acid

sulfurous acid

carbonic acid

H2S

HC2H3O2

H3PO4

HNO2

HBr

Symbol, ox #, criss-cross

Hydroxides (OH-)

NaOH sodium hydroxide

Mg(OH)2 magnesium hydroxide

Al(OH)3 aluminum hydroxide

Base Nomenclature

Ammonia - NH3 is a common base found in household glass cleaners.

Most bases are named the same as any other ionic compound, for example:

Writing formulas for bases

Just like all ionic compounds, write the symbol for each ion, its oxidation number, and then criss-cross to get the subscripts.

Example: potassium hydroxide

K+1 (OH)-1

KOH or K(OH)

Practice writing formulas for bases

1. Zinc hydroxide

2. Iron (II) hydroxide

3. Calcium hydroxide

4. Lithium hydroxide

Neutralization

• one type of double replacement reaction• Reactants are acid and base, products are

salt and water

• Acid + Base Salt + water

HCl + NaOH NaCl + H2O

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Titration (6:52)

• A controlled acid-base neutralization reaction• The process of finding the concentration of an

unknown solution by using a certain volume of a known concentration solution.

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• This solution is also called the analyte or titer

• Unknown concentration

known concentration

End point of a titration

• The point where neutralization is achieved• Occurs just before the indicator has changed

color• DETERMINED BY OBSERVATION, DURING THE

TITRATION EXPERIMENT

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Equivalence Point

• the stoichiometric end point of a titration

• when moles of H+ from acid = moles of OH- from base

• DETERMINED FROM THE DATA COLLECTED IN THE TITRATION EXPERIMENT

Neutralization Problems-

(#H+)MAVA = MBVB(#OH-)

• #H+ = #H in chemical formula• MA = molarity of acid

• VA = volume of acid

• MB = molarity of base

• VB = volume of base• #OH- = #OH in chemical formula

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Practice: Neutralization Problem

(#H+)MAVA = MBVB(#OH-)

When 45.0 mL of 3.00 M HBr is added to 80.0 mL of Ca(OH)2 What is the molarity of the Ca(OH)2 that was neutralized?

#H+ = MA =

VA =

MB =

VB =

#OH- =

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Practice: Neutralization Problem(#H+)MAVA = MBVB(#OH-)

• In a titration experiment, if 65.0 mL of an HCl solution reacts with 47.2 mL of a 0.65-M NaOH solution, what is the concentration of the HCl solution?

#H+ = MA =

VA =

MB =

VB =

#OH- =

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Ion Stoichiometry : )

H2SO4 + 2NaOH Na2SO4 + 2H2O

240 grams of NaOH react with sulfuric acid. How many moles of H+ ions are consumed?