acids and bases. characteristics of acids sour taste (aqueous solutions) change the color of...

Acids and Bases

Characteristics of Acids

Sour taste (aqueous solutions) Change the color of indicators

pH paper: reds and oranges

Litmus paper: red

Clear in phenolphthalein

Bromthymol blue - yellow

Phenol red-yellow

Some react with active metals and release hydrogen gas Acids react with bases to form salts (neutralization

reactions) Acids conduct electricity. pH 1-7 Strong and weak acids

Uses of Acids Acetic Acid (CH3COOH)= Vinegar

Citric Acid (C6H8O7) = lemons, limes, & oranges. It is in many sour candies such as lemonhead & sour patch.

Ascorbic acid (C6H8O6) (= Vitamin C which your body needs to function.

Sulfuric acid (H2SO4) is used in the production of fertilizers, steel, paints, and plastics.

Acetylsalicylic acid ((C9H8O4)-aspirin

HCl- used in our stomach to digest food.

Characteristics of Bases Taste bitter (aqueous solutions) Change the colors of indicators

pH paper –green and blue Litmus paper blue Phenolphthalein-pink Bromthymol blue-blue Phenol red-pink

Dilute aqueous solutions feel slippery Bases react with acids to form salts (neutralization

reactions) Bases conduct electricity. pH 8-14

Uses of bases

Bases give soaps, ammonia, and many other cleaning products some of their useful properties.

The OH- ions interact strongly with certain substances, such as dirt and grease.

Chalk and oven cleaner are examples of familiar products that contain bases.

Your blood is a slightly basic solution (7.4)

Common Acids

Fruit Juices Sulfuric acid

Used in petroleum refineries and the manufacture of fertilizer. Dehydrates water from compounds.

Nitric acid Stains proteins yellow, used in explosives.

Phosphoric acid Used in the manufacture of fertilizer and animal feed.

Hydrochloric acid Removes impurities from metal, digests food in stomach

Acetic acid Used to make vinegar and as a fungicide.

Carbonic acid Found in the blood as a buffer (maintains pH)

Common BasesMilk of Magnesia

Neutralize acid in the stomach and maintain pH

Blood Transports oxygen and nutrients

Drain Cleaner Loosen debris and dissolve substances

Bleach Cleaner

Ammonia Cleaner *Using ammonia and bleach together releases toxic

fumes!

3 Types of Acids and Bases

Arrhenius Model Acids-contain H and

donate and H+ to solution.

Bases-contain OH and donate OH- to solution.

Examples Acids: HF, HI, HCl, H2O,

HBr, H2SO4, H3PO4

Bases: NaOH, Ca(OH)2, KOH, H2O

Bronsted-Lowry Acids- compounds that

donate a proton (H+)

Bases-compounds that accept a proton (H+)

Examples Acids: HCl, HF, HI

Bases: NH3, H2O

Lewis: bases donate electron pair (NH3) and acids accept electron pairs (don’t need to have hydrogen!

Misc.

Acidic solutions Solutions with more H+ than OH-

Basic solutions Solutions with more OH- than H+

Conjugate acid The species that results when a base accepts a proton

Conjugate base The species that results when an acid loses a proton.

Amphoteric A substance that acts as both an acid or a base (water).

Conjugate Acid/Base Pairs

Acid + Base Conjugate Acid + Conjugate Base

H2SO4 + H2O H3O+ + HSO4-

H3PO4 + H2O H3O+ + H2PO4

-

Write the acid….+ water H3O+ + conjugate base

Strong Vs. Weak Strong

The entire sample of Strong acids and bases completely dissociate when dissolved. Ex. Hydrobromic, hydrochloric, nitric….

Weak Weak acids and bases do not completely dissociate when

dissolved. Some of the sample is still together as an entire compound. (hydrosulfuric, hypochlorous, carbonic….

*We will be working with strong acids and bases in problem sets.

Ionization Constant-to what degree will a substance produce ions in water?

Ka

[products]/[reactants]

DO NOT WRITE LIQUIDS!

The smaller the number the WEAKER the acid.

Kb

[products]/[reactants]

DO NOT WRITE LIQUIDS!

The smaller the number the WEAKER the base.

pH Scale0-14 Based on a Scale of 10

A change from pH 3 to 2 means 10X more H3O+

A change from pH 3 to 1 means 100x more H3O+

“power of Hydrogen” [H3O+] of 100 to 10-14

Acids 0-7Neutral 7Bases 7-14pH = - log [H3O+] pOH = - log [OH-]

Ionization of Water

[H3O+]= hydronium ions[OH-] = hydroxide ions

H2O(l) + H2O(l) H3O+ + OH-

Water ionizes, therefore it has a pH

pH = - log [H3O+]

At 25○C [H3O+] = 1.0 x 10-7 MAt 25 ○ C [OH-] = 1.0 x 10-7 M

[H3O+][OH-] = 1.0 x 10-14 M

Reactions with Acids and Bases A reaction between an acid and a base is called

neutralization. An acid-base mixture is not as acidic or basic as the individual starting solutions.

Neutralization reactions make SALTS

Types of Salts

AcidicStrong Acid + Weak Base

Turn litmus paper red

BasicWeak Acid + Strong Base

Turn litmus paper blue

NeutralStrong Acid + Strong Base

Turn red litmus red, and blue litmus blue

[H3O+][OH-] = 1.0 x 10-14 M

Acidic solutions [H3O+] > [OH-]

A pH of 4 means that [H3O+] = 1.0 x 10-4 (more)

This means the [OH-] = 1.0 x 10-10 (less)

Basic solutions [H3O+] < [OH-]

A pH of 10 means that [H3O+] = 1.0 x 10-10 (less)

This means the [OH-] = 1.0 x 10-4 (more)

Formulas to Remember

[H3O+][OH-] = 1.0 x 10-14 M

pH = - log [H3O+]

[H3O+] = antilog (-pH)

Also written as [H3O+] = 10-ph

Calculating pH from [H3O+]

What is the pH of a 1.0 x 10-3 M NaOH solution? NaOH Na+ + OH-

1.0 x 10-3 M NaOH = 1.0 x 10-3 M OH-

[H3O+]= 1.0 x 10-14 M = 1.0 x 10-11 M 1.0 x 10 -3 M

pH = - log [ 1.0 x 10-11] pH = 11

Conversely then, the pOH = 3

Calculating Concentrations from pH and pOH pH = -log [H3O+]

Log [H3O+] = -pH

[H3O+] = antilog (-pH)

[H3O+] = 10-pH

Determine the [H3O+] of an aqueous solution that has a pH of 4.0.

[H3O+] = 10-4 which is the same as 1 x 10-4M

Calculating [H3O+] from [OH-]

NaOH Na+ + OH-

Strong Base= completely dissociates

If this is a 1.0 x 10-2 M solution then…

1.0 x 10-2 mol NaOH x 1 mol OH- = 1.0 x 10-2 mol OH

L solution 1 mol NaOH L solution

Because [H3O+][OH-] = 1.0 x 10-14 M

[H3O+]= 1.0 x 10-14 M = 1.0 x 10-12 M 1.0 x 10 -2 M

Calculating [OH-] from [H3O+]

HCl H+ + Cl-

Strong Acid= completely dissociates If this is a 2.0 x 10-4 M solution then…

2.0 x 10-4 mol HCl x 1 mol H+ = 2.0 x 10-4 mol H

L solution 1 mol HCl L solution

Because [H3O+][OH-] = 1.0 x 10-14 M

[OH-]= 1.0 x 10-14 M = 5.0 x 10-10

M 2.0 x 10 -4 M

Comparisons

Neutral [H3O+] = [OH-]

pH = pOH

[H3O+] = [OH-]= 1.0 x 10-7

pH = pOH = 7

Acidic [H3O+] > [OH-]

pH<pOH

[H3O+] > 1.0 x 10-7

[OH-] < 1.0 x 10-7

pH< 7

pOH>7

Basic [H3O+] < [OH-]

pH>pOH

[H3O+] <1.0 x 10-7

[OH-] >1.0 x 10-7

pH>7

pOH<7

Titration:

A laboratory method for determining the concentration of an unknown acid or base using a neutralization reaction.

A standard solution,(a solution of known concentration), is used.

Equivalence Point

The point at which there are stoichiometrically equivalent amounts of acid and base.

[H+] = [OH-]

Buret

Valve

Titration

Acid with Phenolphthalein

End-Point

IndicatorsIndicators are chosen, such that they change colors at the range of the pH of interest.

The solution itself at the end-point may be:Basic, if the reaction involves a strong base and

a weak acid.

Neutral, if the reaction involves a strong acid and a strong base.

Acidic, if the reaction involves a strong acid and a weak base.

Methods of Solving Titration Problems:

a) using stoichiometry

b) using the titration formula aMaVa=bMbVb.

What is the concentration of HCl if 30.0 mL of 0.10 M NaOH neutralizes 50.0mL HCl?

NaOH + HCl H2O + NaCl

Hint: Use aMaVa=bMbVb

Ma=

How many moles of HCl were used?

Hint: #moles= MaVa , but convert the volume to L( 50mL=0.05L).

A 20.0 mL solution of Sr(OH)2 is neutralized after 25.0 mL of standard 0.05 M HCl is added. What is the concentration of Sr(OH)2?

2 HCl + Sr(OH)2 2 H2O + SrCl2

How many mL of 0.20 M H3PO4 are needed to neutralize 55.0 mL of a 0.10 M solution of NaOH?

What volume of 0.20M Ca(OH)2 will neutralize 45.0 mL of a 1M solution of HClO3?