2

Unit Vocabulary:

Arrhenius acid Arrhenius base Bronsted-Lowry acid Bronsted-Lowry base Electrolyte

hydronium ion hydroxide ion indicator (acid/base) neutralization pH scale titration

Unit Objectives: Compare and contrast properties of acids, bases, and salts Compare the Arrhenius and Bronsted-Lowry theories of acids and bases Explain and give examples of neutralization reactions Using the titration equation, determine the molarity of an unknown

solution Understand how pH works Using Table M, determine the pH of a given solution

Unit 9: Acids, Bases, & Salts STUDENT VERSION

3

Characteristic Properties of Acids:

acids have a tasteEx: citric acid (fruit), acetic acid (vinegar), carbonic acid (soda),

boric acid used as eye-washing solution

acids BURN skin & EAT HOLES in clothing

Aqueous solutions of acids are (substances that conduct electric current when dissolved in water)

GREATER concentration of IONS = MORE CONDUCTIVE WEAK acids = STRONG acids =

Acids react with BASES to form solutions reaction Called a reaction

Acids react with certain METALS to produce HYDROGEN GAS reaction (Table J) Acid + Metal Anion + Hydrogen Gas

Lesson 1:

4

Acids cause acid-base Ex: litmus paper turns red, phenolphthalein turns from pink to

colorless

have (fall on LOWER end of pH SCALE)

General formula =

7 14 0

5

Characteristic Properties of Bases:

bases have a tasteEx: antacids, soaps, ammonia-based cleaning products

have a feel

CONCENTRATED bases BURN skin & EAT HOLES in clothing

Aqueous solutions of bases are (substances that conduct electric current when dissolved in water)

GREATER concentration of IONS = WEAK bases = STRONG bases =

BASES react with ACIDS to form NEUTRAL solutions reaction Called a reaction

Bases cause acid-base Ex: litmus paper turns blue, phenolphthalein turns from colorless

to pink

Lesson 2:

6

Bases have (fall on HIGHER end of pH SCALE)

General formula =

7 14 0

8

Naming Acids: Table K à acids that and are attached to

a ; in acid’s formula

à acids that & are attached to ain the compound formula—USE TABLE E!

Naming Bases - Table L

7

Characteristic Properties of Salts: Defined as NEUTRAL IONIC SUBSTANCES that have

and ; composed of a positivelycharged metal or polyatomic ion AND a negatively charged nonmetal orpolyatomic ion (with the exception of –OH- which would then make it abase)

Examples of salts à

Salts are and are NEUTRAL

Exception to the rule: NH4Cl is the salt of a weak acid

Electrolyte = A substance that to form and therefore

ACIDS, BASES, & SALTS

ARE ALL ELECTROLYTES (in SOLUTION)

Click on the link below to view the electrolyte animation/tutorial: http://tinyurl.com/6nrhalk

NH4Cl → _____ + Cl- NH4

+ is a weak acid, which means it produces H+ in solution

Lesson 3:

9

An is defined as a substance whose water (aqueous)solution contains or yields as the

in solution

Examples: à H+

(aq) + Cl-(aq)

à 2H+ + SO4-2

GENERAL RULE FOR ACIDS: seen in the formula (H is always the )

++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

** NOT ALL SUBSTANCES THAT CONTAIN HYDROGEN ARE ACIDS. Below is a list of hydrogen compounds that do not dissociate to yield H+ ions.

Non-Examples of Acids: H2O = (neutral) CH4 = methane (natural gas) C6H12O6 = (sugar) H2O2 = hydrogen peroxide NH3 = (a weak BASE!!!)

Acid/Base Theories Lesson 4:

10

THE HYDRONIUM ION: http://www.chemistry.uoguelph.ca/educmat/chm19104/chemtoons/chemtoons2.htm

Let’s recall what happens when a hydrogen atom becomes an ion:

(Lose e-) H H+ + e-

Thus, a POSITIVE HYDROGEN ION is essentially a . When in water, this H+ ION is naturally ATTRACTED to the unshared electrons and slight negative charge of the oxygen in the water. It is believed that the hydrogen ion cannot exist as an isolated particle so what forms is called a

.

According to the Arrhenius theory, the properties of acids are functions of these hydronium (hydrogen) ions. So, because of this, we say that

DIFFERENT TYPES OF ARRHENIUS ACIDS:

Monoprotic acids (1 H+) à acids that produce in solution

Diprotic acids (2 H+) à acids that produce in solution

Triprotic acids (3 H+) à acids that produce in solution

11

An is defined as a substance whose water (aqueous)solution contains or yields/produces as the ONLY NEGATIVE ION when dissolved in water.

GENERAL RULE FOR BASES: contains of the formula

**One Exception to Rule: NH3 = Ammonia

Monohydroxy Bases à produce in aqueous solution

Dihydroxy Bases à produce in aqueous solution

Trihydroxy Bases à produce in aqueous solution

++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

**Not all compounds that contain –OH are bases. For example, ALCOHOLS and ORGANIC ACIDS are NOT BASES. Below is a list of compounds that contain –OH but do not dissociate to yield OH- ions.

Non-Examples of Bases: HOH = water (neutral & amphoteric) CH3OH = methanol (an alcohol) CH3COOH = methanoic acid (an organic acid)

Lesson 5:

12

Alternate Acid-Base Theory (AKA Bronsted-Lowry Theory) This theory explains the behavior of WEAK ACIDS & WEAK BASES

Definitions of the Theory:

BRONSTED-LOWRY ACIDS are the Bronsted-Lowry Acid to Bronsted-Lowry Base

Circle the B-L Acid below:

BRONSTED-LOWRY BASES are the Bronsted-Lowry Base from Bronsted-Lowry Acid

Circle the B-L Base below:

Bronsted-Lowry Conjugate Pairs:

We will use TWO BRACKETS connecting one side of the reaction to the other to represent the (each member within the pair DIFFERS from the other BY MERELY ONE HYDROGEN)

HCl(aq) + H2O(l) H3O+(aq) + Cl-(aq)

Notice: The acid always has one more H than the base!

KEY A = Acid B = Base CA = Conjugate Acid CB = Conjugate Base

H2O + + OH -

Lesson 6:

13

Use brackets and the key from the example on the previous page to indicate the conjugate pairs in the equations below.

Practice Problem 1:

NH3 + HOH NH4+ + OH-

Practice Problem 2:

HCl + HOH Cl- + H3O+

Practice Problem 3:

HI + HOH I- + H3O+

Practice Problem 4:

HNO3 + H2O H3O+ + NO3-

Amphoteric/Amphiprotic = A substance that can ACT LIKE ANACID OR A BASE (can behave as a proton donor or proton acceptor)

Example: WATER is amphoteric (see below)

H2O + H2O H3O+ + OH-

*Amphoteric substances must have at least one HYDROGEN in theirformula

Ex: Which of the following substances is amphoteric?

a.) H2SO3

b.) HBr

c.) HSO3-

d.) Br-

14

The pH Scale - The Power of Hydrogen:

pH = direct measurement of in a solution

The pH scale is designed to measure an aqueous solution is. The concentration of hydronium and hydroxide ions in a solution will determine whether a solution is acidic or basic.

The pH scale ranges from (ACIDIC à neutral à BASIC)

In an acidic substance (brackets indicate concentration) In a basic substance In a neutral substance Example: H2O

7 14 0

ACIDIC NEUTRAL BASIC

The pH scale is based on the .

Two water molecules will sometimes combine into hydronium and hydroxide

ions.

Pure water is considered to be neutral because the hydronium ion concentration is 1.0 x 10-7 mol/L which is equal to the hydroxide ion concentration.

[H3O+]X[OH-] = (1.0 x 10-7)X(1.0 x 10-7) =

Lesson 7:

15

The pH scale is LOGARITHMIC (based on exponents of the number 10) therfore each change of a signifies

Ex: A change from a ph of 4 to a pH of 5 becomes

more/less basic; [OH-] increases/decreases by a factor of _______

more/less acidic; [H+] increases/decreases by a factor of _______

Ex: A change from a pH of 13 to a pH of 10 becomes

more/less acidic; [H+] increases/decreases by a factor of _______

more/less basic; [OH-] increases/decreases by a factor of _______

Sample Problems1. What is the pH of an HCl solution which has a [H3O+] = 1.0 x 10-3?

2. What is the hydronium[H3O+] concentration of nitric acid if the pH=4.0?

3. What is the pH of 0.010 mol/L hydrochloric acid?

4. What is the pH of an HCl solution which has a [H3O+] = 1.0 x 10-8?

5. What is the pOH of an HCl solution which has a [H3O+] = 1.0 x 10-8?

16

(Where some common substances fall on the pH scale)

STRONG acids and bases ionize 100%: http://www.chemistry.uoguelph.ca/educmat/chm19104/chemtoons/chemtoons3.htm

Strong base (sodium hydroxide): NaOH (s) Na+ (aq) + OH- (aq) (100% ionization)

Strong acid (hydrochloric acid): HCl H+ + Cl--

(100% ionization)

WEAK acids and bases have < 100% ionization (partial ionization) http://www.chemistry.uoguelph.ca/educmat/chm19104/chemtoons/chemtoons4.htm

Strong acid (acetic acid): HC2H3O2 H+ + C2H3O2Cl--

(partial ionization)

http://www.mhhe.com/physsci/chemistry/chang7/esp/folder_structure/ac/m2/s2/index.htm

Weak Base (ammonia): NH3 + H2O NH4+ + OH-

(partial ionization)

Strong Acids Strong Bases

HCl LiOH

HBr NaOH

HI KOH

H2SO4 RbOH

HNO3 CsOH

HClO4 Ba(OH)2

Sr(OH)2

Ca(OH)2

*Ammonia and the –OH in water battle for hydrogen. Roughly 1/10,000 times, ammonia wins, generating a SLIGHT excess of OH – ions, making the solution BASIC.

17

Acid-Base Indicators (Table M): http://en.wikipedia.org/wiki/Phenolphthalein

= substance (weak acid) that as a result of a pH CHANGE; indicators are chosen based on their RANGE for COLOR CHANGE

Phenolphthalein à up until a pH of 8, from 8 to 9, and at a pH greater than 9

Ex: Methyl Orange turns RED in a solution with a pH of less than 3.1, ORANGE between 3.1 and 4.4, and YELLOW in a solution with a pH greater than 4.4

*Litmus listed is liquid litmus (similar to paper litmus)** Within the “Approximate pH Range for Color Change” a MIXTURE

OR BLENDING of the two colors listed occurs. This range is therefore also called the INTERMEDIATE COLOR REGION.

1. bromthymol blue at a pH of 6.4 ____________________2. bromcresol green at a pH of 5.0 ____________________3. phenolphthalein at a pH of 8.5 ____________________4. methyl orange at a pH of 3.9 ____________________

Lesson 8:

18

Using reference table M, complete the chart below.

Indicator pH of sample Color indicator will turn

methyl orange 6.0

bromothymol blue 2.0

phenolphthalein 7.0

Litmus 6.8

bromocresol green 3.0

thymol blue 7.0

methyl orange 2.2

bromothymol blue 8.2

phenolphthalein 10

Litmus 3.2

bromocresol green 6.2

thymol blue 10

19

Neutralization Reactions: http://www.youtube.com/watch?v=8IRI5gPR5EY&safe=active

= neither acidic nor basic;

Neutralization occurs when an Arrhenius acid and an Arrhenius base react to form

Example: Antacid for upset stomach neutralizes the acid in stomach and makes a neutral salt to provide relief

General reaction for neutralization reactions:

(1) The H+ from the acid and the OH- from the base combine to form water.

(2) The ANION from the acid and the CATION from the base combine to produce a salt.

*Neutralization rxns are always reactions!**Remember, just like any compound, the (+) and (-) charges must be

balanced. Use the Criss Cross Rule to figure out the correct formula for the salt – water is always the formula H2O!

Net ionic equation for neutralization reactions (after spectator ions are crossed out):

H+(aq) + OH-(aq) H2O(l)

Lesson 9:

20

Complete the following reactions. Make sure they are balanced!

1. HBr + KOH __________ + __________

2. NaOH + HC2H3O2 __________ + __________

3. KOH + H3PO4 __________ + __________

4. 2HNO3 + Ca(OH)2 __________ + __________

21

(Acid-Base) Titration:

Titrations are used to

Acid of unkown molarity is reacted with a carefully measuredamount of a base of known molarity to the point ofNEUTRALIZATION (or vice versa)

In all neutralization reactions there must be a between the MOLES OF H+ IONS and the MOLES OF OH- IONS

So, in a titration, when: [H+] = [OH-]

or MOLES OF H+ IONS = MOLES OF OH- IONS

that means you’ve reached the EQUIVALENCE POINT of the reaction; this is when the titration is complete. The of a titration is the pH of the solution at the desired color (change).

What does a Titration look like? http://mhhe.com/physsci/chemistry/animations/chang_7e_esp/crm3s5_5.swf

Titration formula (Table T):

Where: MA = VA =

MB = VB =

Use this formula when you are dealing with atitration or neutralization word problem

Make sure that all units are in agreementwhen plugging into formula (so they cancel outand you get the right answer!)

Lesson 10:

22

Sample Problem 1: What is the concentration of a solution of HI if 0.3 L is neutralized by 0.6 L of 0.2 M solution of KOH?

Sample Problem 2: What is the concentration of a hydrochloric acid solution if 50.0 mL of a 0.250 M KOH solution are needed to neutralize 20.0 mL of the HCl solution of unknown concentration?

Sample Problem 3: A particular acid has an H+ concentration of 0.1 M and a volume of 100 mL. What volume of a base with a 0.5 M [OH-] will be required to neutralize the reaction?

**Sample Problem 4: You have 50 mL of 1.0 M H2SO4(aq). What volume of 0.5 M NaOH would be required to neutralize the acid? Remember à Diprotic Acids yield 2 H+ ions in solution!

23

Reactions of Metals with Acids:

According to in your Reference Tables, any to produce H2 gas and a salt

Example: Which metal, Mg or Cu will react with HCl?

General Rxn:

Of the four types of reactions that we have learned, this is a

reaction; notice how H2 GAS is produced!

Ex: do not react with acids because they are located

(notice these are metals used for JEWELRY!)

Lesson 11:

24

Reactions of Metals with Water:

GROUP I METALS:

GROUP II METALS: Summary of the trend for Group II Metals: the Group II Metals

become more reactive with water as you go DOWN the group

25