Acids and Bases – Unit 13

Chemistry of Acids and Bases1. Watch video and complete worksheet

2. Gallery walk to complete notes on pages 3-5 in packet

3. Homework is on page 6 in packet

Standard Deviants Teaching Systems: Chemistry: Module 05: Acids and Bases

http://app.discoveryeducation.com/player/view/assetGuid/DBD191DB-A10E-43C2-8DDE-A73858F12FE2

Unit 13 – Acids and BasesNotes #1: Intro

Acids: Something that produces a hydrogen ion (H+) in solution

Unit 13 – Acids and BasesNotes #1: Intro

• Properties of Acids:• Tart or sour taste (lemon juice)• Electrolytic• Both strong and weak• Will cause indicators to change colors• A metal + an acid will produce hydrogen

gas• Single replacement reaction

• Acid + metal → hydrogen gas + a “salt”• Double replacement reaction

• Acid + Base → water + a “salt”

• Single replacement reactionAcid + Metal → __Hydrogen gas_ + a “_salt_”

• Double replacement reactionAcid + Base → _water__ + a “_salt_”

Remembering Acid Naming Rules

“Handle acids carefully so you don’t get a case of “ate-ic-ite-ous.””

Polys ending in “-ate” are changed to “-ic”

Polys ending in “-ite” are charged to “-ous”

Hydro- prefix is not used with poly containing acids!!!!!

ION TYPE ION ENDING ACID NAME BEGINNING ACID ENDING

Polyatomic-ite NO hydro- beginning -ous

-ate NO hydro- beginning -ic

Monatomic -ide hydro- beginning -ic

Examples of Naming Binary Acids

HCl

HF

HBr

Hydrochloric acid

Hydrofluoric acid

Hydrobromic acid

Examples of Naming Ternary Acids H2SO4

H2CO3

H2NO2

Sulfate is the poly, so sulfuric acid

carbonate is the poly, so carbonic acid

Nitrite is the poly, so nitrous acid

• Base: Something that produces a hydroxide ion (OH-) in solution

Unit 13 – Acids and Bases• Properties of Bases:

• bitter• slippery (soap)• electrolytic• Both strong and weak• Will cause an indicator to

change colors

• Naming Bases • The easiest are the bases, since most of these are

_metal hydroxides, compounds you already know how to name.

• Metal hydroxides are named in the same way any other ionic compound is named. First give the name of the _metal_ ion. Follow this with the name of the anion, which, in the case of bases, is “__hydroxide__”.• KOH –• Mg(OH)2 –

Potassium HydroxideMagnesium Hydroxide

Other definitions of Acids and Bases

Arrhenius Acids and Bases:

Acid:

Hydrogen containing compound that ionize to yield a hydrogen ion in solution.

Base:

Compounds that ionize to yield a hydroxide ion in solution.

Brønsted – Lowry Acids and Bases

They felt the Arrhenius definition was too limiting.

Acids:

Hydrogen ion donor (Proton donor)

Bases:

Hydrogen ion acceptor (Proton acceptor)

Brønsted – Lowry Acids and Bases

Examples:

NH3 + H2O ↔ NH4+ + OH-

H2O donated the H+ - Acid

NH3 accepted the H+ - Base

HCl + H2O ↔ H3O + + Cl-

HCl donated the H+ - Acid

H2O accepted the H+ - Base

Amphoteric: Substance that can act as both an acid or a base.

Background Theory:

The oxides of metals are basic in nature. For example, the oxides of the alkali metals (Group I) form alkali or basic solutions.

o Sodium oxide + water → Sodium hydroxide solution

Na2O(s) + H2O(l) → NaOH(aq)

The soluble oxides of non-metals are acidic in nature. Examples include, carbon dioxide, sulfur dioxide and nitrogen dioxide.

o Sulfur dioxide + water → Sulfurous acid

SO2(g) + H2O(l) → H2SO3(aq)

o Insoluble non-metallic oxides like carbon monoxide do not form acidic solutions. This is often the cause of acid rain.

Compounds such as the amino acids, which contain both acidic and basic groups in their molecules, can also be described as amphoteric.

Strong Acids and Bases

Strong Acids/Bases:

Those that ionize completely in solution.

Ex: HCl, NaOH

Weak Acids/Bases:

Those that only slightly ionize in solution.

Ex: NH3, Acetic Acid (vinegar)

Tooth decay is caused by the weak acid – lactic acid: C3H6O3

Homework: pg 6

The pH Scalepg 7-

pH Scale

MEASURING pHScientists use a pH scale to measure the strength of an acid or base. The term pH stands for “potential for hydrogen”. The amount of hydrogen in a substance determines its acidity or alkalinity. Alkaline is another term for base. A number on the pH scale is used to describe the strength of acidity or alkalinity. The most commonly used pH scale goes from 1 (very acidic) to 14 ( very basic). The number 7 on a pH scale means neutral –neither acid nor base.

Acids play important roles in the chemistry of living things. Many of the foods you eat are acids in vitamins like ascorbic acid or vitamin C, and folic acid. Other acids help the body such as stomach acids and others are waste products of cell processes like lactic acid in working muscles. Acids also are used to make valuable products for homes, farms and industries. People often use dilute solutions of acids to clean brick and other surfaces. Hardware stores sell muriatic (hydrochloric ) acid, which is used to clean bricks and metals. Industry uses sulfuric acid in car batteries, to refine petroleum and to treat iron and steel. Farmers depend on the nitric acid and phosphoric acid to make fertilizers for crops, lawns, and gardens.

The concentration of hydrogen ions in a solutionis described by its number on the pH scale.

• A low pH tells you that the concentrationof hydrogen ion is high.

EX: pH 2• By comparison, a high pH tells you that the concentration of hydrogen ion is low.

EX: pH 12

Self-ionization of water

Self-ionization of water:Reaction in which 2 water

molecules produce ionsH2O + H2O → OH- + H3O+

Also written as: H2O ↔ H+ + OH-

The H3O+ and H+ represent hydrogen ions in solution.

Neutral Solutions

In pure water, the concentration of hydrogen ions is equal to the concentration of hydroxide ions1 x 10-7M or pH of 7

Remember M represents Molarity

[H+] = [OH-] (brackets represent concentration)

This represents a neutral solution.

Solutions In a solution, if the [H+] increases, the [OH-] decreases and

vice versa. Think back to a see-saw. As one person went up the other

went down. Ion-product constant of water, Kw:

Kw = [H+] x [OH-] = 1 x 10-14M Acidic Solution:

The [H+] will be greater than the [OH-]. Therefore, the [H+] is greater than 1 x 10-7M.

Think about the # line. -5 is GREATER than -7 Basic Solution:

The [H+] will be less than [OH-]. Therefore, the [H+] is less than 1 x 10-7M. A.k.a. alkaline solutions

NUMBER LINE and pH

Remember the number line

Which is greater? 0 or 3 3

Which is greater? -7 or -4 -4

Which is less? -2 or -4 -4

3 4 5 6 7 8210-1-2-3-4-5-6-7

Increasing

Acids Bases

Homework pg. 9

pH Calculations

The pH scale ranges from 0-14.

0 = very acidic

7 = neutral

14 = very basic

pH = -log [H+]

What is the pH of a neutral solution?

Calculate using the Logarithmic function on

the calculator (see at right)

Sample Problems

As long as you have a 1 x 10 to some power, the pH is the exponent.

1. What is the pH of the following concentrations?

a. [H+] = 1 x 10-2M

b. [H+] = 1 x 10-9M

c. [H+] = 1 x 10-5M

pH = 2 acidic

pH = 9 basicpH = 5 acidic

Sample Problems

If you do not have 1 to the power then you MUST use our formulas.

2. What is the pH of the following?

a. [H+] = 2x10-2

pH = -log(2x10-2) = 1.7 pH

b. [H+] = 6x10-9

pH = -log(6x10-9) = 8.2 pH

c. [H+] = 3x10-5

pH = -log(3x10-5) = 4.5 pH

Other Formulas and Problems

pH 14 = pH + pOH (See example 1 in Example Problems))

Equilibrium constant labeled as Kw

Kw is 1x10-14

Kw = [OH-] x [H+] = 1x10-14

Other Formulas and Problems

EX: What is the pH of a solution with a [OH-] of 4.0 x 10-11M?

o Use Kw to find [H+] then find pH using –log function.

Step1:

Step 2:

Kw = [OH-] x [H+] = 1x10-14

[H+] = 1x10-14/4x10-11 = 2.5x10-4

pH = -log [H+] pH= -log(2.5x10-4) = 3.6

1. If pH = 5, pOH =

pH 14 = pH + pOH

14 = 5 + pOH

14 – 5 = 9 pOH

Acid because pH = 5

2. What is the pH of a solution that has a hydrogen ion concentration of 1.0 x 10-5M? Is this solution acidic, basic or neutral?

Given: [H+] Solving for: pH

pH = - log [H+]

pH = - log(1.0 x 10-5 M)pH = 5pH < 7

ACIDIC

3. What is the hydrogen ion concentration of a solution with a pH of 11? Which has a greater concentration: H+ or OH-?

[H+] = 1 x 10 -11 M

more OH-, So basic

4. What is the pH of a solution that has a hydrogen ion concentration of 1.2 x 10-8M? Is this solution acidic, basic or neutral?

Given: [H+]Solving for: pH

pH = - log [H+]

pH = - log(1.2 x 10-8 M)pH = 7.92

pH > 7BASIC

5. Assuming Kw = 1x10-14, calculate the molarity of OH- in solutions at 25ºC when the H+ concentration is 0.2M

At 25ºC, Kw = [OH-] [H+] = 1x10-14

1x10-14 = [OH-] 0.2M= 1x10-14/ .2

[OH-] = 5x10-14 M

HOMEWORK: pg 12

Neutralization Notes

Acid-Base reactions will produce salt water when completely neutralized.

Salts are compounds consisting of a(n) anionfrom an acid and a(n) cation from a base.

In general, reactions in which an acid and a base react in an aqueous solution to produce a salt and water is called Neutralization Reactions.

Neutralization Reactions Neutralization occurs when an

Acid + Base ↔ water + salt

Salt: Anion from acid and the cation from the base join together to form a salt.

Where do we see this process?• Antacids• Farmers controlling the pH of soil• Formation of caves

A strong acid + a strong base = neutral solution

Examples:

HCl + NaOH ↔ H2O + NaCl

HCl + KOH ↔ H2O + KCl

Practice: Don’t forget to balance them after you write them.

• HCl + LiOH →

• HNO3 + CsOH →

• HBr + KOH →

HOH + LiCl

CsNO3 + H2O

H2O + KBr

Titrations

Titration: The process of adding a known amount of solution of known concentration to determine the concentration of the other solution.

If you don’t know the concentration of one solution, you can figure it out by performing a neutralization reaction, or titration, with a standard solution.

A standard solution is one of known concentration.

Performing Titrations

Steps in a neutralization reaction:

1. A measured volume of an acidsolution of unknown concentration is added to a flask.

2. Several drops of indicator are added to the solution.

3. Measured volumes of a base with a known concentration are mixed into the acid until it barely changes color.

Performing Titrations, cont.

End Point: The point at which the indicator changes color. Once you have reached the end point, you can

perform calculations to find the unknown solution.

Let’s show a video!

http://app.discoveryeducation.com/search?Ntt=titration##

http://www.youtube.com/watch?v=RHTxIYDJ730

Performing Titrations, cont.

Example: A 25 mL solution of H2SO4 is completely neutralized by 18 mL of 1.0 M NaOH. What is the concentration of H2SO4 solution? Step 1: Balanced equation

____H2SO4 + ____NaOH ↔ ____Na2SO4 + ____H2O

Step 2: Use formula to solve for unknown.MaVa = MbVb

na nb

na = Number of moles of your Acid (coefficient) nb = Number of moles of your Base (coefficient)M = Molarity of acid or base V = Volume of acid or base (in Liters)

2 2

MaVa = MbVbna nb

Ma ( 25 mL) = (1.0 M)( 18 mL)1 mol 2 mol

Molarity = 0.36 M

1. How many moles of HCl are needed to neutralize 6 mols of KOH?

1st ask, what is the mol ratio and then set it up as a proportion.

HCl + KOH KCl + H2O

This equation is balanced so 1 mole HCl = 1 mole KOH

So 6 mols KOH will neutralize 6 moles HCl

2. H2SO4 + 2NaOH ↔ Na2SO4 + 2H2Oa. One mole of sulfuric acid is needed to neutralize moles of NaOH.b. How many moles of NaOH are needed to neutralize 4 moles of H2SO4?

2

Given that 1 H2SO4 = 2NaOH

So if you have 4 mols H2SO4 you will need 8 moles NaOH

Homework pg 17

Also begin working on your Review on pages: 18-21