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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 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
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
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
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
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
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
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