SOLUTIONS & ACID-BASE CHEMISTRY

Unit 11

TOPICS OVERVIEW

01

02

03

04

05

INTRODUCTION TO ACID-BASE CHEMISTRY

SOLUTIONS

ACID-BASE CALCULATIONS

NEUTRALIZATION REACTIONS & TITRATIONS

DILUTIONS & MOLARITY

SOLUTIONS

01

Solutions

A solution is a homogeneous mixture of one or more solutes dissolved in a solvent

The substance that does the dissolving is called the solvent

• The solvent is usually present in the larger quantity
• Water is considered a universal solvent because more substances dissolve in water than any other chemical

Solutions

In a solution, the substance that gets dissolved is called the solute

• The solute is present in the smallest quantity

Solute + Solvent = Solution

Dissolution vs Reaction

Dissolution (or dissolving) is a PHYSICAL change for most covalent molecules (rarely for ionic compounds)

• The substance that is dissolved simply separates into individual particles or ions within the solvent, without changing its chemical identity
• Dissolving can sometimes involve a chemical reaction
• Whether dissolving is a physical or chemical change is widely debated amongst chemistry nerds

Solubility

Solubility is the ability of one substance to dissolve in another substance at a given temperature and pressure

“Like dissolves like”

Polar substances tend to dissolve in polar solvents

Nonpolar substances tend to dissolve in nonpolar solvents

Electrolytes

If there are ions present in solution, that solution will conduct electricity

• Solutions that conduct electricity are called electrolytes
• Any soluble, ionic compound is an electrolyte

Saturation

1. A saturated solution is a solution that contains the maximum amount of solutes

Saturation

• An unsaturated solution is a solution in which more solutes can dissolve

Saturation

• A supersaturated solution is a solution that contains more solutes than is normally allowed

Supersaturation can be achieved by heating the solution then cooling it slowly

​

Supersaturated solutions are unstable

Concentration of a Solution

The amount of solute in a solution is given by its concentration and expressed using molarity

Molarity =

Calculating Molarity

What is the molarity of a solution of hydrochloric acid containing 54.7 g of hydrogen chloride in 250 mL of water?

1.50 mol

1 L = 1000 mL

250 mL =

54.7 g HCl

1 mol HCl

36.5 g HCl

= 1.4986 =

1.50 mol HCl

M =

6.0 M

0.25 L

=

0.25 L

Introduction to Acid-Base Chemistry

02

Properties, Nomenclature, Chemical Formulas

Acids

An acid is a compound that produces hydrogen ions (H⁺) in solution

• This is the Arrhenius acid definition
• Often results when hydrogen is covalently bonded to an electronegative element and the hydrogen is easily dissociated from the rest of the molecule
• Not all compounds that contain hydrogen are acids
• Only a hydrogen that is bonded to a very electronegative element can be released as an ion

Acids in Aqueous Solutions

In an aqueous solution, hydrogen ions are not technically present

• Instead the hydrogen ions are joined to water molecules
• This forms the hydronium ion H₃O¹⁺
• Chemists will often still refer to these ions as H⁺ ions

The diagram depicts hydrogen chloride (HCl) ionizing in water to form hydronium ions (H₃O¹⁺) and chloride ions (Cl^1-)

• Tastes sour
• Conduct electricity
• Corrosive (break down certain substances)
• Some acids react strongly with metals
• Turns blue litmus paper red

Properties of Acids

Bases

A base is a compound that ionizes in aqueous solution to produce hydroxide ions (OH^1-)

• Bases include the oxides, hydroxides and carbonates of metals
• The soluble bases are called alkalis

• Taste bitter
• Feel slippery
• Corrosive
• Can conduct electricity
• Do not react with metals
• Turns red litmus paper blue

Properties of Bases

Acid Nomenclature

We’re going to focus on two categories of acids:

• Binary acids: acids that have hydrogen combined with only one other nonmetallic element
• Ternary acids: acids with hydrogen, oxygen, and at least one other element (ternary = 3)

Acid Nomenclature: Guidelines

Acids are named by first identifying the ANION present

Three guidelines for naming acids:

-ide

Hydro- ____ -ic acid

-ate

____-ic acid

-ite

____-ous acid

An anion is a negatively charged ion

Binary Acids

Nomenclature:

HBr → _________________

​

HI → _________________

hydrobromic acid

hydroiodic acid

bromide →

iodide →

bromic

iodic

anion =

anion =

Binary Acids

Chemical Formulas:

1. Hydrogen is written first in the formula
2. Drop the “hydro-” prefix and “acid” from the binary acid name
3. Change the “-ic” ending back to “-ide” to determine the charge on the anion
4. Determine hydrogen’s charge
5. Criss cross the charges to write the subscripts of the chemical formula

Binary Acids

Hydrochloric acid → _______

​

​

Hydrofluoric acid → _______

hydrochloric acid

↳ chloric =

chloride

H

Cl

1+

1-

HCl

HF

hydrofluoric acid

↳ fluoric =

fluoride

H

F

1+

1-

Chemical Formulas:

Ternary Acids

Nomenclature:

H₃PO₄ → _________________

​

H₂SO₃ → _________________

phosphoric acid

sulfurous acid

PO₄^3- =

phosphate → change -ate to -ic

SO₃^2- =

sulfite → change -ite to -ous

Ternary Acids

Chemical Formulas:

• Hydrogen is written first in the formula
• Identify the polyatomic ion
• Change -ic endings back to -ate
• Change -ous endings back to -ite
• Determine the charge of the polyatomic ion
• Determine hydrogen’s charge
• Criss cross the charges to write the subscripts of the chemical formula

Ternary Acids

Carbonic acid → __________

​

​

Chlorous acid → __________

carbonic

↳ -ic → -ate =

carbonate

H

CO₃

1+

2-

H₂CO₃

HClO₂

chlorous

↳ -ous → -ite =

chlorite

H

ClO₂

1+

1-

Chemical Formulas:

Bases

Nomenclature:

We’re only going to focus on strong bases since they fully dissociate into ions in solution

• Name the cation
• add “hydroxide”

NaOH → ______________________

sodium

hydroxide

Bases

Chemical Formulas:

• Write the element symbol of the cation
• Write the element symbol for hydroxide
• Determine the charges of the cation and anion
• Criss cross the charges to write the subscripts of the chemical formula

Hint: if the charge of the cation is greater than 1, you will need to write parenthesis around hydroxide’s chemical formula when you write the subscripts

Bases

Chemical Formulas:

​

calcium hydroxide → __________

Ca

OH

2+

1-

Ca(OH)₂

Strategies for Acid-Base Nomenclature & Chemical Formulas

First, determine if you’re working with an acid or a base

If you’re given a chemical formula:

• The chemical formulas for acids will begin with H
• The chemical formulas for bases will end with OH

If you’re given the acid or base name:

• Acids will have the word “acid” in the name
• Bases will have the word “hydroxide” in the name

Writing Chemical Formulas for Acids:

If you’re working with an acid: is it BINDARY or TERNARY?

Binary = H and 1 other non-metallic element (2 elements in total)

Ternary = H and 2 other non-metallic elements (3 or more elements in total)

Writing chemical formulas:

• Binary: determine the charges on H and the anion then criss cross the charges

Example: hydrochloric acid = HCl

• Ternary: identify which polyatomic ion is the anion
• the “-ic” ending was originally “-ate”
• the “-ous” ending was originally “-ite”
• Assign the charges on H and the polyatomic ion, then criss cross them

Example: sulfuric acid = H₂SO₄

Acid Nomenclature:

If you’re working with an acid: is it BINARY or TERNARY?

Binary = H and 1 other non-metallic element (2 elements in total)

Ternary = H and 2 other non-metallic elements (3 or more elements in total)

Acid Nomenclature:

• Binary: name using the [“hydro-” prefix followed by the anion name with an “-ic” ending] + acid

Example: HBr = hydrobromic acid

• Ternary: NO PREFIX!
• Determine the polyatomic ion
• [Change the ending of the polyatomic ion] + acid
• “-ate” → “-ic”
• “-ite” → “-ous”)

Example: H₃PO₄ = phosphoric acid H₂PO₄ = phosphorous acid

Bases:

Writing chemical formulas:

• Write the element symbol for the cation
• Write the chemical formula of the anion (hydroxide)
• Criss cross the charges to write the subscripts for the chemical formula
• If the charge on the cation is greater than 1, don’t forget to put parentheses around the OH before writing the subscript

Example: strontium hydroxide = Sr(OH)₂

Base Nomenclature:

• Name the cation by its element name
• Name the OH (hydroxide)

Example: LiOH = lithium hydroxide

ACID-BASE CALCULATIONS

03

Review: Acids & Bases

Bases produce ______________ ions in solution

Acids produce ____________ ions in solution

• Solutions with a higher concentration of hydrogen ions [H⁺] will be more acidic, and vice versa

hydrogen

hydroxide

• Solutions with a higher concentration of hydroxide ions [OH^—] will be more basic, and vice versa

Neutral Solutions

The reaction in which water molecules produce ions is called self-ionization

H₂O

water molecule

H₂O

water molecule

H₃O⁺

hydronium ion

OH^—

hydroxide ion

+

+

chemists also refer to this as a:

H⁺

hydrogen ion

Self-Ionization of Water

The self-ionization of water occurs to a very small extent

In pure water at 25^oC, the concentration of hydrogen ions and the concentration of hydroxide ions is equal:

• [H⁺] = 1×10^-7 M
• [OH^—] = 1×10^-7 M

In solution, if [H⁺] = [OH^—] the solution is neutral (neither acidic or basic)

[ ] is read as “the concentration of…”

Equation 1: The Ionization Constant for Water - K_W

For aqueous solutions, the product of hydrogen ion concentration and hydroxide ion concentration equals 1.00×10^-14:

K_W = [H⁺] × [OH^—] = 1.00×10^-14

Example 1: If [H⁺] = 1.20×10^—3 M what is the [OH^—] of this solution?

[ 1.20×10^—3 ] × [OH^—] = 1.00×10^—14

( 1.20×10^—3 )

( 1.00×10^—14 )

= 8.33×10^—12 M

[OH^—] =

Acidic Solutions

A solution in which the [H⁺] that is greater than the [OH^—] is considered an acidic solution

​

acidic solutions = [H⁺] > 1.00×10^-7 M

​

Example:

hydrogen chloride in water produces hydrochloric acid:

HCl_(aq) → H⁺_(aq) + Cl^—_(aq)

Basic Solutions

A solution in which the [OH^—] that is greater than the [H⁺] is considered a basic solution

​

basic solutions = [OH^—] > 1.00×10^-7 M

​

Example:

sodium hydroxide dissolved in water produces a basic solution:

NaOH_(aq) → Na⁺_(aq) + OH^—_(aq)

The pH Scale

Expressing hydrogen ion concentration in molarity is not practical

The pH scale also expresses [H⁺] and is more widely used

The pH Scale:

Acidic solutions → pH < 7

Basic solutions → pH > 7

Neutral solutions → pH = 7

Equation 2: Calculating pH

The pH of a solution is the negative logarithm of the hydrogen ion concentration:

​

pH = —log [H⁺]

​

Example 2: If [H⁺] = 1.80×10^—5 M what is the pH of the solution?

pH = —log [ 1.80×10^—5 ]

pH = 4.74

acidic or basic?

Equation 3: Calculating [H⁺] from pH

The [H⁺] in a solution is the inverse logarithm of the negative pH:

[H⁺] = 10^-pH

Example 3: If the pH of a solution is 3.12, what is the concentration of hydrogen ions for this solution?

[H⁺] = 10^—3.12

[H⁺] = 7.59×10^-4 M

acidic or basic?

The pOH Scale

The pOH scale is similar to the pH scale, however, it expresses [OH^—]

The pOH scale is the INVERSE of the pH scale

The pOH Scale:

Acidic solutions → pOH > 7

Basic solutions → pOH < 7

Neutral solutions → pOH = 7

Equation 4: Calculating pOH

The pOH of a solution is the negative logarithm of the hydroxide ion concentration:

​

pOH = —log [OH^—]

​

Example 4: If [OH^—] = 4.82×10^—5 M, what is the pOH of the solution?

pOH = —log [ 4.82×10^—5 ]

pOH = 4.32

acidic or basic?

Equation 5: Calculating [OH^—] from pOH

The [OH^—] in a solution is the inverse logarithm of the negative pOH:

[OH^—] = 10^-pOH

Example 5: If the pOH of a solution is 5.70 what is the concentration of hydroxide ions for this solution?

[OH^—] = 10^—5.70

[OH^—] = 2.00×10^-6 M

acidic or basic?

Equation 6: Relating pH and pOH

Because K_W = [H⁺] × [OH^—] = 1.00×10^—14 :

If we take the —log of each side of that equation, use some logarithmic properties along with some substitution we get:

pH + pOH = 14

Example 4.5: If [OH^—] = 4.82×10^—5 M what is the pOH of the solution?

pOH = —log [ 4.82×10^—5 ]

pOH = 4.32

acidic or basic?

What is the pH of this solution?

pH + 4.32 = 14

pH = 9.68

Acid-Base Calculations Equations

[H⁺] × [OH^—] = 1.00×10^—14

pH = —log[H⁺] [H⁺] = 10^—pH

pOH = —log[OH^—] [OH^—] = 10^—pOH

pH + pOH = 14

No units for pH or pOH Units for [conc.] = M

answers written in scientific notation

Dilutions & Molarity

04

Dilutions

Dilution is the process used to make a new solution that is less concentrated than the original solution by adding more solvent

M₁V₁ = M₂V₂

M₁ = Initial molarity M₂ = Final molarity

V₁ = Initial volume V₂ = Final volume

Example 1:

A scientist obtains 0.250 L of concentrated 5.00 M NaCl solution. The scientist then dilutes the solution by adding water until the solution has a volume of 1.00 L. What is the final molarity of the solution?

Example 1:

M₁ =

V₁ =

M₂ =

V₂ =

5.00 M

0.250 L

?

1.00 L

M₁V₁ = M₂V₂

( 5.00 M ) ( 0.250 L ) = ( M₂) ( 1.00 L )

1.25 = 1.00 M₂

M₂ = 1.25 M

M₂ =

V₂ =

M₁ =

V₁ =

Example 2:

In a laboratory, a scientist takes 50.0 mL of a 5.00 M NaOH solution and dilutes it until the solution has a molarity of 2.00 M. What is the final volume of this dilute solution?

5.00 M

50.0 mL =

2.00 M

?

M₁V₁ = M₂V₂

( 5.00 M ) ( 0.0500 L ) = ( 2.00 M ) ( V₂ )

0.250 = 2.00 V₂

V₂ = 0.125 L

0.0500 L

Neutralization Reactions & Titrations

05

Neutralization Reactions

A neutralization reaction occurs when the reaction of a strong acid with a strong base produces a neutral solution with a pH of 7

In general, strong acids and strong bases react to produce a salt and water

• In chemistry, a salt is any ionic compound formed from an acid/base reaction

Neutralization Reactions

Acid + Base → Water + Salt

HCl + NaOH → H₂O + NaCl

HNO₃ + NaOH → H₂O + NaNO₃

Strong Acids & Strong Bases

Strong Acids:

• HBr hydrobromic acid
• HCl hydrochloric acid
• HI hydroiodic acid
• HClO₃ chloric acid
• HNO₃ nitric acid
• HClO₄ perchloric acid
• H₂SO₄ sulfuric acid

Strong Bases:

• LiOH lithium hydroxide
• NaOH sodium hydroxide
• KOH potassium hydroxide
• RbOH rubidium hydroxide
• CsOH cesium hydroxide
• Ca(OH)₂ calcium hydroxide
• Sr(OH)₂ strontium hydroxide
• Ba(OH)₂ barium hydroxide

Titrations

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

Performing a Titration

1. A measured volume of an acid (or base) of unknown concentration is added to an Erlenmeyer flask
2. Several drops of indicator are added to the solution while the flask is gently swirled
3. Measured volumes of a base (or acid) of known concentration is dispensed into the Erlenmeyer flask, usually using a buret, until the indicator just barely changes color

Performing a Titration

pH Indicators

A pH indicator is a compound that changes color in solution over a narrow range of pH values

The pH indicator selected for the titration must change color at or near the pH of the equivalence point

• The point at which the indicator changes color is called the end point

Choosing a pH Indicator

The equivalence point occurs when the acid and base have neutralized

• Neutralization occurs when the number of moles of hydrogen ions is equal to the number of moles of hydroxide ions

Titration Curves

A titration curve is a graphical representation of the pH of a solution during a titration

• If the titration is between a strong acid and strong base, the equivalence point is at a pH of 7

Determining the Unknown Concentration through Titration Calculations

X_B = moles of base (from equation)

M_A = molarity of acid

V_A = volume of acid (in L)

X_A = moles of acid (from equation)

M_B = molarity of base

V_B = volume of base (in L)

X_B M_A V_A = X_A M_B V_B

1. Start with a balanced chemical reaction equation
2. Determine the given information from the word problem
3. Plug in the values to the above equation and solve

Example 1: Reactions with 1:1 Mole Ratios

What is the concentration of HCl if 0.0300 L of 0.100 M NaOH neutralizes 0.0500 L of HCl?

____ HCl + ____ NaOH → ____ NaCl + ____ H₂O

M_A = ____________

V_A = ____________

X_A = ____________

M_B = ____________

V_B = ____________

X_B = ____________

?

0.0500 L

0.100 M

0.0300 L

1

1

Example 1: Reactions with 1:1 Mole Ratios

X_B M_A V_A = X_A M_B V_B

( 1 ) ( M_A )( 0.0500 L ) = ( 1 ) ( 0.100 M ) ( 0.0300 L )

0.0500 M_A = 0.00300

M_A = 0.0600 M HCl

____ HCl + ____ NaOH → ____ NaCl + ____ H₂O

M_A = ?

V_A = 0.0500 L

X_A = 1

M_B = 0.100 M

V_B = 0.0300 L

X_B = 1

Example 2: Reactions without 1:1 Mole Ratios

If 0.020 L of Sr(OH)₂ is neutralized after 0.025 L of 0.0500 M HCl is added, what is the concentration of the Sr(OH)₂?

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

M_A = ____________

V_A = ____________

X_A = ____________

M_B = ____________

V_B = ____________

X_B = ____________

0.0500 M

0.025 L

?

0.020 L

2

2

2

1

Example 2: Reactions without 1:1 Mole Ratios

X_B M_A V_A = X_A M_B V_B

( 1 ) ( 0.050 M ) ( 0.025 L ) = ( 2 ) ( M_B ) ( 0.020 L )

0.00125 = 0.040 M_B

M_B = 0.031 M Sr(OH)₂

2 HCl + Sr(OH)₂ → SrCl₂ + 2 H₂O

M_A = 0.050 M

V_A = 0.025 L

X_A = 2

M_B = ?

V_B = 0.020 L

X_B = 1