Unit 9 (chapter 19) Acids and Bases

Did you know that acids and bases play a key role in much of the chemistry that affects your daily life? What effects do you think they have on each of the following pictures?

Properties of Acids 1. Taste sour. 2. Cause certain dyes (called indicators) to change colors. (Acids turn Litmus Red) 3. pH from 0.1 (strong) – 6.9 (weak) 4. Aqueous solutions are electrolytes. 5. Produce hydronium ions, H 3 O +, in water. (Often referred to as Hydrogen ions, H + ) 6. Metals react with acids to produce hydrogen gas.

The chemical formulas of acids are of the general form HX. H = hydrogen ion H = hydrogen ion X = any monatomic or polyatomic anion X = any monatomic or polyatomic anion

1.When the name of the anion (X) ends in –ide, the acid name begins with the prefix hydro-. The name ends in the suffix –ic. ex: HCl = hydrochloric acid

3. When the anion ends in –ate, the acid name ends in –ic. HNO 3 = nitric acid HNO 3 = nitric acid 2. When the name of the anion ends in –ite, the acid name ends in –ous. H 2 SO 3 = sulfurous acid

Properties of Bases 1. Taste bitter and feel slippery. 2. Cause indicators to change color. (Bases turn Litmus Blue) 3. pH from 7.1(weak) – 14(strong) 4. Aqueous solutions are electrolytes. 5. Produces hydroxide ions, OH -, in water. 6. Make good cleaners Bases react with acids to produce a salt and water.

Naming Bases The Chemical formulas for bases are of the general form of having a metal connected to a hydroxide ion(s). The name of the metal, add hydroxide to the end The name of the metal, add hydroxide to the end NaOH = Sodium Hydroxide NaOH = Sodium Hydroxide LiOH = Lithium Hydroxide LiOH = Lithium Hydroxide KOH = Potassium Hydroxide KOH = Potassium Hydroxide

In 1887, the Swedish chemist Svante Arrhenius (1859 – 1927) said that acids are hydrogen- containing compounds that ionize to yield hydrogen ions (H + ) in aqueous solution. He also said that bases are compounds that ionize to yield hydroxide ions (OH - ).

Monoprotic Monoprotic acids, contain one ionizable hydrogen, such as nitric acid (HNO 3 ). Diprotic Diprotic acids, contain two ionizable hydrogens, such as sulfuric acid (H 2 SO 4 ). Triprotic Triprotic acids, contain three ionizable hydrogens, such as phosphoric acid (H 3 PO 4 ).

Johannes Bronsted Thomas Lowry They independently defined an acid as a hydrogen- ion donor and a base as a hydrogen-ion acceptor.

A conjugate acid is the particle formed when a base gains a hydrogen ion. A conjugate base is the particle that remains when an acid has donated a hydrogen ion.

Base Acid Conjugate Conjugate Acid Base NH 3 + H 2 O NH OH - conjugate acid-base pair

Water as an Acid or a Base Water is amphoteric Water is amphoteric It can act as either an acid or a base. It can act as either an acid or a base. H 2 O + H 2 O H 3 O + + OH - Water Water Hydronium Hydroxide

Gilbert Lewis (1875 – 1946) A Lewis acid is a substance that can accept a pair of electrons to form a covalent bond. A Lewis base is a substance that can donate a pair of electrons to form a covalent bond.

K w = [H + ] x [OH - ] = 1.0 x [ ] = concentration of…

Acidic solutions = [H+] is greater than [OH-], therefore [H+] is greater than 1.0 x M, and a pH less than 7.0 Acidic solutions = [H+] is greater than [OH-], therefore [H+] is greater than 1.0 x M, and a pH less than 7.0 Neutral Solutions = [H+] is equal to [OH-], thus [H+] = 1.0 x M and a pH of 7.0 Neutral Solutions = [H+] is equal to [OH-], thus [H+] = 1.0 x M and a pH of 7.0 Basic Solutions = [H+] is less than [OH-], therefore [H+] is less than 1.0 x M, and a pH greater than 7.0. Basic Solutions = [H+] is less than [OH-], therefore [H+] is less than 1.0 x M, and a pH greater than 7.0. Basic solutions are also known as alkaline solutions Basic solutions are also known as alkaline solutions

Determines if a solution is an acid or a base. pH = the negative logarithm of the hydrogen-ion concentration. pH = -log[H + ]

Neutral Increasing AcidityIncreasing Basicity

What is the pH of a solution with [H + ] = 1 x M ? pH = 4 What is the pH of a solution with [OH - ] = 1 x M ? Since [H + ] x [OH - ] = 1 x , [H + ] = 1 x pH = 8

What is the pH of a solution if [OH - ] = 4.0 x M ? K w = [OH - ] x [H + ] = 1 x M pH = -log[H + ] = [H + ] = 1 x M = 4.0 x M 2.5 x M -log(2.5 x M) = -(log log ) pH = - (.40) – (-4) pH = 3.60

STRONG vs. WEAK Acids/Bases Strong Acids/Bases completely ionize in aqueous solution. (Ex: HCl, H 2 SO 4, NaOH) Strong Acids/Bases completely ionize in aqueous solution. (Ex: HCl, H 2 SO 4, NaOH) Weak Acids/Bases ionize only slightly in aqueous solution (Ex: H 2 CO 3, HClO, NH 3 ) Weak Acids/Bases ionize only slightly in aqueous solution (Ex: H 2 CO 3, HClO, NH 3 ) K a = Acid dissociation constant. The larger the K a value, the stronger the Acid. K a = Acid dissociation constant. The larger the K a value, the stronger the Acid. K b = Base dissociation constant. Larger K b, the stronger the base. K b = Base dissociation constant. Larger K b, the stronger the base.

The reaction of an acid with a base produces water and a salt. neutralization This is a neutralization reaction. HCl (aq) + NaOH (aq) NaCl (aq) + H 2 O (aq) Acid Base Salt Water

What acid and base could you mix to make sodium sulfate?

Strong acid + strong base Neutral solution Strong acid + weak base Acidic solution Weak acid + strong base Basic solution

An indicator changes color with pH to let a person know if a substance is an acid or a base. Examples: litmus, phenolphthalein, thymol blue, etc.

A pH meter is used to make rapid, accurate pH measurements. It consists of a reference electrode that must first be calibrated with solutions of known pH. Measurements with a pH meter are typically accurate to within 0.01 pH unit.

Solutions in which the pH remains relatively constant when small amounts of acid or base are added. A buffer is a solution of a weak acid and one of its salts, or a solution of a weak base and one of its salts.

The amount of acid or base that can be added to a buffer solution before a significant change in pH occurs.

You can make a solution less concentrated by diluting it with solvent. The number of moles of solute does not change when a solution is diluted; only the amount of solvent changes.

moles of solute before dilution = moles of solute after dilution Moles of solute = Molarity (M) x liters of solution (V) M 1 x V 1 = M 2 x V 2

The process of adding acid to base or vice versa to determine the unknown concentration of one of the solutions. The solution of known concentration is called the standard solution.

neutralization A titration is continued until the indicator shows that neutralization has just occurred. endpoint This happens when the indicator changes color and is called the endpoint in the titration. hydroxide hydrogen At the endpoint, the hydroxide and hydrogen ion concentrations are equal.

1. Add a measured volume of the standard solution (Acid or Base) 2. Add several drops of indicator to the solution. 3. Add the unknown solution drop by drop until the endpoint of the titration is reached. (be sure to record the starting and ending volume)

How many milliliters of 0.45M HCl will neutralize 25mL of 1.0M KOH? How many milliliters of 0.45M HCl will neutralize 25mL of 1.0M KOH? What is the molarity of H 3 PO 4 if 15 mL is completely neutralized by 38.5 mL of 0.150M NaOH? What is the molarity of H 3 PO 4 if 15 mL is completely neutralized by 38.5 mL of 0.150M NaOH?