Acids and Bases

Acids and Bases Some of our favorite foods make our tongue curl up because they are SOUR.

Bitter! Some foods have a “bite” of their own because they’re somewhat bitter. WHY?

Acidic/Basic There is a scientific reason for this: These foods are either acidic or basic. Other substances besides foods have these characteristics.

Acids and Bases Chemicals may be classed as acids or bases. Things that are neither acids nor bases are neutral. pH measures how acidic or basic a solution is.

Acids Often taste sour Strong acids can burn skin & eyes Strong acids can dissolve metals Examples: Lemon juice Vinegar Car battery acid (dangerous!)

Bases Can taste bitter, sweetish, or salty Strong bases can burn skin & eyes Bases react more easily with protein than with metal; they are often used for cleaning Examples: Milk Baking soda Soap Drain cleaner (dangerous!)

Some substances are not really an acid or a base: For example, pure water

The Nomenclature of ACIDS Acids are easy to recognize as compounds as they begin with the element hydrogen. As with other ionic bonds, acids fall into 2 categories, binary and ternary.

The Nomenclature of ACIDS Examples of binary acids would include things like: HF, HI, H2S and HCl Examples of ternary acids would include things like: H2SO4 and HNO3

The Nomenclature of ACIDS Naming of binary acids Step 1:Name the anion, changing the ending to “-ic” Step 2: Add the prefix “hydro-” Step 3: Slap acid on the end

“hydroflouric acid” The Nomenclature of ACIDS Example #1: HF “fluorine” becomes “fluoric” becomes “hydrofluoric” becomes “hydroflouric acid”

Naming of ternary acids The Nomenclature of ACIDS Naming of ternary acids Step 1:Name the polyatomic Step 2: Change “-ate” to “-ic” or “-ite” to “-ous” Step 3: Slap acid on the end

“sulfuric acid” The Nomenclature of ACIDS Example #1: H2SO4 “sulfate” becomes “sulfuric” becomes “sulfuric acid”

Rules for Writing Formulas for binary acids The Nomenclature of ACIDS Rules for Writing Formulas for binary acids Step 1: Does the name begin with “hydro-”? If yes, then… Step 2:Write the symbol for the hydrogen ion followed by the symbol for the second element Step 3: Crisscross the charges and write them as subscripts.

The Nomenclature of ACIDS Rules for Writing Formulas for binary acids Example: hydrosulfuric acid

The Nomenclature of ACIDS Rules for Writing Formulas for binary acids Example: hydrosulfuric acid H+1 S-2

The Nomenclature of ACIDS Rules for Writing Formulas for binary acids Example: hydrosulfuric acid H+1 S-2

H2S The Nomenclature of ACIDS Example: hydrosulfuric acid H+1 S-2 Rules for Writing Formulas for binary acids Example: hydrosulfuric acid H+1 S-2 H2S

Rules for Writing Formulas for ternary acids The Nomenclature of ACIDS Rules for Writing Formulas for ternary acids Step 1: Does the name begin with “hydro-”? If no, then… Step 2:Write the symbol for the hydrogen ion followed by the appropriate polyatomic ion Step 3: Crisscross the charges and write them as subscripts.

Rules for Writing Formulas for binary acids Example: sulfuric acid The Nomenclature of ACIDS Rules for Writing Formulas for binary acids Example: sulfuric acid

Rules for Writing Formulas for binary acids Example: sulfuric acid The Nomenclature of ACIDS Rules for Writing Formulas for binary acids Example: sulfuric acid H+1 SO4-2

Rules for Writing Formulas for binary acids Example: sulfuric acid The Nomenclature of ACIDS Rules for Writing Formulas for binary acids Example: sulfuric acid H+1 SO4-2 H+1 SO4-2

Rules for Writing Formulas for binary acids Example: sulfuric acid The Nomenclature of ACIDS Rules for Writing Formulas for binary acids Example: sulfuric acid H+1 SO4-2 H+1 SO4-2 H2SO4

The Nomenclature of ACIDS Name the chemical or write the symbol 1. HI 2. phosphoric acid 3. hydrobromic acid 4. H2SO3

The Nomenclature of ACIDS Name the chemical or write the symbol hydroiodic acid 1. 2. phosphoric acid 3. hydrobromic acid 4. H2SO3

The Nomenclature of ACIDS Name the chemical or write the symbol hydroiodic acid 1. 2. 3. hydrobromic acid 4. H2SO3 H3PO4

The Nomenclature of ACIDS Name the chemical or write the symbol hydroiodic acid 1. 2. 3. 4. H2SO3 H3PO4 HBr

The Nomenclature of ACIDS Name the chemical or write the symbol hydroiodic acid 1. 2. 3. 4. H3PO4 HBr sulfurous acid

pH Scale We use this scale to measure the strength of an acid or base. pH is defined as the –log[H+] pH can use the concentration of hydronium ions or hydrogen ions.

7 Acid Base pH Scale 14 Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 515

pH of Common Substances Timberlake, Chemistry 7th Edition, page 335

The pH Scale pH scale ranges from 0 -14 pH 7 is neutral; neither acid nor base Pure water is pH 7 Low pH (0-6.9) = acid High pH (7.1-14) = base The closer to the ends of the scale, the stronger the solution is

0--------------7---------------14 Acid Any substance which has a pH of value of less than 7 is considered an acid 0--------------7---------------14 Acid Neutral Base

0--------------7---------------14 Base Any substance which has pH value greater than 7 is a base 0--------------7---------------14 Acid Neutral Base

pH 7 A pH of 7 is called neutral—neither acid nor base. 0------------7------------14 Acid Neutral Base

The pH Scale Each pH unit is 10 times as large as the previous one A change of 2 pH units means 100 times more basic or acidic x10 x100

The pH Scale Careful measurement is important A mistake of one pH unit means 10 times too much or too little! x10 x100

How Do We Measure pH? One way to measure pH is by using special strips of paper called pH paper

How Does It Work? The paper is treated with chemicals (indicators) that change color to show the pH. When the paper touches the substance being tested, it turns a specific color to tell if the substance is an acid or a base.

To Use pH Paper Place the edge of the pH paper into the mixture. Observe the color change of the pH paper Match the resulting color to the colors listed on the outside of the pH paper package. The colors match with a correlated pH number. The number is the pH value of the sample.

Historical views on acids The Oldest Theory is the Arrhenius Theory

Arrhenius looked at the substances which were called acids Arrhenius looked at the substances which were called acids. Some of these substances were known from even before the days of alchemy. They taste sour, turn blue litmus to red, neutralize bases, release hydrogen gas when added to an active metal and release carbon dioxide when added to a carbonate. Arrhenius said these properties were due to the production of H+ ions when acids dissolve in water.

He looked at the properties of bases He looked at the properties of bases. They taste bitter, feel slippery (soapy), turn red litmus blue and neutralize acids. Arrhenius said these properties were due to the production of OH- ions when bases are dissolved in water.

Historical views on acids O2 found in oxyacids (e.g. H2SO4) was originally thought to cause acidic properties. Later, H2 was implicated, but it was still not clear why CH4 was neutral. Arrhenius made the revolutionary suggestion that some solutions contain ions & that acids produce H2+ ions in solution. + H O H O Cl Cl H + + Ionization

Historical views on acids The more recent Bronsted-Lowry concept is that acids are H+ (proton) donors and bases are proton acceptors + H O H O Cl Cl H + +

The Bronsted-Lowry concept In this idea, the ionization of an acid by water is just one example of an acid-base reaction. + Cl H O acid base conjugate acid conjugate base conjugate acid-base pairs Acids and bases are identified based on whether they donate or accept H+. “Conjugate” acids and bases are found on the products side of the equation. A conjugate base is the same as the starting acid minus H+.

The Bronsted-Lowry concept Today we know that a bare proton does not exist in water, it forms a chemical bond with a water molecule forming the H3O+. This ion is called the hydronium ion. H2O   H3O+ + OH- “Pure” water is always a dynamic mixture of these three substances in equilibrium

The Bronsted-Lowry concept 1) A B/L acid is the species which donates a proton in a proton transfer reaction. What is meant by a proton here? 2) A B/L base is the species which _________ . 3) A B/L acid is the species which _________

HCl(aq) + H2O(l)  H3O+(aq) + Cl-(aq) 4) A specific strong acid - base reaction: HCl(aq) + H2O(l)  H3O+(aq) + Cl-(aq) HCl(aq) is the ___________________ . H2O(l) is the ________________ . H3O+(aq) is the ________________________. Cl-(aq) is the _________________________ .

CH3COOH is the _____________________. H2O is the _________________________. H3O+ is the ____________________. CH3COO- is the _____________________.

Practice problems Identify the acid, base, conjugate acid, conjugate base, and conjugate acid-base pairs: HC2H3O2(aq) + H2O(l)  C2H3O2–(aq) + H3O+(aq) acid base conjugate base conjugate acid conjugate acid-base pairs OH –(aq) + HCO3–(aq)  CO32–(aq) + H2O(l) base acid conjugate base conjugate acid conjugate acid-base pairs

OYO Practice 1. HF(aq) + SO32–(aq) 2.CO32–(aq) + HC2H3O2(aq) 3. H3PO4(aq) + OCl –(aq)

Answers: OYO Practice 1. HF(aq) + SO32–(aq)  F–(aq) + HSO3–(aq) acid base conjugate base conjugate acid conjugate acid-base pairs 2. CO32–(aq) + HC2H3O2(aq)  C2H3O2–(aq) + HCO3–(aq) base acid conjugate base conjugate acid 3. conjugate acid-base pairs H3PO4(aq) + OCl –(aq)  H2PO4–(aq) + HOCl(aq) acid base conjugate base conjugate acid conjugate acid-base pairs

Reaction Types HCl + NaOH  NaCl + H2O HCl + NaOH  NaCl + H2O Neutralization Reaction – a special double replacement reaction in which an acid is combined with a base and yields water and a salt. HCl + NaOH  NaCl + H2O HCl + NaOH  NaCl + H2O

Titrations In a titration a solution of accurately known concentration is added gradually added to another solution of unknown concentration until the chemical reaction between the two solutions is complete. End point – the point at which the reaction becomes complete Equivalence point – the point at which the reaction is neutral Indicator – substance that changes color at (or near) the equivalence point Slowly add base to unknown acid UNTIL the indicator changes color 4.7

Ma x Va = Mb x Vb What volume of a 1.420 M NaOH solution is Required to titrate 25.00 mL of a 4.50 M H2SO4 solution? WRITE THE CHEMICAL EQUATION! H2SO4 + 2NaOH 2H2O + Na2SO4 Ma x Va = Mb x Vb