The Chemistry of Acids and Bases To play the movies and simulations included, view the presentation in Slide Show Mode.

Acid and Bases They are everywhere Acid and Bases They are everywhere.. In your food, in the air, in your house EVEN IN YOU!!!!!

Acid and Bases

Acid and Bases

Some Properties of Acids Produce H+ (as H3O+) ions in water (the hydronium ion is a hydrogen ion attached to a water molecule) Taste sour Corrode metals Form Electrolytes (conduct electricity) when dissolved in water React with bases to form a salt and water pH is less than 7 Turns blue litmus paper to red “Blue to Red A-CID” Feel sticky

Some Properties of Bases Produce OH- ions in water Taste bitter, chalky Are electrolytes in water Feel soapy, slippery React with acids to form salts and water pH greater than 7 Turns red litmus paper to blue “Basic Blue”

Some Common Acids and Bases HCl hydrochloric acid stomach acid HC2H3O2 acetic acid vinegar H3C6H5O7 citric acid citrus fruits KOH potassium hydroxide liquid soap Mg(OH)2 magnesium hydroxide Milk of magnesia Al(OH)3 aluminum hydroxide antacid

Acid/Base definitions Definition #1: Arrhenius (original) Acids – produce H+ ions (or hydronium ions H3O+) Bases – produce OH- ions (problem: some bases don’t have hydroxide ions!)

HCl + H2O  H3O+ + Cl– – + Acids form hydronium ions (H3O+) acid Arrhenius - In aqueous solution… Acids form hydronium ions (H3O+) HCl + H2O  H3O+ + Cl– H Cl O – + acid

NH3 + H2O  NH4+ + OH- – + Bases form hydroxide ions (OH-) base Arrhenius - In aqueous solution… Bases form hydroxide ions (OH-) NH3 + H2O  NH4+ + OH- H N O – + base

Acid/Base Definitions Definition #2: Brønsted – Lowry Acids – proton donor Bases – proton acceptor A “proton” is really just a hydrogen atom that has lost its electron!

A Brønsted-Lowry acid is a proton donor A Brønsted-Lowry base is a proton acceptor conjugate acid conjugate base base acid Conjugate What??!! We’ll go over this later, but think about what it might mean…..

Summary of Definitions Arrhenius acid: Produce H+ ion Arrhenius base: Produce OH- ion Bronsted-Lowery Acid: Proton donor ** Bronsted Lowery Base: Proton acceptor **More Broad definition than Arrhenius**

How do you Identify an Acid or a Base? The chemical formula of an acid usually begins with an H HCl (hydrochloric acid) HNO3 (nitric acid) HC2H3O2 (acetic acid) The chemical formula of a base usually includes an –OH group NaOH (sodium hydroxide) Mg(OH)2 (magnesium hydroxide) NOT TRUE for the common base, ammonia NH3

Acid Nomenclature Flowchart

Acid Nomenclature Review Binary: No Oxygen Ternary: w/Oxygen He –ate –ic and got stomach –ite -ous

Acid Nomenclature Review HBr (aq) H2CO3 H2SO3  hydrobromic acid  carbonic acid  sulfurous acid

Name ‘Em! HI (aq) HCl (aq) H2SO3 HNO3 HIO4

Naming and Writing Formulas for Bases Bases are usually IONIC: metal + hydroxide Remember: NO PREFIXES WITH IONICS Example: NaOH Sodium hydroxide Mg(OH)2 - Magnesium hydroxide Most common non-hydroxide Base: Ammonia, NH3

Conjugate Acid/Base Pairs A conjugate base is what is left over after an acid donates a proton. A conjugate acid is what is formed when a base accepts a proton. HCl + H2O  Cl– + H3O+ acid base conjugate conjugate base acid

Conjugate Acid/Base Pairs HA + B- A- + BH -H+ +H+ acid = proton donor base = proton acceptor

Conjugate Acid/Base Pairs 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

You Try (a) HF(aq) + SO32–(aq)  F–(aq) + HSO3–(aq) (b) CO32–(aq) + HC2H3O2(aq)  C2H3O2–(aq) + HCO3–(aq) (c) H3PO4(aq) + OCl –(aq)  H2PO4–(aq) + HOCl(aq)

Strength of an Acid or Base Strong Acids/Bases 100% ionized in water strong electrolyte Remember: any solution that contains ions is an electrolyte: conducts Electricity - + Strong Acids HCl HNO3 H2SO4 HBr HI HClO4 Strong Bases NaOH KOH Ca(OH)2 Ba(OH)2

Weak Acids/Bases do not ionize (dissociate) completely; only a small percentage of the original acid or base molecules will dissociate. The majority stay intact (do NOT ionize) and therefore don’t make many ions. Weak acids and bases are also weak electrolytes, meaning they only conduct electricity a little. Weak Acids HF CH3COOH H3PO4 H2CO3 HCN Weak Base NH3

Acid Strength is described using the Acid Dissociation Constant Ka Acid dissociation constant, Ka= concentration of products concentration of reactants The more ionization occurs, the larger Ka, and the stronger the acid! HA + H2O H3O+ + A- Ka = [H3O+] [A-] [HA]

Acid Equilibrium Constants are greater than 1(›1) for strong acids and less than 1 (‹1) for weak acids

Equilibrium Constants for Weak Bases Kb = concentration of products concentration of reactants Weak base has Kb < 1

Ionization Constants for Acids/Bases Conjugate Bases Increase strength Increase strength

Strength of Acids and Bases The terms weak and strong are used to describe the ability of an acid or base to ionize (produce H+ or OH- ions). A strong acid ionizes completely; a weak acid only partially ionizes. Dilute and concentrated are terms used to describe how much of an acid or base (concentration) is present in a solution.

from a high concentration of a weak acid. Acids and Bases Strength Is NOT Concentration pH of a solution tells us the concentration of H+ ions in solution. A high concentration of H+ ions can result from a strong acid OR from a high concentration of a weak acid. So… you really need Ka to know how strong an acid is.

The pH scale is a way of expressing the strength of an acidic or basic solution. Under 7 = acidic 7 = neutral Over 7 = basic

pH of Common Substances

[ ] means Concentration (Molarity) Calculating pH pH = - log [H+] [ ] means Concentration (Molarity) Example: If [H+] = 1 X 10-10 M pH = - log (1 X 10-10) pH = - (- 10) pH = 10 Example: If [H+] = 1.8 X 10-5 M pH = - log (1.8 X 10-5) pH = - (- 4.74) pH = 4.74

Try These! Find the pH of these: 1) A 0.15 M solution of Hydrochloric acid 2) A 3.00 X 10-7 M solution of Nitric acid

pH calculations – Solving for H+ If the pH of Coke is 3.12, [H+] = ??? Because pH = - log [H+] then - pH = log [H+] Take antilog (10x) of both sides and get 10-pH = [H+] [H+] = 10-3.12 = 7.6 x 10-4 M *** to find antilog on your calculator, look for “Shift” or “2nd function” and then the log button or the 10x button, where x is -pH

pH calculations – Solving for H+ A solution has a pH of 8.5. What is the Molarity of hydrogen ions in the solution? pH = - log [H+] 8.5 = - log [H+] -8.5 = log [H+] Antilog -8.5 = antilog (log [H+]) 10-8.5 = [H+] 3.16 X 10-9 = [H+]

pH testing There are several ways to test pH Blue litmus paper (red = acid) Red litmus paper (blue = basic) pH paper (multi-colored) pH meter (7 is neutral, <7 acid, >7 base) Universal indicator (multi-colored) Indicators like phenolphthalein: basic is pink (backwards!) and acidic is clear.

pOH Since acids and bases are opposites, pH and pOH are opposites! pOH looks at the perspective of a base pOH = - log [OH-] If you know either pH or pOH, you can find the other easily! pH + pOH = 14

Relationship between pH, pOH, [H+] and [OH-]

[H3O+], [OH-] and pH What is the pH of a 0.0010 M NaOH solution? Be careful! NaOH is a base and produces OH- ions. [OH-] = 0.0010 (or 1.0 X 10-3 M) pOH = - log 0.0010 pOH = 3 pH = 14 – 3 = 11

The pH of rainwater collected in a certain region of the northeastern United States on a particular day was 4.82. What is the H+ ion concentration of the rainwater? The OH- ion concentration of a blood sample is 2.5 x 10-7 M. What is the pH of the blood?

Paper testing Paper tests like litmus paper and pH paper Put a stirring rod into the solution and stir. Take the stirring rod out, and place a drop of the solution from the end of the stirring rod onto a piece of the paper Read and record the color change. Note what the color indicates. You should only use a small portion of the paper.

pH meter Tests the voltage of the electrolyte (ionic solution) Converts the voltage to pH Very cheap, accurate Must be calibrated with a buffer solution

pH indicators Indicators are dyes that can be added that will change color in the presence of an acid or base. Some indicators only work in a specific range of pH Phenolphthalein is the most common indicator

Acids and Bases

Relation of Ka, Kb, [H3O+] and pH

ACID-BASE REACTIONS; a type of Double-Replacement Reaction Acid + Base → Water and salt HCl + NaOH → H2O + NaCl Acid-Base reactions are called neutralization reactions because the products are water and a salt (ionic compound).

You Try… Write balanced chemical equations for these neutralization reactions. Under each compound give the correct formula or IUPAC name. iron(II) hydroxide + phosphoric acid Ba(OH)2(aq) + HCl(aq) calcium hydroxide + nitric acid Al(OH)3(aq) + H2SO4(aq) ammonium hydroxide + hydrosulfuric acid KOH(aq) + HClO2(aq)