Acids and Bases

Properties of Acids Acids taste sour Acids effect indicators Blue litmus turns red Methyl orange turns red Acids have a pH lower than 7 Acids are proton (hydrogen ion, H+) donors Acids react with active metals, produce H2 Ex: Reactions lab Acids react with carbonates to produce CO2 Acids neutralize bases

Blue litmus paper turns red in contact with an acid. Acids Effect Indicators Acid Base Blue litmus paper turns red in contact with an acid.

Acids Neutralize Bases

Effects of Acid Rain on Marble (calcium carbonate) George Washington: BEFORE George Washington: AFTER

Acids React with Active Metals Magnesium Acids react with active metals to form salts and hydrogen gas. Mg + 2HCl  MgCl2 + H2(g)

Acids Taste Sour.

Dilutions of Acids ALWAYS ADD ACID TO WATER This reduces the chance that it will blow up in your face due to the heat of reaction making steam rapidly. The denser acid will sink and disperse more evenly.

An acid that contains hydrogen and one other element. Binary Acids An acid that contains hydrogen and one other element.

Naming Binary Acids The proper method to use when naming binary acids is to begin with the hydro- prefix, use the root of the nonmetal, and add the –ic suffix.

Oxyacids An oxyacid is a compound of hydrogen, oxygen, and a third element, usually a nonmetal.

Method for Naming Oxyacids If the acid consists of one more oxygen than the polyatomic ion with the -ate suffix, use the per- prefix, the root of the polyatomic ion and the –ic suffix. Example HClO4 = perchloric acid If the acid consists of a polyatomic ion with the -ate suffix, use the root of the polyatomic ion and add –ic. Example HClO3 = chloric acid If the acid consists of hydrogen and a polyatomic ion with the -ite suffix, use the root of the polyatomic ion and add –ous. Example HClO2 = chlorous acid If an acid consists of one less oxygen than the polyatomic ion ending in –ite, use the hypo prefix, the root of the polyatomic ion and the –ous suffix. Example HClO = hypochlorouc acid

Naming Acids Anion Acid _________ ide (chloride, Cl1-) Hydro____ ic acid (hydrochloric acid, HCl) add H+ ions _________ic acid (chloric acid, HClO3) (perchloric acid, HClO4) _________ ate (chlorate, ClO3-) (perchlorate, ClO4-) add H+ ions _________ite (chlorite, ClO2-) (hypochlorite, ClO-) ______ous acid (chlorous acid, HClO2) (hypochlorous acid, HClO) add H+ ions

Name the Acid

Acids you must know: Strong Acids Sulfuric acid, H2SO4 Hydrochloric acid, HCl Nitric acid, HNO3 Weak Acids Phosphoric acid, H3PO4 Acetic acid, CH3COOH

Sulfuric Acid Highest volume production of any chemical in the U.S. Used in the production of paper Used in production of fertilizers Used in petroleum refining

Nitric Acid Used in the production of fertilizers Used in the production of explosives Nitric acid is a volatile acid – its reactive components evaporate easily Stains proteins (including skin!)

Hydrochloric Acid Used in the pickling of steel Used to purify magnesium from sea water Part of gastric juice, it aids in the digestion of protein Sold commercially as “Muriatic acid”

Useful for cleaning concrete Muriatic Acid (HCl) Sold commercially Useful for cleaning concrete Buyer beware

Phosphoric Acid A flavoring agent in sodas Used in the manufacture of detergents Used in the manufacture of fertilizers Not a common laboratory reagent

Acetic Acid Used in the manufacture of plastics Used in making pharmaceuticals Acetic acid is the acid present in vinegar

Strength of Acids Acids are proton (hydrogen ion, H+) donors Strong acids are assumed to be 100% ionized in solution (good proton donors). Weak acids are usually less than 5% ionized in solution (poor proton donors).

Acids are Proton Donors Monoprotic acids Diprotic acids Triprotic acids HCl HC2H3O2 HNO3 H2SO4 H2CO3 H3PO4

Comparison of a Monoprotic Acid to a Diprotic Acid

Strong acids such as HCl ionize almost completrly in solution, forming hydronium ions, H3O+ H2O + HCl  H3O+ + Cl- Proton acceptor Proton donor

Weak acids favor reverse reactions and enter chemical equilibrium before many hydronium ions, H3O+ form.

Organic Acids Organic acids all contain the “carboxyl” group, sometimes several of them. The carboxyl group is a poor proton donor, so ALL organic acids are weak acids.

Examples of Organic Acids Citric acid in citrus fruit Malic acid in sour apples Deoxyribonucleic acid, DNA Amino acids, the building blocks of protein Lactic acid in sour milk and sore muscles Butyric acid in rancid butter

The pH scale is used to measure the strength of an acid or base The pH scale is used to measure the strength of an acid or base. A pH of less than 7 indicates an acid. The lower the pH, the stronger the acid.

pH of Many Common Substances

Properties of Bases Bases taste bitter Bases effect indicators Red litmus turns blue Phenolphthalein turns purple Bases have a pH greater than 7 Bases are proton (hydrogen ion,H+) acceptors Solutions of bases feel slippery Bases neutralize acids

Bases Effect Indicators Red litmus paper turns blue in contact with a base. Phenolphthalein turns purple in a base.

Bases Have a pH of greater than 7 Bases Have a pH of greater than 7. The greater the pH, the stronger the base.

Bases Feel Slippery and Taste Bitter

Bases Neutralize Acids Milk of Magnesia contains magnesium hydroxide, Mg(OH)2, which neutralizes stomach acid, HCl. 2 HCl + Mg(OH)2 MgCl2 + 2 H2O

Examples of Bases Sodium hydroxide (lye, Drano), NaOH Potassium hydroxide, (Caustic Potash) KOH Magnesium hydroxide, (milk of magnesia) Mg(OH)2 Calcium hydroxide (lime), Ca(OH)2

Different Acid-Base Definitions

Svante Arrhenius first defined acids to be proton (H+) donors and bases to be hydroxide ion (OH-) donors in aqueous solution.

The Arrhenius model of acids and bases is summarized by the following two reactions:

Bronsted-Lowry Definition of an Acid and Base Bronsted-Lowry Acid- a molecule or ion that is a proton donor. Bronsted-Lowry Base- a molecule or ion that is a proton acceptor.

Conjugate Acid-Base Pairs The conjugate base of a Bronsted acid is the species that remains after an acid has donated a proton. The conjugate acid of a Bronsted base is the species that is formed after the base has accepted the proton.

Bronsted Conjugate Acid-Base Pairs

The conjugate of a strong acid is a weak base The conjugate of a strong acid is a weak base. The conjugate of a strong base is a weak acid.

Example of a Weak Acid Hydrofluoric Acid, HF (Hydrogen atom- Red) (Fluorine atom- Blue)

Lewis Acids and Bases Lewis Acid- a molecule or ion that is an electron pair acceptor. Lewis Base- a molecule or ion that is an electron pair donor.

Examples of How Bases Form Bronsted Base = Proton Acceptor Lewis Base = Electron Pair Donor

Bases Neutralize Acids Evergreen shrub + concrete  dead bush Orange juice + milk  bad taste Under a pine tree + fertilizer  white powder Acid + Base  Salt + Water HCl + NaOH  NaCl + HOH

Products of Neutralization HCl + NaOH  NaCl + H2O H2SO4 + Ca(OH)2  CaSO4 + 2 H2O HNO3 + KOH  KNO3 + H2O The products of neutralization are always a ______ and _______. salt water

Amphoteric When a substance acts like an acid under one set of conditions and as a base under another set of conditions.

The pH scale is a way of expressing the strength of acids and bases The pH scale is a way of expressing the strength of acids and bases. Instead of using very small numbers, we just use the NEGATIVE power of 10 on the Molarity of the H+ (or OH-) ion. Under 7 = acid 7 = neutral Over 7 = base

(Remember that the [ ] mean Molarity) Calculating the pH pH = - log [H+] (Remember that the [ ] mean Molarity) Example: If [H+] = 1 X 10-10 pH = - log 1 X 10-10 pH = - (- 10) pH = 10 Example: If [H+] = 1.8 X 10-5 pH = - log 1.8 X 10-5 pH = - (- 4.74) pH = 4.74

Calculating [OH-] from pH What is the [OH-] of a solution with pH = 4.95? First find [H3O+] 4.95 = -log [H3O+] [H3O+] = 10-4.95 [H3O+] = 1.12 x 10-5 Now solve for [OH-] [OH-] = 1 x 10-14 = 1.0 x 10-9 1.12 x 10-5 pH = -log[H3O+] 8.2 pH: A Measurement Scale for Acids and Bases 1 x 10-14 = [H3O+][OH-]

Try These! pH = - log [H+] pH = - log 0.15 pH = - (- 0.82) pH = 0.82 pH = - log 3 X 10-7 pH = - (- 6.52) pH = 6.52 Find the pH of these: 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

PROBLEM: You have 50. 0 mL of 3. 0 M NaOH and you want 0. 50 M NaOH PROBLEM: You have 50.0 mL of 3.0 M NaOH and you want 0.50 M NaOH. What do you do? Add water to the 3.0 M solution to lower its concentration to 0.50 M Dilute the solution!

But how much water do we add? PROBLEM: You have 50.0 mL of 3.0 M NaOH and you want 0.50 M NaOH. What do you do? But how much water do we add?

The important point is that ---> PROBLEM: You have 50.0 mL of 3.0 M NaOH and you want 0.50 M NaOH. What do you do? How much water is added? The important point is that ---> moles of NaOH in ORIGINAL solution = moles of NaOH in FINAL solution

Amount of NaOH in original solution = M • V = PROBLEM: You have 50.0 mL of 3.0 M NaOH and you want 0.50 M NaOH. What do you do? Amount of NaOH in original solution = M • V = (3.0 mol/L)(0.050 L) = 0.15 mol NaOH Amount of NaOH in final solution must also = 0.15 mol NaOH Volume of final solution = (0.15 mol NaOH)(1 L/0.50 mol) = 0.30 L or 300 mL

PROBLEM: You have 50. 0 mL of 3. 0 M NaOH and you want 0. 50 M NaOH PROBLEM: You have 50.0 mL of 3.0 M NaOH and you want 0.50 M NaOH. What do you do? Conclusion: add 250 mL of water to 50.0 mL of 3.0 M NaOH to make 300 mL of 0.50 M NaOH.

Preparing Solutions by Dilution A shortcut M1 • V1 = M2 • V2

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