Introduction to Acids, Bases

Arrhenius Definition of Acids and Bases Acids dissociate to produce H+ ions in aqueous (water) solutions HCl H+ (aq) + Cl- (aq) Bases dissociate to produce OH- ions in aqueous (water) solutions NaOH Na+ (aq) + OH-(aq)

Dissociation Dissociation: when a compound splits apart into ions in solution. How might these dissociate? H2SO4 KOH DO NOW: Packet page 3, #7 Practice Writing Dissociation Equations

Note: Acids and Bases are only reactive if their ions are dissociated (when aqueous) HCl (l) = hydrogen chloride HCl (aq) = hydrochloric acid

Getting to Know Some Acids

Some Common Acids See Table K HCl hydrochloric acid HNO3 nitric acid H3PO4 phosphoric acid H2SO4 sulfuric acid HC2H3O2 acetic acid 6

The Hydronium Ion (H30+) Acids produce the H+ ion This is just a “bare proton” and is very reactive. It immediately forms a coordinate covalent bond with nearby water molecules to form (H30+). Do Now: Draw the formation of the Hydronium Ion

Organic Acids Contain carbon Only one of the hydrogens is “acidic” and dissociates in solution Ex: Acetic Acid HC2H3O2 or CH3COOH

Naming Acids (Honors) Binary Acids Hydro __________ ic Acid (Contain 2 elements only) Ex: HCl, HBr, H2S, HF Hydro __________ ic Acid

Naming Acids (Honors) Ternary Acids Look at name of polyatomic ion (Contain hydrogen and a polyatomic ion) Do NOT start with “Hydro” Look at name of polyatomic ion If it ends in “ate” the acid ends in “ic” If it ends in “ite” the acid ends in “ous”

Name These Acids (Honors) HBr HNO3 H3PO4 HNO2 H2C2O4 HClO HBrO HClO4 H2S HIO3

Name These Acids (Honors) HBr = hydrobromic acid HNO3 = nitric acid H3PO4 = phosphoric acid HNO2 = nitrous acid H2C2O4 = oxalic acid HClO = hypochlorous acid HBrO = hypobromous acid HClO4 = perchloric acid H2S = hydrosulfuric acid HIO3 = iodic acid

Getting to Know Some Bases

Naming Bases All Arrhenius bases contain the hydroxide ion Name ends in “hydroxide” Ex: LiOH = lithium hydroxide Note: There are “Non” Arrhenius Bases, more on them later

Some Common Bases See Table L NaOH sodium hydroxide KOH potassium hydroxide Ba(OH)2 barium hydroxide Mg(OH)2 magnesium hydroxide Al(OH)3 aluminum hydroxide 15

C2H5OH for example is not a base. Important Note There are no “organic bases” (containing carbon). C2H5OH for example is not a base. It is an alcohol. The OH on this molecule does not dissociate to form OH- (hydroxide ion)

Salts “Salts” are ionic compounds that are not acids or bases. Metal cation (+) & nonmetal anion (-) Ex: NaCl, MgSO4, Li2S

Learning Check Acid, Base Name or Salt CaCl2 ______ _______________ KOH ______ _______________ Ba(OH)2 ______ _______________ HBr ______ _______________ H2SO4 ______ ________________ 18

Answers Acid,Base Name or Salt CaCl2 salt calcium chloride KOH base potassium hydroxide Ba(OH)2 base barium hydroxide HCl acid hydrochloric acid H2SO4 acid sulfuric acid

Electrolytes Acids & Bases & Salts are electrolytes Produce free ions when dissolved Solutions will conduct. More concentrated = more conductive. Do Now: Practice Ditto on Identifying Electrolytes http://www.kentchemistry.com/links/AcidsBases/Electrolytes.htm

Taste & Feel Acids: taste sour and give a burning sensation if touched Bases: taste bitter and feel slippery if touched DO NOT attempt to determine an acid or base by taste or touch ever in the lab!

Let’s Review Which substance, when dissolved in water, forms a solution that conducts an electric current? (1) C2H5OH     (3) C12H22O11 (2) C6H12O6     (4) CH3COOH

A solid substance was tested in the laboratory. The test results are listed below. • dissolves in water • is an electrolyte • melts at a high temperature Based on these results, the solid substance could be (1) Cu               (3) C (2) CuBr2          (4) C6H12O6

The compound HNO3 can be described as an (1) Arrhenius acid and an electrolyte (2) Arrhenius acid and a nonelectrolyte (3) Arrhenius base and an electrolyte (4) Arrhenius base and a nonelectrolyte

Based on Reference Table F, which of these salts is the best electrolyte? A. sodium nitrate B. magnesium carbonate C. silver chloride D. barium sulfate

A substance that conducts an electrical current when dissolved in water is called (1) a catalyst           (2) a non-electrolyte (3) a metalloid         (4) an electrolyte

Which compound is an Arrhenius acid? (1) CaO  (2) K2O (3) HCl   (4) NH3

When one compound dissolves in water, the only positive ion produced in the solution is H3O+(aq). This compound is classified as (1) a salt (2) a hydrocarbon (3) an Arrhenius acid (4) an Arrhenius base

Which substance is an Arrhenius acid? (1) Ba(OH)2            (2) H3PO4 (3) CH3COOCH3   (4) NaCl

Which compound releases hydroxide ions in an aqueous solution? (1) CH3COOH     (2) HCl (3) CH3OH           (4) KOH

An Arrhenius base yields which ion as the only negative ion in an aqueous solution? (1) hydride ion           (2) hydronium ion (3) hydrogen ion        (4) hydroxide ion

The compound NaOH(s) dissolves in water to yield (1) hydroxide ions as the only negative ions (2) hydroxide ions as the only positive ions (3) hydronium ions as the only negative ions (4) hydronium ions as the only positive ions

How are HNO3(aq) and CH3COOH(aq) similar? (1) They are Arrhenius acids and they turn blue litmus red. (2) They are Arrhenius acids and they turn red litmus blue. (3) They are Arrhenius bases and they turn blue litmus red. (4) They are Arrhenius bases and they turn red litmus blue.

Acids “Corrode” Certain Metals See Reference Table J Metals above Hydrogen on the table will react with acids to form a salt and H2 gas Single Replacement Reaction 2Zn(s) + 2HCl(aq) ZnCl2(aq) + H2(g)

Will an acid react with these metals? If so complete and balance the single replacement reaction. Mg + HNO3 Cu + HCl Ca + H2SO4

Answers Mg + 2HNO3 Mg(NO3)2 + H2 Cu + HCl No reaction Cu in below hydrogen on Table J Ca + H2SO4 Ca(SO4) + H2

Bases DO NOT corrode metals Interactive: Acid, Bases and Metals BBC (good for Indicators) http://www.bbc.co.uk/schools/ks3bitesize/science/chemical_material_behaviour/acids_bases_metals/activity.shtml DO NOW: Packet page 2 and 3, # 4, #5

pH Scale Used to help determine how acidic or basic something is. pH = 7 Neutral pH < 7 Acidic pH > 7 Basic

Acids & Bases Neutralize Each Other H+ ion and OH- ions will join together to form neutral water. Reaction is slightly exothermic (See Table I) H+ (aq) + OH- (aq) → H2O (l)

Determining if it is an Acid or Base How can you tell if something is acidic or basic?

Use an electronic pH meter

Use an indicator such as litmus

Use pH paper containing universal indicator

Acid/Bases Indicators Using Table M Litmus pH range for color change (4.5 – 8.3) Color change: red to blue Phenolphthalein (8 - 9) Color change: colorless to pink What color would these be if pH = 10? pH = 3?

Let’s Review Based on the results of testing colorless solutions with indicators, which solution is most acidic? (1) a solution in which bromthymol blue is blue (2) a solution in which bromcresol green is blue (3) a solution in which phenolphthalein is pink (4) a solution in which methyl orange is red

According to Reference Table M, what is the color of the indicator methyl orange in a solution that has a pH of 2? (1) blue         (2) orange (3) yellow     (4) red

Which indicator would best distinguish between a solution with a pH of 3.5 and a solution with a pH of 5.5? (1) bromthymol blue      (2) litmus (3) bromcresol green    (4) thymol blue

Which indicator is blue in a solution that has a pH of 5.6? (1) bromcresol green    (2) methyl orange (3) bromthymol blue   (4) thymol blue

Which indicator is yellow in a solution with a pH of 9.8? (1) methyl orange        (2) bromcresol green (3) bromthymol blue    (4) thymol blue

In which solution will thymol blue indicator appear blue? (1) 0.1 M CH3COOH    (2) 0.1 M HCl (3) 0.1 M KOH              (4) 0.1 M H2SO4

Properties of Acids (Summary) Produce H+ (as H3O+) ions in water Electrolytes (conduct in solution) Taste sour pH is < 7 Corrode metals (see Table J) React with bases to form salts and water (Neutralization)

Properties of Bases (Summary) Produce OH- ions in water Electrolytes (conduct in solution) Taste bitter, chalky pH is >7 Feel soapy, slippery React with acids to form salts and water (Neutralization)

Learning Check Describe the solution in each of the following as: 1) acid 2) base or 3)neutral. A. ___soda B. ___soap C. ___coffee D. ___ wine E. ___ water F. ___ grapefruit 53

Solution Describe each solution as: 1) acid 2) base or 3) neutral. A. _1_ soda B. _2_ soap C. _2_ coffee D. _1_ wine E. _3_ water F. _1_ grapefruit 54

Learning Check Identify each as characteristic of an A) acid or B) base ____ 1. Sour taste ____ 2. Produces OH- in aqueous solutions ____ 3. Chalky taste ____ 4. Is an electrolyte ____ 5. Produces H+ in aqueous solutions 55

Solution Identify each as a characteristic of an A) acid or B) base _A_ 1. Sour taste _B_ 2. Produces OH- in aqueous solutions _B_ 3. Chalky taste A, B 4. Is an electrolyte _A_ 5. Produces H+ in aqueous solutions 56