1 - SCH3U1 - Acids and Bases Sections 10.1

2 Learning Goals 1.What is Arrhenius's definition of an acid? A base? 2.What is the Brønsted-Lowry definition of an acid? A base? 3.What do the terms "strong" and "weak" mean when applied to an acid or a base? 4.How are common acids and bases named? 5.How is an acidic anhydride formed? A basic anhydride?

3 Acids General Properties Acids are substances that exhibit the following properties when dissolved in water: –Acids taste sour. (Do NOT taste chemicals!) –Acids produce a stinging sensation on the skin when they enter an open wound. –Acids turn the color of the indicator dye litmus from blue to red. –Acids react with many metals, such as magnesium, zinc, and iron, to produce ionic compounds and hydrogen gas. –Acids react with bases, thereby losing their acidic properties.

Table 10.1 Common Acids 4

5 Bases General Properties Bases exhibit the following properties when dissolved in water: –Bases taste bitter. (Do NOT taste chemicals!) –Bases feel slippery or soapy on the skin. –Bases turn the color of the indicator dye litmus from red (pink) to blue. –Bases react with acids, thereby losing their basic properties.

6 Table 10.1 Common Bases

Conductivity of Strong Acids & Bases? 7

HCl = Strong Acid 8

Acetic Acid = Weak Acid 9

NaOH = Strong Base 10

Ammonia = Weak Base 11

Properties of Acids and Bases Taste Conductivity Feel Reaction with litmus paper Reaction with active metals Reaction with carbonate compounds 12

Properties of Acids and Bases 13

14

Arrhenius Theory 15

Arrhenius Theory How would the following acids dissociate in water according to Arrhenius? What is the recognizable PATTERN? HBr (aq)  HClO 4 (aq)  LiOH (aq)  Ba(OH) 2 (aq)  16

17 Arrhenius Theory In 1887 the Swedish chemist Svante Arrhenius proposed: –An acid is a substance that ionizes (breaks up into ions) in water to produce 1 or more H + ions –A base is a substance that dissociates in water to form 1 or more OH - ions

Let’s Use Arrhenius here… According to Arrhenius you have to have and H+ and an OH- in the base of an acid or base that is being dissociated to create an H+ or OH- in the products. This is not true! NH 3 (aq) + H 2 O (l)  NH 4 + (aq) + OH - (aq) 18 Limitations to Arrhenius Theory? We know NH3 is a base!

19 Limitations of Arrhenius Theory A free proton does not exist in water solutions. Polarity of water? Hydronium Ion H 3 O + – a hydrated proton, H H O:O: : + H + H H O : H + Water Hydrogen Ion (proton) Hydronium Ion

20 Brønsted-Lowry Theory These shortcomings were overcome by a theory proposed independently, in 1923, by J. N. Brønsted (Denmark) and T. M. Lowry (London) An acid is a proton donor A substance that gives up H+ (a proton). A base is a proton acceptor A substance that accepts H+ (a proton). TRANSFER OF A PROTON!!!

21 Brønsted-Lowry Examples Hydrogen Chloride in water is Hydrochloric acid

22 Brønsted-Lowry Examples Ammonia in water is a base

Conjugate Acid-Base Pairs By Brønsted-Lowry theory, the products of an acid base reaction are also acids and bases. An acid-base conjugate pair differs in structure only by a proton (H + ): CONJUGATE means “linked together” The conjugate acid of a species is that species plus a proton; The conjugate base of a species is that species minus a proton. CH 3 COOH + H 2 O H 3 O + + CH 3 COO - acidbaseconjugateconjugate acid base conjugateconjugate acid base acid base

24 Brønsted-Lowry Notes Like Arrhenius a Brønsted-Lowry acid must have a H+. *So all Arrhenius acids are also Brønsted- Lowry acids However, any negative anion species can be a Brønsted-Lowry base. (not only OH-)

25 Conjugate Pairs Examples Nitrous Acid HNO 2 (aq) + H 2 O H 3 O + + NO 2 - Conjugate Acid Base Pairs The conjugate base of HNO 2 is NO 2 -, the species that remains after HNO 2 loses a proton. acid base conjugate conjugate acid base

26 Conjugate Pairs Examples Ammonia NH 3 (aq) + H 2 O OH - + NH 4 + Conjugate Acid Base Pairs base acid conjugate conjugate base acid Notice acid-base pairs only differ by one proton (H+)

NH 3 (aq) + H 3 O + (l)

Arrhenius vs. Brønsted Lowry 28

29 Strong Acids Acids that are completely ionized in water solution are called strong acids.strong acids H 2 O HCl (g) -> H + (aq) + Cl - (aq) In mol/L HCl(aq) [H + ] = mol/L [Cl - ] = mol/L [HCl] = 0 mol/L Square Brackets indicates concentration All the HCl is dissociated in solution

30 Weak Acids Acids that are only partially ionized in aqueous solution are called weak acids.weak acids In 1.00 mol/L CH 3 COOH (aq) only about 1% of the molecules ionize, most of it remains as acetic acid molecules H 2 O CH 3 COOH (aq) H + (aq) + CH 3 COO - (aq) In mol/L CH 3 COOH (aq) [H 3 O + ] or [H + ] = mol/L [CH 3 COO - ] = mol/L [CH 3 COOH] = 0.99 mol/L

31 Monoprotic Acids One ionizable H atom per molecule –Hydrochloric Acid HCl –Hydrofluoric Acid HF –Nitric Acid HNO 3 –Hydrocyanic Acid HCN

32 Polyprotic Acids Diprotic Acids Two ionizable H atoms per molecule –Sulfuric Acid H 2 SO 4 –Carbonic Acid H 2 CO 3 Triprotic Acids Three ionizable H atoms per molucule –Phosphoric Acid H 3 PO 4

33 Not all Hydrogens are Acidic None of the hydrogens in methane (CH 4 ) are given up in acidic solution Only one hydrogen in acetic acid (C 2 H 4 O 2 ) is acidic, that is why it is often written as CH 3 COOH

34 How to tell the acidic hydrogens 1.We write a molecular formula with ionizable H atoms first. –HNO 3, H 2 SO 4, and H 3 PO 4 –HC 2 H 3 O 2, Ionizable Hydrogens Non-Ionizable Hydrogens

35 How to tell the acidic hydrogens 2.In organic chemistry, we often use formulas that show the ionizable hydrogen atoms last. Example carboxylic acids. Acetic acid CH 3 COOH Formic acid HCOOH Propionic acid CH 3 CH 2 COOH Butyric acid CH 3 CH 2 CH 2 COOH In each of these, only the H atom on the O atom is ionizable. Ionizable Hydrogens Non-Ionizable Hydrogens

36 Common Strong Acids Hydrochloric acid HCl (aq) Hydrobromic acid HBr (aq) Hydriodic acidHI (aq) Nitric acidHNO 3(aq) Sulfuric acidH 2 SO 4(aq) Perchloric acidHClO 4(aq)

37 Common Bases Bases produce OH - ions in aqueous solution (Arrhenius definition) –Group 1 and 2 cations with hydroxide ions Examples: NaOH Sodium Hydroxide (also known as lye) KOH Potassium Hydroxide Ca(OH) 2 Calcium Hydroxide (a.k.a. slaked lime) H 2 O NaOH (s)  Na + (aq) + OH - (aq) Strong bases are completely ionize in water: Strong Bases

38 Strong Bases Alkali metal hydroxides Lithium hydroxideLiOH (aq) Sodium hydroxideNaOH (aq) Potassium hydroxideKOH (aq) Rubidium hydroxideRbOH (aq) Cesium hydroxideCsOH (aq) Alkaline earth hydroxides Calcium hydroxideCa(OH) 2 (aq) Strontium hydroxideSr(OH) 2 (aq) Barium hydroxideBa(OH) 2 (aq)

39 Weak Bases Bases that are only partially ionized in aqueous solution are called weak bases.weak bases H 2 O NH 3 (g) + H 2 O NH 4 + (aq) + OH - (aq)

40 Ammonia as a proton acceptor Lone pair can be used to accept proton