What are Acids and Bases? What are some common acids you know? What are some common bases you know? Where is it common to hear about ph balanced

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2 What are Acids and Bases? What are some common acids you know? What are some common bases you know? Where is it common to hear about ph balanced materials?

3 Historically, classified by their observable properties Acids: Have a sour taste like lemons or sour candy Corrode metals learned not to store vinegar or fruit juices in metal containers Changed blue litmus dye to red Bases: Bitter in taste Slippery in feel Changed red litmus dye to blue

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5 1. Arrhenius Definition: Experimented with electrolytes Aqueous solutions of acids and bases conduct electricity Therefore, the compounds were forming positive and negative ions in solution

6 Arrhenius Model of Acids An aqueous solution that produced hydrogen ions, H + Example: HCl (g) H + (aq) + Cl - (aq) Arrhenius Model of Bases An aqueous solution that produced hydroxide ions, OH - Example: NaOH (s) Na + (aq) + OH - (aq)

7 The Arrhenius model explains how acids and bases neutralize each other H + (aq) + OH - (aq) H 2 O (l) He did earn the 1903 Nobel Prize in Chemistry Insisting that the H + (aq) and OH - (aq) were important in acid and base behavior

8 Fundamental Problems: H + ion: essentially a proton with a small radius & positive charge Therefore, H + are unlikely to exist as free ions in aqueous solutions Instead they exist with surrounding water molecules resulting in: Hydronium ion, H 3 O + (aq) as we know them today

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10 Fundamental Problems: Assumes that all bases contain OH - ions Many ionic compounds (salts) have basic properties such as the ability to neutralize acids Examples: metal oxides, carbonates, fluorides, ammonia (NH 3 )

11 Binary Acids contain hydrogen and one other element Use: hydro ic acid Ex: HCl = hydrochloric acid Ex: H 2 S = hydrosulfuric acid

12 Oxyacids contain hydrogen and a poly atomic ion Use ending of ion for naming: -ite -ous acid I bite a delicous apple -ate -ic acid I ate something icky Ex: HNO 3 = nitric acid Ex: HNO 2 = nitrous acid Ex: HC 2 H 3 O 2 = acetic acid Ex: H 3 PO 3 = phosphorous acid

13 Strong Acid or Base: A strong electrolyte and completely ionizes or dissociates in water Weak Acid or Base: A weak electrolyte and only partially ionizes in water

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15 Examples: HCl hydrochloric acid: stomach acid, pools HBr hydrobromic acid H 2 SO 4 sulfuric acid: car battery acid, acid rain

16 Strong Bases: completely ionize in water Most of the common strong bases are the ionic hydroxides from group 1 and 2 metals. Dissociate completely win water to form OH - and the cation it was bonded to

17 Example: H 2 O NaOH (s) Na + (aq) + OH - (aq)

18 Examples: NaOH sodium hydroxide: drain cleaners KOH potassium hydroxide Mg(OH) 2 magnesium hydroxide: used in antacids

19 Examples: Acetic Acid (CH 3 CO 2 H) vinegar, sour wine Carbonic acid (H 2 CO 3 ) soda, blood Citric acid (H 3 C 6 H 5 O 7 ) fruit, soda

20 Examples: Ammonia (NH 3 ) glass cleaners Calcium carbonate (CaCO 3 ) antacids, minerals Calcium hypochlorite (Ca(OCl) 2 ) chlorine source for swimming pools

21 Brǿnsted-Lowry Acid: Any substance that can donate an H + ion to another substance Brǿnsted-Lowry Base: Any substance that can accept an H + ion from another substance

22 Polyprotic Acid: An acid containing more then one acidic hydrogen Examples: Phosphoric acid: H 3 PO 4 3 acidic hydrogens Carbonic acid: H 2 CO 3 2 acidic hydrogens Sulfuric acid: H 2 SO 4 2 acidic hydrogens

23 Polyprotic acids do not lose all their acidic hydrogen atoms in water to the same extent Example: Sulfuric Acid complete ionization. H 2 SO 4 (aq) + H 2 O (l) H 3 O + (aq) + HSO 4 - (aq) Once HSO 4 - (aq) forms, it also acts as an acid, but as a weak acid: HSO 4 - (aq) + H 2 O (l) H 3 O + (aq) + SO 4 2- (aq)

24 Lewis Acid: substance that is an electron pair acceptor To avoid bonding based on hydrogen BF 3 (aq) + F - (aq) BF 4 - (aq) Lewis Base: substance that is an electron-pair donor

25 Acid Base Arrhenius H + donor OH - donor Bronsted- Lowry p + donor p + acceptor Lewis e - pair acceptor e - pair donor

26 Conjugate Acid: The product that forms as a result of gaining an p + Conjugate Base: The product that forms as a result of losing an p + Example: HCl (g) + H 2 O (l) H 3 O + (aq) + Cl - (aq) acid base conjugate acid conjugate base

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28 Conjugate acid-base pairs always differ by one H + ion Conjugate acids has one more H + Has one more H atom in its formula Increase in charge by 1 Conjugate base has one less H + Has one less H atom in its formula Decrease in charge of 1

29 Amphoteric Substances: A substance that can act as either an acid or a base Examples: Water (most common) Acid: donates H + forming OH - Base: accepts H + forming H 3 O +

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32 Examples Bicarbonate ion, HCO 3 - Found in sodium bicarbonate, used to neutralize both acids and bases When mixed with a basic solution, it acts as an acid HCO - 3 (aq) + OH - (aq) CO 2-3 (aq) + H 2 O (l) acid conjugate base When mixed with an acidic solution, it acts as a base HCO - 3 (aq) + H 3 O + (aq) H 2 CO 3 (aq) + H 2 O (l) base conjugate acid

33 Strong acids completely dissociate to form H 3 O + and strong bases completely dissociate to form OH - HCl (aq) + NaOH (aq) NaCl (aq) + H 2 O (l) Neutralization reactions: a reaction where hyronium ions and hydroxide ions form water molecules Salt: ionic compound composed of a cation from a base and an anion from an acid

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35 Self-Ionization of Water Two water molecules interact to produce a hydronium ion and a hydroxide ion by proton transfer 2 H 2 O H 3 O + (aq) + OH - (aq) At 25 o C, 1 mole of hydronium and hydroxide ions exist in 10 7 liters of water Therefore: 1 mole ions = 1 x 10-7 M 10 7 L water

36 Water is neutral when the [H 3 O + ] = [OH - ] Water dissociation constant (K w ) constant rate at which water dissociates Different at each temperature K w = [H 3 O + ][OH - ] = [1 x 10-7 M][1 x 10-7 M] = 1 x M 2

37 ph: The negative logarithm (base 10) of the [H 3 O + ] Equation: ph = - log [H 3 O + ] Example: pure water ph = - log [H 3 O + ] ph = - log (1.0 x 10-7 ) ph = 7 Pure water has [H 3 O + ] = [OH - ] => ph = 7

38 Acidic solutions have ph < 7 Basic solutions have ph > 7

39 The ph and poh total is equal to ph + poh = This relationship allows us to determine the ph if the poh is known ph = poh = = 12.00

40 Some common substances, their ph and their [H 3 O + ] French: pouvior hyrogene, meaning hydrogen power

41 Consider the ph values of solutions that range in [H 3 O + ] from 1.0x10-1 M to 1.0x10-14 M Notice that the ph value = the exponent in the [H 3 O + ] but with a positive value Only allows for calculation if the [H 3 O + ] is a power of ten

42 Example: What is the ph of each of the following solutions? Once calculated, check to make sure you answer makes sense. A) M HBr B) M HNO 3 C) M KOH

43 Answer: A) M HBr HBr is a strong acid, which ionizes completely, so [H 3 O + ] = [HBr] ph = - log [H 3 O + ] ph = - log (0.0010) ph = 3.00 Acid!

44 Answer: B) M HNO 3 Nitric acid is also a strong acid, so the [H 3 O + ] = [HNO 3 ] ph = - log [H 3 O + ] ph = - log (0.035) ph = 1.46 Acid!

45 Answer: C) M KOH Potassium hydroxide is a strong base, which dissociates completely to form K + (aq) and OH - (aq) The [KOH] = [OH - ] = M In order to calculate ph, we need [H 3 O + ] [H 3 O + ] = K w _ = 1.0 x = 2.9 x M [OH - ] M

46 Answer: C) M KOH [H 3 O + ] = 2.9 x M ph = - log [H 3 O + ] ph = - log (2.9 x ) ph = Base!

47 If you can calculate the ph from your [H 3 O + ], can you do the reverse? Yes! How? Rearrange your parent equation! ph = - log [H 3 O + ] -ph = log [H 3 O + ] Inverse log (-ph) = [H 3 O + ] 10 -ph = [H 3 O + ]

48 Example: Olivia measures the ph of a soil sample solution to have a ph = 6.20, what is the [H 3 O + ]?

49 Answer: [H 3 O + ] = 10 -ph [H 3 O + ] = [H 3 O + ] = 6.3 x 10-7 M

50 If you can calculate the poh from your [OH - ], can you do the reverse? Yes! How? Rearrange your parent equation! poh = - log [OH - ] -poh = log [OH - ] Inverse log (-poh) = [OH - ] 10 -poh = [OH - ]

51 Example: Jake measured the ph of water in a swimming pool as What is the OH - concentration in the pool water?

52 Answer: Determine the poh from the ph ph + poh = poh = poh = 5.90

53 Answer: poh = 5.90 Then calculate the [OH - ] [OH - ] = 10 -poh [OH - ] = [OH - ] = 1.3 x 10-6 M

54 Several Methods: 1. ph Meter: Very accurate to within hundredths of a ph unit Measures the voltage that develops when electrodes are dipped into the solution

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57 2. ph Indicators or Litmus Strips: Less accurate but more convenient and cost friendly Brightly colored organic dyes that are weak acids or bases In solution they form an equilibrium with their conjugate bases Color of the indicator depends on whether the dye is in its acidic or basic form

58 2. ph Indicators or Litmus Strips: Ex) Phenolphthalein HIn (aq) + H 2 O (l) H 3 O + (aq) + In - (aq) colorless pink In the acidic form: HIn (aq) = colorless In the basic form: In - (aq) = pink Changes from colorless to pink between ph 8.2 and 10

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60 An indicator reveals if the ph of a solution is above or below a certain value Also disclose a specific ph within the indicators color-change range Subtle differences in hues are discernible at slightly different ph values

61 A mixture of indicators having a variety of colors and color-change ranges can be used to measure the ph of any solution Broad-range ph paper is treated with several indicators The user reads the ph by comparing the color the paper turns to a chart of reference colors and ph values

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63 The formation of water is quite common from the addition of hydrogen ion (H + ) and the hydroxide ion (OH - )

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65 Titration: The process of determining the concentration of one substance in a solution by reacting it with a solution of another substance that has a known concentration. Add the known substance until the reaction between the two substances is complete: equivalence point Shown by an indicator: changes color due to sensitivities of acids and bases End point: the point at which the indicator changes color

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69 Phenolphthalein

70 Molarity = moles / Liter M acid x V acid = M base x V base **Only true for a 1 to 1 mole ratio between the acid and base

71 Normality (N) number of equivalents of solute per liter of solution Equation: N = n * M normality = number of equiv * Molarity What is the molarity of a N Ca(OH) 2 soln? N = n * M N = 2 equiv * M M = M Ca(OH) 2

72 Chapter 14 p #15, 23, 24 Chapter 15 p #6, 9, 12, 15, 26, 31, 36