Acids and Bases An Introduction
Introduction • Inorganic and organic acids are important industrial chemicals; in 2002, H2SO4 was the number 1 chemical produced in the U.S.: 36,000,000 metric tons (80,000,000,000 lbs) 1metric ton = 1000Kg = 2204.6lbs
Common Household Acids Some common household acids: • Vinegar CH3COOH • Citric acid • Ascorbic acid
Common Household Bases Some common household bases: • Ammonia - NH3 (cleaners) • Sodium hydroxide – NaOH (oven cleaner and drain cleaner) • Calcium oxide – CaO (cement)
Physical Properties Physical properties of acids: • Sour/tart taste • Pricking/stinging sensation on the skin • blue to red litmus paper Physical properties of bases: • Bitter taste • Slippery to touch • red to blue litmus paper
Acid Base Theories The great theorists
Definitions of Acids and Bases Arrhenius Acid: produce H+ in water Base: produce OH- in water NaOH sodium hydroxide HCl hydrochloric acid
Definition of Acids and Bases Brondsted-Lowry Acid: donates a proton Base: accepts a proton H+, H has no neutrons so this is a proton
Definition of Acids and Bases Lewis Acid: electron pair acceptor Base: electron pair donor BF3 F NH3 H F : B H : N: F H Can accept e- Can donate e-
For the equation: HX (aq) H+ (aq) + X- (aq) HX is the acid For example HCl (aq) H+ (aq) + Cl – (aq) In strong acids, this reaction goes to completion (only products are left)
Equilibrium Ka = [H+][Cl-] [HCl] Ka is the equilibrium constant for acids [ ] means concentration in moles/liter or Molarity For strong acids, the Ka is so large that is cannot be measured, because the acids completely, totally dissociates
Strong Acids The Big 6 Acids: • HCl hydrochloric acid • H2SO4 sulfuric acid • HNO3 nitric acid • H3PO4 phosphoric acid • HF hydrofluoric acid • HClO4 Perchloric acid
Weak Acids Have Ka < 1 HSO4- hydrogen sulfate ion 1.2 x 10 -2 HClO2 chlorous acid 1.2 x 10 -2 HNO2 nitrous acid 4.0 a 10 -4 HCN hydrocynaic acid 6.2 x 10 -10 NH4+ ammonium ion 5.6 z 10 -10 HOC6H5 phenol 1.6 x 10-10 Note: Bases are very weak acids
Strong Bases Strong Bases are like strong acids: they dissociate completely HB B+ + OH- For example KOH K+ + OH-
Weak Bases The Kb is just like the Ka Kb = [K+][OH-] [KOH] Kb is the equilibrium constant of a base [ ] is concentration in Molarity (mole/liter)
Measuring Concentration of Hydrogen pH = -log [H+] Find the pH if [H+] = 1.00 x 10-5 How about the pH if the [H+] = 5.43 x 10-3 pOH = - log [OH-] Find the pOH if [OH-] = 3.78 x 10 -8 How about the pOH if [OH-] = 8.99 x 10 -2 What would the pH of each of these be?
pH Scale http://www.youtube.com/watch?v=3otQdpMfiRg http://www.youtube.com/watch?v=YvnwiP1u8-A
Acid-Base Indicators Common Indicators: Phenolphtalein pink in base, clear in acid Litmus Paper red blue bluered Bromthymol blue pH 3 green pH 4.5 blue Methyl red pink in acid, yellow in base There is an indicator for every purpose http://www.youtube.com/watch?v=vrOUdoS2BtQ
pH Meter • pH meters, unlike indicators, directly measure the concentration of H+ ions. They do this by measuring the electrical conduction of the solution. • Why will the solution with more H+ conduct electricity better?
Acid Nomenclature Binary Acids Prefix hydro- suffix -ic HCl hydrochloric HI hydroiodic HS hydrosulfuric
Acid Nomenclature Ternary Common form --ic HSO4, HClO3, HNO3 Sulfuric, chloric and nitric One fewer oxygen -ous Two fewer oxygen hypo-- and -ous One more oxygen per- and --ic
Acid Base Reactions Salts are produced by an acid/base neutralization: 2HCl + Ca(OH)2→ 2H2O + CaCl2 ← salt H2SO4 + 2NaOH → Na2SO4 + 2H2O salt What is a salt?? pH = -log[H+] 10-[H+] pH < 7 = acidic pH 7 > = basic pH = 7 = neutral http://www.youtube.com/watch?v=PCM5IwJ8wcs
Acid-Base Titrations Titrations are done to find the molarity of the acid or the base. A buret(a long graduated cylinder ) is attached to the ring stand with a buret clamp. Liquid can be delivered by turning the stopcock. http://www.youtube.com/watch?v=sFpFCPTDv2w&feature=related
Setting up a titration Usually the acid is placed in the flask with an indicator that will change color at pH = 7. Phenolphthalein is often used. Why is phenolphthalein a good choice?
Filling the buret After rinsing with both deionized water and base, base is placed in the buret. Why is this done over the sink?
Filling the buret Open the stopcock and let the base level drop to the top line (zero line) on the buret.
Reading the buret • The buret is graduated so that the amount of base delivered can be easily measured. • Read it as you would a graduated cylinder (at eye level, from the bottom of the meniscus)
Doing the titration The base is slowly added to the acid while mixing,
Finding the endpoint until the solution hits the endpoint. Note that the solution is barely pink. A dark pink means that too much base has been added.
Acid-Base Titration Calculations If we used 20 ml of 3.0 M HCl, how many ml of 3.0 M NaOH would we expect to need? HCl + NaOH NaOH + H2O 20 ml 3 mol 1 mol NaOH 1 L = 20 ml 1 L 1 mol HCl 3 mol
Acid-Base Titrations • So, what if you use 24.5 ml of 0.15 M NaOH to neutralize 50.0 ml of 2.5 M H2SO4? What is the concentration of the NaOH? • 2NaOH + H2SO4 Na2SO4 + 2H2O • 50.0 ml 2.5 mol 2 mol NaOH 1 L • 1 L 1 mol H2SO4 24.5 ml • What unit will the answer be in? • How many sig figs can we report?
What is Acid Rain? http://www.youtube.com/watch?v=HE6Y0iEuXMQ SO2 and NO2/NO3 from industry and cars Produce H2SO4 and HNO3 when combined with water Can fall as rain, snow and as solid deposition Acid Rain
What are the effects? • Forrest depletion: tree death • Can be seen in NH in White Mountains Clear lakes due to acid rain: clear because No plants or fish or other life is in the lake
Statues like this one, show corrosion due to acid rain. • Copper and marble are both acted on by acid
Effects of Acid Rain • Maple sugar production in the Northeast may be down due to acid rain: this is projected to continue • Car paints have had to be reformulated and there are many products on the market to repair damage