Acids and Bases

Characteristics of Acids Acids (ie HCl, H 2 SO 4, HCH 3 COO):  are ionic compounds in aqueous solution  react with many metals to form Hydrogen gas and a salt.  cause indicators to turn colour - Blue litmus turns red colourless - Pink Phenophthalein goes colourless  neutralize bases

Characteristics of Bases Bases (ie NaOH, Ca(OH) 2, NH 3 or NH 4 OH (aq) ):  are ionic compounds in aqueous solution  form when active metals react with water  cause indicators to turn colour - Red litmus turns blue - Colourless Phenophthalein goes pink  neutralize acids

Characteristics of Acids and Bases Both Acids and Bases: aare electrolytes ddissociate when put into aqueous solution aare reactive

The Arrhenius Theory of Acids and Bases Svante Arrhenius ( ) Suggested his theory to describe the activities of acids and bases when they were dissolved in water. He suggested that both acids and bases dissociate/ionize in aqueous solution. Science cracks me up!

The Arrhenius Theory of Acids and Bases Acids ionize to form H + ions. Examples: 1HCl (aq)  1H + (aq) + 1Cl - (aq) 1H 2 SO 4(aq)  1H + (aq) + 1HSO 4 - (aq)

The Arrhenius Theory of Acids and Bases Bases dissociate to form OH - ions. Examples: 1NaOH (aq)  1Na + (aq) + 1OH - (aq) 1Mg(OH) 2 (aq)  1Mg 2+ (aq) + 2OH - (aq)

The Arrhenius Theory of Acids and Bases Strengths of the Arrhenius Theory  It explains why acids and bases are electrolytes  It explains why acids and bases have different chemical properties. Limitations of the Arrhenius Theory  It does not explain why some compounds are acidic or basic in water.  For example NH 3 is basic in water and CO 2 is acidic in water.

Acid terminology….. Proton = H + = H 3 O + = hydronium ion

10 BrØnsted-Lowry Acids and Bases Since the Arrhenius theory does not work for all acids and bases, here is an alternate theory.

11 Br Ø nsted-Lowry Acids and Bases According to the Br Ø nsted-Lowry theory, acids donate a proton (H + ). bases accept a proton (H + ).

12 NH 3, a Br Ø nsted-Lowry Base In the reaction of ammonia and water, NH 3 is the base that accept H +. H 2 O is the acid that donates H +.

13 Conjugate Acid-Base Pairs In any acid-base reaction, there are two conjugate acid- base pairs. Each pair is related by the loss and gain of H +. One pair occurs in the forward direction. One pair occurs in the reverse direction. conjugate acid-base pair 1 HA + B A − + BH + conjugate acid-base pair 2

14 Conjugate Acids and Bases In this acid-base reaction, an acid, HF, donates H + to form its conjugate base, F −. a base, H 2 O, accepts H + to form its conjugate acid, H 3 O+. there are two conjugate acid-base pairs.

15 Conjugate Acid-Base Pairs In the reaction of HF and H 2 O, one conjugate acid-base pair is HF/F −. the other conjugate acid-base pair is H 2 O/H 3 O +. each pair is related by a loss and gain of H +.

16 Conjugate Acid-Base Pairs In the reaction of NH 3 and H 2 O, one conjugate acid-base pair is NH 3 /NH 4 + the other conjugate acid-base is H 2 O/H 3 O +.

17 Learning Check A. Write the conjugate base of the following. 1. HBr 2. H 2 S 3. H 2 CO 3 B. Write the conjugate acid of the following. 1. NO NH 3 3. OH -

18 Solution A. Remove H + to write the conjugate base. 1. HBrBr - 2. H 2 SHS - 3. H 2 CO 3 HCO 3 - B. Add H + to write the conjugate acid. 1. NO 2 - HNO 2 2. NH 3 NH OH - H 2 O

19 Learning Check Identify the sets that contain acid-base conjugate pairs. 1. HNO 2, NO 2 − 2. H 2 CO 3, CO 3 2− 3. HCl, ClO 4 − 4. HS −, H 2 S 5. NH 3, NH 4 +

20 Solution Identify the sets that contain acid-base conjugate pairs. 1. HNO 2, NO 2 − 4. HS −, H 2 S 5. NH 3, NH 4 +

21 Learning Check A. The conjugate base of HCO 3 − is 1. CO 3 2− 2. HCO 3 − 3. H 2 CO 3 B. The conjugate acid of HCO 3 - is 1. CO 3 2− 2. HCO 3 − 3. H 2 CO 3 C. The conjugate base of H 2 O is 1. OH − 2. H 2 O 3. H 3 O + D. The conjugate acid of H 2 O is 1. OH − 2. H 2 O 3. H 3 O +

22 Solution A. The conjugate base of HCO 3 − is 1. CO 3 2− B. The conjugate acid of HCO 3 − is 3. H 2 CO 3 C. The conjugate base of H 2 O is 1. OH − D. The conjugate acid of H 2 O is 3. H 3 O +

What factors affect Acid and Base strength? Acid strength is determined by the degree to which the acid ionized in water Strong Acid - the reaction below goes to completion. HCl (g)  H 1+ (aq) + Cl 1- (aq) Base strength is determined by the degree to which the base ionizes in water Strong Base – the reaction below goes to completion NaOH (s)  Na 1+ (aq) + OH 1- (aq)

What factors affect Acid and Base strength? The most important factor is the degree of ionization or dissociation of the acid or base Not all Acids and Bases are strong, for instance: A 1.00M HCl solution is a strong acid; A 1.00M CH 3 COOH solution is a weak acid. A 1.00M NaOH solution is a strong base; A 1.00M NH 4 OH solution is a weak base.

Strong Acids Ionize 100% (>99%) upon dissolving in water. Because the acid ionizes 100%, the concentration of H + is the same as the concentration of the acid. (ie a 1.00M solution of HCl has an [H + ] of 1.00M) Examples include only HCl, HBr, HClO 4, H 2 SO 4, HNO 3, HI Are very good electrolytes because of all of the ions in solution.

Strong Bases Dissociate 100% upon dissolving in water. The concentration OH - is the same as the concentration of the base. (ie a 1.00M solution of NaOH has an [OH - ] of 1.00M) Examples include oxides and hydroxides of Group 1 metals and Group 2 metals below beryllium. Are very good electrolytes because of all of the ions in solution.

Weak Acids Dissociate much less than 100% upon dissolving in water (less than 5% dissociation). The concentration H + is much less than the concentration of the acid. (ie a 1.00M solution of HCH 3 COOH has an [H + ] less than 1.00M) Examples include all of the other acids. Are very poor electrolytes because of the low concentration of ions in solution. CH 3 COOH (aq)  H 1+ (aq) + CH 3 COO 1- (aq)

Weak Bases Dissociate much less than 100% upon dissolving in water (less than 5% dissociation). Because the base dissociates 100%, the concentration OH - is much less than the concentration of the base. (ie a 1.00M solution of NH 4 OH has an [OH - ] less than 1.00M) Examples include all of the other bases. Are very poor electrolytes because of the low concentration of ions in solution. NH 4 OH (s)  NH 4 + (aq)+ OH - (aq)

General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.29 Calculating pH The pH Scale

pH of a Solution pH is a way of indicating the concentration of H+ ions present in a solution pH = Power of Hydrogen

General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.31 pH Scale The pH of a solution  is used to indicate the acidity of a solution  has values that usually range from 0 to 14  is acidic when the values are less than 7  is neutral with a pH of 7  is basic when the values are greater than 7

General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.32 pH of Everyday Substances

General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.33 Identify each solution as A) acidic, B) basic, or N) neutral ___ 1) HCl with a pH = 1.5 ___ 2) pancreatic fluid [H 3 O + ] = 1 x 10 −8 M ___ 3) Sprite soft drink, pH = 3.0 ___ 4) pH = 7.0 ___ 5) [OH − ] = 3 x 10 −10 M ___ 6) [H 3 O + ] = 5 x 10 −12 M Learning Check

General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.34 Identify each solution as A) acidic, B) basic, or N) neutral A 1) HCl with a pH = 1.5 B 2) Pancreatic fluid [H 3 O + ] = 1 x 10 −8 M A 3) Sprite soft drink pH = 3.0 N 4) pH = 7.0 A 5) [OH - ] = 3 x 10 −10 M B 6) [H 3 O + ] = 5 x 10 −12 Solution

General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.35 Testing the pH of Solutions The pH of solutions can be determined using  a pH meter  pH paper  indicators that have specific colors at different pH values

General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.36  Mathematically, pH is the negative log of the hydronium ion concentration pH = −log [H 3 O + ]  For a solution with [H 3 O + ] = 1 x 10 −4, pH = −log [1 x 10 −4 ] pH =  [  4.0] pH = 4.0 Calculating pH

General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.37 Significant Figures in pH When expressing log values, the number of decimal places in the pH is equal to the number of significant figures in the coefficient of [H 3 O + ]. coefficient decimal places [H 3 O + ] = 1 x 10 −4 pH = 4.0 [H 3 O + ] = 8.0 x 10 −6 pH = 5.10 [H 3 O + ] = 2.4 x 10 −8 pH = 7.62

General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.38 Guide to Calculating pH

General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.39 Find the pH of a solution with a [H 3 O + ] of 1.0 x 10 −3. STEP 1 Enter the [H 3 O + ] value: Enter 1 x 10  3 (press 1 EE 3, then change sign) The EE key gives the exponent of 10. STEP 2 Press log key and change the sign:  log (1 x 10 −3 ) =  [  3] STEP 3 Make the number of digits after the decimal point (2) equal to the number of significant figures in the coefficient (2): [H 3 O + ] = 1.0 x 10 −3 pH is 3.00 Example of Calculating pH

General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.40 Learning Check What is the pH of coffee if the [H 3 O + ] is 1 x 10 −5 M? 1) pH = 9.0 2) pH = 7.0 3) pH = 5.0

General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.41 Solution What is the pH of coffee if the [H 3 O + ] is 1 x 10 −5 M? STEP 1 Enter the [H 3 O + ] value: Enter 1 x 10  5 (press 1 EE 5, then change sign ) STEP 2 Press log key and change the sign:  log (1 x 10 −5 ) =  [  5] STEP 3 Make the number of digits after the decimal point (1) equal to the number of significant figures in the coefficient (1): [H 3 O + ]= 1 x 10 −5, pH is 5.0 (3)

General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.42 The [H 3 O + ] of tomato juice is 2 x 10 −4 M. What is the pH of the solution? 1) 4.0 2) 3.7 3) 10.3 Learning Check

General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.43 The [H 3 O + ] of tomato juice is 2 x 10 −4 M. What is the pH of the solution? STEP 1 Enter the [H 3 O + ] value: Enter 2 x 10  4 (press 2 EE 4, then change sign ) STEP 2 Press log key and change the sign:  log (2 x 10 −4 ) =  [  3.7] STEP 3 Make the number of digits after the decimal point (1) equal to the number of significant figures in the coefficient (1): [H 3 O + ] = 2 x 10 −4, pH is = 3.7 (2) Solution

General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc. pOH – power of hydroxide  pOH is the power of hydroxide and measures the log of the OH - concentration in a solution  You can calculate pOH the same way as pH except you use the [OH - ] in your calculation  pOH = -log [OH - ]  pH and pOH are related to each other through the pH scale  Since the pH scale is on a range of 14 points,  pH + pOH = 14  Therefore, if you know the pOH you can use it to find pH 44

General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.45 The [OH − ] of a solution is 1.0 x 10 −3 M. What is the pH? 1) ) ) –11.00 Learning Check

General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.46 The [OH − ] of a solution is 1.0 x 10 −3 M. What is the pH? STEP 1 find pOH pOH = -log [1.0 x ] = 3.00 STEP 2 find pH pH + pOH = 14 pH = 14 – pOH = 14 – 3.00 = STEP 3 Make the number of digits after the decimal point (2) equal to the number of significant figures in the [OH - ] (2): Solution

General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.47 [H 3 O + ], [OH - ], and pH Values

General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc. Calculating [H + ] from pH  The [H+] can be determined from the pH using the inverse log function  [H+] = 10 -pH 48

General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.49 Example 1: Calculating [H 3 O + ] from pH Calculate the [H 3 O + ] for a pH value of 8.0. [H 3 O + ] = 10 − pH For pH = 8.0, the [H 3 O + ] = 10 − 8 STEP1 Enter the pH value, change sign: –8.0 STEP2 Convert  pH to concentration: Use 2 nd function key and then10 x key or inverse key and then log key 1 − 08 STEP 3 Adjust the significant figures in the coefficient (1 digit following decimal point = 1 digit in the coefficient): [H 3 O + ] = 1 x 10 − 8 M

General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.50 Example 2: Calculating [H 3 O + ] from pH Calculate the [H 3 O + ] for a pH of STEP1 Enter the pH value, change sign: –3.80 STEP2 Convert  pH to concentration: Use 2 nd function key and then10 x key or inverse key and then log key − 04 STEP 3 Adjust the significant figures in the coefficient (2 digit following decimal point = 2 digit in the coefficient): [H 3 O + ] = 1.6 x 10 − 4 M

General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.51 What is the [H 3 O + ] of a solution with a pH of 10.0? 1) 1 x 10 − 4 M 2) 1 x M 3) 1 x 10 − 10 M Learning Check

General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.52 What is the [H 3 O + ] of a solution with a pH of 10.0? STEP1 Enter the pH value, change sign: –10.0 STEP2 Convert  pH to concentration: Use 2 nd function key and then10 x key or inverse key and then log key 1 − 10 STEP 3 Adjust the significant figures in the coefficient (1 digit following decimal point = 1 digit in the coefficient): [H 3 O + ] = 1 x 10 − 10 M (3) Solution

General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.53 What is the [H 3 O + ] of a solution with a pH of 2.85? 1) 1.0 x 10 − 2.85 M 2) 1.4 x 10 − 3 M 3) 8.5 x 10 − 2 M Learning Check

General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.54 What is the [H 3 O + ] of a solution with a pH of 2.85? STEP1 Enter the pH value, change sign: –2.85 STEP2 Convert  pH to concentration: Use 2 nd function key and then10 x key or inverse key and then log key = x 10 − 03 STEP 3 Adjust the significant figures in the coefficient (2 digits following decimal point = 2 digits in the coefficient): [H 3 O + ] = 1.4 x 10 − 3 M (2) Solution