Acids and Bases

Acid and Base Definitions 19.1

Acid Properties Water solutions of acids conduct electricity Water solutions of acids conduct electricity Acids often react with metal to produce hydrogen gas Acids often react with metal to produce hydrogen gas Acids change color indicators Acids change color indicators Acid + Base → Salt + Water Acid + Base → Salt + Water Acids have sour taste—don’t try this Acids have sour taste—don’t try this Acids react with carbonates to produce carbon dioxide Acids react with carbonates to produce carbon dioxide Acids sting skin Acids sting skin

Bases Water solutions of bases conduct electricity Water solutions of bases conduct electricity Bases change color indicators Bases change color indicators Acid + Base → Salt + Water Acid + Base → Salt + Water Bases have a bitter taste—don’t try this Bases have a bitter taste—don’t try this Bases react with fat to make soap Bases react with fat to make soap Bases have slippery feel Bases have slippery feel Strong bases are caustic to skin Strong bases are caustic to skin

The pH scale. pH = -log [H+] Examples: 1.Find the pH of a solution if the hydrogen ion concentration is 0.027M. 2.Find the pH of a solution where 0.03 moles of HCl is dissolved into 0.2 liters of water.

13Oven Cleaner/Drano 12 Hair remover 11 Ammonia 10 Soap 9Baking Soda, bleach, antacids 8Shampoo 7Water, blood, eggs, baby shampoo 6Urine, milk, saliva 5Coffee, bread, rainwater 4Tomatoes 3Vinegar, soda, beer 2Stomach acid, lemon juice 1Battery acid pH pH of Various solutions

Acid & Base Strength Strong acids and bases completely ionize (separate) in solution Strong acids and bases completely ionize (separate) in solution Acids: Nitric, sulfuric, hydrobromicAcids: Nitric, sulfuric, hydrobromic Bases: sodium hydroxide, potassium hydroxideBases: sodium hydroxide, potassium hydroxide Weak acids and bases slightly ionize Weak acids and bases slightly ionize Acids: Acetic, carbonic, hydrofluoricAcids: Acetic, carbonic, hydrofluoric Bases: Ammonium hydroxideBases: Ammonium hydroxide

Common Aqueous Acids Chapter 14 Section 1 Properties of Acids and Bases

Acid and Base Types Monoprotic acids Monoprotic acids HClHCl Monobasic bases Monobasic bases NaOHNaOH Diprotic Acid Diprotic Acid H 2 SO 4, H 2 CO 3H 2 SO 4, H 2 CO 3 Triprotic Acid Triprotic Acid H 3 PO 4H 3 PO 4 Dibasic Bases Dibasic Bases Ca(OH) 2, Mg(OH) 2Ca(OH) 2, Mg(OH) 2 “polyprotic”

19.1 Acids and Bases Hydrochloric Acid Hydrochloric Acid

© 2009, Prentice- Hall, Inc. Some Definitions Arrhenius Arrhenius An acid is a substance that, when dissolved in water, increases the concentration of hydrogen ions.An acid is a substance that, when dissolved in water, increases the concentration of hydrogen ions. HCl → H + + Cl - HCl → H + + Cl - A base is a substance that, when dissolved in water, increases the concentration of hydroxide ions.A base is a substance that, when dissolved in water, increases the concentration of hydroxide ions. NaOH → Na + + OH - NaOH → Na + + OH -

© 2009, Prentice- Hall, Inc. Brønsted-Lowry Theory of Acids and Bases An acid is a proton donor. An acid is a proton donor. A base is a proton acceptor. A base is a proton acceptor. HCl + H 2 O → H 3 O + + Cl - HCl + H 2 O → H 3 O + + Cl - HCl is an acid because it donates a proton to water. HCl is an acid because it donates a proton to water. Hydronium Ion: H 3 O + Hydronium Ion: H 3 O + This is a hydrated protonThis is a hydrated proton

Brønsted-Lowry Theory of Acids and Bases An acid is a proton donor. An acid is a proton donor. A base is a proton acceptor. A base is a proton acceptor. Na 2 CO 3 is a Bronsted-Lowry base because the carbonate ion accepts a proton from water. Na 2 CO 3 is a Bronsted-Lowry base because the carbonate ion accepts a proton from water. Water is an acid because it donates a proton to the carbonate ion. Water is an acid because it donates a proton to the carbonate ion. CO H 2 O ↔ OH - + HCO 3 - Notice that we ignore the sodium ion because it is neutral. Notice that we ignore the sodium ion because it is neutral. © 2009, Prentice- Hall, Inc.

Why Ammonia is a Base?

Brønsted-Lowry Acids and Bases A water molecule that gains a hydrogen ion becomes a positively charged hydronium ion (H 3 O + ). A water molecule that gains a hydrogen ion becomes a positively charged hydronium ion (H 3 O + ). 19.1

© 2009, Prentice- Hall, Inc. Lewis Acids Lewis acids are defined as electron-pair acceptors. Lewis acids are defined as electron-pair acceptors. Atoms with an empty valence orbital can be Lewis acids. Atoms with an empty valence orbital can be Lewis acids.

© 2009, Prentice- Hall, Inc. Lewis Bases Lewis bases are defined as electron-pair donors. Lewis bases are defined as electron-pair donors. Anything that could be a Brønsted-Lowry base is a Lewis base. Anything that could be a Brønsted-Lowry base is a Lewis base. Lewis bases can interact with things other than protons, however. Lewis bases can interact with things other than protons, however.

Acid and Base Definitions 19.1

A conjugate acid-base pair consists of two substances related by the loss or gain of a single hydrogen ion.A conjugate acid-base pair consists of two substances related by the loss or gain of a single hydrogen ion Conjugate Acid-Base Pairs

19.1

Conjugate Acids and Bases The species that remains after a Brønsted- Lowry acid has given up a proton is the conjugate base of that acid. Chapter 14 acid conjugate base

Conjugate Acids and Bases, continued Brønsted-Lowry acid-base reactions involve two acid-base pairs, known a conjugate acid-base pairs. Chapter 14 acid 1 base 2 base 1 acid 2

Conjugate Acids and Bases, continued Strength of Conjugate Acids and Bases The stronger an acid is, the weaker its conjugate base The stronger a base is, the weaker its conjugate acid Chapter 14 strong acid base acid weak base

Conjugate Acids and Bases Strength of Conjugate Acids and Bases Proton transfer reactions favor the production of the weaker acid and the weaker base. Chapter 14 stronger acid stronger base weaker acid weaker base The reaction to the right is more favorable weaker acid weaker base stronger acid stronger base The reaction to the left is more favorable

Relative Strengths of Acids and Bases

Amphoteric Compounds Any species that can react as either an acid or a base is described as amphoteric. example: water water can act as a base acid 1 base 2 acid 2 base 1 water can act as an acid base 1 acid 2 acid 1 base 2

Oxyacids of Chlorine Chapter 14 Section 3 Acid-Base Reactions

pH pH = -log [H + ] (acid concentration) pH = -log [H + ] (acid concentration) pOH = -log [OH - ] (base concentration) pOH = -log [OH - ] (base concentration) For aqueous solutions at 25 °C: For aqueous solutions at 25 °C: [H + ] [OH - ] = 1.0 x = K w[H + ] [OH - ] = 1.0 x = K w This is called the “ion product constant” for water This is called the “ion product constant” for water pH + pOH = 14pH + pOH = 14

19.2

Measuring pH Universal Indicators Universal Indicators 19.2

Measuring pH 19.2

Neutralization Reactions Chapter 14

Amphoteric Compounds, continued –OH in a Molecule The covalently bonded IOH group in an acid is referred to as a hydroxyl group. Molecular compounds containing —OH groups can be acidic or amphoteric. The behavior of a compound is affected by the number of oxygen atoms bonded to the atom connected to the —OH group. Section 3 Acid-Base Reactions

Other Acid Base Facts Water is able to self ionize Water is able to self ionize H 2 O + H 2 O  H 3 O + + OH - When H+ ion are in solution, they always join with a water molecule to form a hydronium ion When H+ ion are in solution, they always join with a water molecule to form a hydronium ion H + + H 2 O  H 3 O + H + + H 2 O  H 3 O +

K a Acid Ionization Constant K a = [H + ] [A - ] [HA] A 0.1M solution of ethanoic acid is found to have [H+]=4.2 x Calculate the acid dissociation constant. K a = [H + ] [A - ] [HA] K a = (4.2 x )(4.2 x ) = 1.8 x x x 10 -3

Buffer Solutions Solutions that resist change in pH when acids or bases are added to them. Solutions that resist change in pH when acids or bases are added to them. Formed by mixing a weak acid and its salt Formed by mixing a weak acid and its salt HC 2 H 3 O 2 + NaC 2 H 3 O 2HC 2 H 3 O 2 + NaC 2 H 3 O 2 When NaOH is added to the solution, HC 2 H 3 O 2 reacts and consumes the OH - ions When NaOH is added to the solution, HC 2 H 3 O 2 reacts and consumes the OH - ions When HCl is added to the solution, the H + ions react with the acetate ions from the salt When HCl is added to the solution, the H + ions react with the acetate ions from the salt Results: buffer solution resist changes in pH! Results: buffer solution resist changes in pH! Buffer solutions are important in maintaining blood pH. Buffer solutions are important in maintaining blood pH.

Amphoteric Substances Substances that can act as acids or bases Substances that can act as acids or bases Remember:Remember: Acids are proton donors Acids are proton donors Bases are proton acceptors Bases are proton acceptors Ex. Bisulfate ion: HSO 4 - Ex. Bisulfate ion: HSO 4 - HSO H + → H 2 SO 4 HSO H + → H 2 SO 4 HSO OH - → H 2 O + SO 4 2- HSO OH - → H 2 O + SO 4 2-

19.2

Titration Titration is the process of determining the concentration of an unknown solution through volumetric analysis Titration is the process of determining the concentration of an unknown solution through volumetric analysis When an acid and base are mixed, for neutralization to occur: When an acid and base are mixed, for neutralization to occur: n A =n B M acid x V acid = M base x V base

Microscopic view of the solutions in the titration of M HNO 3 with M NaOH.

End point is when the color change occurs Macid x Vacid = Mbase x Vbase 0.2M x 50mL = 0.1M x Vbase Vbase = 100mL The pH curve for the titration of 50.0 mL of M HNO 3 with M NaOH.

Titration Problems A solid mixture contains NaOH and NaCl. If 10 ml of 0.1 M HCl is required to titrate a 0.1 g sample of this mixture to its end point, what is the percent NaOH in the sample? 1 mole of HCl neutralizes 1 mole of NaOH 1 mole of HCl neutralizes 1 mole of NaOH How many moles of HCl are required to complete titration How many moles of HCl are required to complete titration

Titration Problems 20 ml of an aqueous base Ca(OH) 2 is used in titration with a color indicator. If 25 ml of 0.05M HCl is required to reach the end point, what is the concentration of the Ca(OH) 2 ? 20 ml of an aqueous base Ca(OH) 2 is used in titration with a color indicator. If 25 ml of 0.05M HCl is required to reach the end point, what is the concentration of the Ca(OH) 2 ? Balance Equation: Balance Equation: 2HCl + Ca(OH) 2 → CaCl 2 + 2H 2 O moles of acid = 2 x moles of base moles of acid = 2 x moles of base Therefore M acid x V acid = 2 x M base x V baseTherefore M acid x V acid = 2 x M base x V base

Titration Curve for NaOHand HCL pH Volume HCl