Acids and Bases

What are we going to discuss? Acids and Bases are classes of compounds that can be recognized by their easily observed properties. In this unit will learn about these properties, the definitions that are used to explain these properties, and the important reactions that occur between acids and bases.

Properties of Acids Electrolytes, or break up into ions when aqueous, conduct electricity in aqueous solutions Strong acid: good conductor Weak acid: poor conductor Sour Taste; citric acid and acetic acid React with most metals to produce H2 (g) React with bases to form H2O and salt React with indicators to change color turn litmus red phenolphthalein turns colorless pH values are 0.0-6.0

Properties of Bases Electrolytes conduct electricity in aqueous solutions Strong base: good conductor Bitter Taste; caustic, feel slippery (soap) React with acids to form H2O and salt React with indicators to change color litmus turns blue phenolphthalein turns pink --pH values are 7.1-14

Arrhenius’ Theory on Acids and Bases Arrhenius Acid Definition: a substance that ionizes in water to give hydrogen ions (proton) or a Hydronium ion: H+ or H3O+ Ex: Hydrochloric acid, HCl (a strong acid). HCl (g) H+ (aq) + Cl- (aq) ACIDIC solutions are formed when an acid transfers a proton to water.

Hydronium Ion The H+ interacts strongly with a lone pair of electrons on the oxygen of a water molecule. The resulting ion, H3O+ is called the hydronium ion. Ex: HCl + H2O H3O+1 + Cl-1

Arrhenius’ Bases Definition: a substance that ionizes in water to give hydroxide ions: OH- Example: NaOH, NH3 NaOH (s)  Na+(aq) + OH- (aq) NH3 +H2O  NH4+1 + OH-

SALTS A salt is an ionic compound that does not produce an H+ ion or OH- ion when dissolved in water. Salts are not acids or bases they are neutral substances. Ex. NaCl MgCl2

Naming Acids

Binary acids –two elements - H+ * hydrogen _____ ide becomes hydro_____ic acid Hydro_____ic acid Hydrochloric acid Hydrofluoric acid Hydrosulfuric acid Hydrobromic acid Hydrogen _____ ide Hydrogen chloride Hydrogen fluoride Hydrogen sulfide Hydrogen bromide

Ternary acids 3 elements: H+ and a polyatomic ion Hydrogen _____ate becomes _________ic acid Hydrogen _____ate Hydrogen sulfate Hydrogen chlorate Hydrogen nitrate Hydrogen phosphate _________ic acid Sulfuric acid chloric acid nitric acid Phosphoric acid

Hydrogen ________ite _________ ous acid Hydrogen _____ite becomes _______ous acid _______ous acid Nitrous acid Sulfurous acid Chlorous acid Hydrogen _____ite Hydrogen nitrite Hydrogen sulfite Hydrogen chlorite

Common Acids & Bases These two tables list the most common acids and bases. The first table lists common acids you will need to be familiar with. The second table lists common bases, these bases are the major bases you will need to be familiar with.

Strengths of Acids Strong acids: ionize completely which means if 100 molecules dissolve in water all 100 will break up into ions Examples: HCl  H+ + Cl- H2SO4  2H+ + SO4-2

Strengths of Acids Weak acids: ionize slightly or only a small percentage will break up into ions Example: acetic acid (vinegar) CH3COOH  CH3COO- + H+ ****note if an organic compound ends in COOH it’s a weak acid!!!

Strengths of Bases Strong bases: ionize completely Example: NaOH  Na+ +OH-

Strengths of Bases Weak base: ionizes slightly Example: ammonia NH3 + H2O  NH4+ + OH-

Acid and Base Reactions You will need to be familiar with 2 reactions that involve acids and bases. The first reaction only involves an acid with a metal. The second reaction deals with reacting an acid with a base to produce a salt and water or neutralization.

Acids with metals Some metals will replace the hydrogen in the acid and form hydrogen gas Single Replacement Reaction (SRR) Use Table 11.2 on p. 333 to find the reactivity chart to decide if the metal is more reactive or to see if the reaction will work. MgCl2 + H2 Mg + HCl

Neutralization Reaction In a neutralization reaction an Acid will react with a base to produce salt and water. Three ways we can express neutralization reactions: Word equation Formula equation Net ionic equation A net ionic equation has only the ions that have taken part in the reaction. In the reaction the ions that do not change are omitted, these ions are called spectator ions. See example

Neutralization acid + base water + a salt HCl + NaOH HOH + NaCl Hydrochloric Acid + Sodium Hydroxide yields Water + Sodium Chloride HCl + NaOH HOH + NaCl H+(aq) + Cl-(aq) + Na+(aq) + OH-(aq) H2O + Na+(aq) + Cl-(aq) H+(aq) + OH-(aq) H2O This is the net ionic equation for all neutralization reactions this equation shows how the ions are neutralized.

Try This One H2SO4 + 2NaOH 2H2O + Na2SO4 Sulfuric acid + sodium hydroxide yields water + sodium sulfate H2SO4 + 2NaOH 2H2O + Na2SO4 2H2O + 2Na+ + SO4-2 2H+ + SO4-2 + 2Na+ + 2OH- H+ + OH- H2O

Concentration of H+ in Acids A. 1.0 M HCl (monoprotic acid) HCl  H+ + Cl- Produces 1 H+ so the concentration of H+ is 1.0 M [H+] = 1.0 M

Concentration of H+ in Acids B. 1.0 M H2SO4 (diprotic acid) H2SO4  2H+ + SO4-2 Produces 2 H+ so the concentration of H+ is 2(1.0 M) [H+] = 2.0 M

Concentration of OH- in Bases A. 1.0 M KOH KOH  K+ + OH- Produces 1 OH- so the concentration of OH- is 1.0 M. [OH-] = 1.0 M

Concentration of OH- in Bases B. 1.0 M NaOH NaOH  Na+ + OH- Produces 1 OH- so the concentration of OH- is 1.0 M. [OH-] = 1.0 M

Concentration of OH- in Bases C. 1.0 M Ca(OH)2 Ca(OH)2  Ca+2 + 2OH- Produces 2 OH- so the concentration of OH- is 2(1.0 M). [OH-] = 2.0 M

Concentration of OH- in Bases D. 1.0 M Mg(OH)2 Mg(OH)2  Mg+2 + 2OH- Produces 2 OH- so the concentration of OH- is 2(1.0 M). [OH-] = 2.0 M

Titration An Acid-Base titration is a lab technique used find the unknown concentration of a specific volume for an acid or a base by neutralizing it with a specific volume of an acid or base of a known concentration. During a titration you deliver known volumes of a base to a known volume of an acid until it is neutralized or just slightly basic. This is also known as the endpoint of a titration. End point: point at which the solution changes from acidic to “just” basic. Using the Acid-Base titration formula listed on the next slide, you can solve for your unknown concentration.

MaVa = MbVb Acid- Base Titrations Ma = molarity of H+ Acids and bases neutralize each other when the concentration of the H+ equals the concentration of the OH-. MaVa = MbVb Ma = molarity of H+ Va = volume of acid Mb = molarity of OH- Vb = volume of base

Titration-Setup

Titrations (Neutralization) Problems Ex. What volume of 0.50M HCl is required to neutralize 100mL of 2.0M NaOH? MaVa = MbVb Ma = .5M Va = ?? Mb = 2.0M Vb = 100mL Plug in and solve 0.5(x) = 2.0(100) X = 400mL HCl Try the rest on your own!!!

Acidity and Alkalinity of Solutions Although water is a covalently bonded substance it does ionize to a very small extent as shown by the equation below. H2O   H+ + OH- It can be seen that in pure water the [H+] = [OH-]. When one of the ion concentrations increases the other will decrease.

Acidity and Alkalinity of Solutions (continued) So if you dissolve HCl in water the concentration of [H+] will increase and the [OH-] will decrease making the solution acidic. When NaOH is dissolved in water the concentration of [OH-] increases and the [H+] decreases making the solution basic. So when [H+] > [OH-] the solution is acidic and when [H+] < [OH-] the solution is basic. The terms acidity and alkalinity (or basicity) refer to the strength of the acid or base in terms of H+ and OH- concentrations.

Summary of Aqueous Solutions Autoionization of water HOH H+ + OH- In any aqueous [H+] x [OH-] = 1.0x10-14 Neutral Solution [H+] = [OH-] 1.0x10-7M = 1.0x10-7M Acidic Solution [H+] > [OH-] 1.0x10-1M > 1.0x10-13M Basic Solution [H+] < [OH-] 1.0x10-13M < 1.0x10-1M

pH Scale A scale, called the pH scale, has been developed to express [H+] as a number from 0 to 14. A pH of 0 is strongly acidic, a pH of 7 is neutral, and a pH of 14 is strongly basic The pH scale is logarithmic which means each change of a single pH unit signifies a tenfold change in the concentration of the [H+]

pH Scale (continued) Thus a solution with a pH of 5 is ten times greater in [H+] than a solution with a pH of 6 Because the [H+] and [OH-] are directly related, a pH change of one unit represents a tenfold increase or decrease of both [H+] and [OH-] As the concentration of the hydrogen ion increases the hydroxide ion concentration decreases and vice versa.

pH Scale

Acid – Base Indicators An indicator is a substance that changes its color when it gains or loses a proton or an H+ ion. There are several different indicators and they change differently when exposed to different pH values. On your reference tables there is a list of common acid base indicators that show the color changes at varying pH values You can use more than one indicator to estimate the approximate pH of an unknown substance from the color changes

BrØnsted-Lowry Acids & Bases Another theory on acids and bases defines an acid as any substance that donates a proton or an H+ ion when dissolved in water. For example HCl is an acid because it donates an H+ ion to H2O when it dissolves. The theory also states that a base is any substance that accepts a proton or an H+ ion. So in the same situation when HCl is dissolved in H2O the H2O acts as a base because it accepts an H+ ion and becomes H3O+ So in summary an acid can be any substance that donates an H+ ion or a proton and a base can be any substance that accepts the H+ ion or a proton.