Acids, Bases, and Salts Chapter 19

Chapter 19: Terms to Know Monoprotic acid Diprotic acid Triprotic acid Conjugate acid Conjugate base Conjugate acid-base pair Amphoteric Lewis acid Lewis base Hydronium ion Self-ionization Neutral solution Ion-product constant for water Acidic solution Basic solution Alkaline solution pH

Introduction Acids and bases are commonly used inside and outside of the chemistry lab and have distinctive properties. There are three main theories that explain acid/base properties. Water can self-ionize to for hydrogen ions and hydroxide ions. The pH scale is a way to measure the acidity or basicity of a solution.

I.) Naming Acids Treat acids as if they were anions combined with enough hydrogen ions to make a neutral compound. Acids will have the basic formula HnX, where “n” is the number of hydrogens and “X” is a monatomic or polyatomic ion. Three rules for dealing with the naming of acids.

Naming acids Acids are ionic compounds where hydrogen is the cation. These are the oxygen containing acids, or oxo acids. These are the binary acids

Rule #1: Compounds That End in -ide Acid name begins with prefix hydro- Drop –ide and add –ic Add the word “acid” at the end These compounds are often binary molecular compounds that do not have oxygen as a component.

Give the name of the following acid: HCl. Is this a binary compound? What is the prefix? What is the anion? Name of anion: How does the suffix of the anion change? What is the complete name of the acid? Answer: hydrochloric acid

Give the name of the following acid: H2S. Is this a binary compound? What is the prefix? What is the anion? Name of anion: How does the suffix of the anion change? What is the complete name of the acid? Answer: K2SO4

Rule #2: Compounds That End in –ite Drop –ite and add –ous. Add the word “acid” at the end. The anions of these compounds have oxygen as a component. All of these are polyatomic acids. Do not use the prefix “hydro-”.

Give the name of the following acid: H2SO3. Is this a binary compound? What is the prefix? What is the anion? Name of anion: How does the suffix of the anion change? What is the complete name of the acid? Answer: sulfurous acid

Give the name of the following acid: H3PO3. Is this a binary compound? What is the prefix? What is the anion? Name of anion: How does the suffix of the anion change? What is the complete name of the acid? Answer: phosphorous acid

Rule #3: Compounds That End in –ate Drop –ate and add –ic. Add the word “acid” at the end. Again these acids are derived from compounds that have polyatomic anions with oxygen as a component. Do not use the prefix “hydro-”.

Give the name of the following acid: H3PO4. Is this a binary compound? What is the prefix? What is the anion? Name of anion: How does the suffix of the anion change? What is the complete name of the acid? Answer: phosphoric acid

Give the name of the following acid: H2SO4. Is this a binary compound? What is the prefix? What is the anion? Name of anion: How does the suffix of the anion change? What is the complete name of the acid? Answer: sulfuric acid

II.) Writing Formulas from Acid Names Simply use the reverse process to obtain the formulas from the names of the acids. Make sure that you include enough hydrogen ions (H+) to balance the charges of the anions.

Give the formula for the following compound: hydrochloric acid. Is this a binary compound? How do you know? Symbol for cation: What is the anion? Symbol for anion: Does one cation and one anion balance each other out? If not, how many of each are needed to balance the charges? Answer: HCl

Give the formula for the following compound: nitric acid. Is this a binary compound? How do you know? Symbol for cation: What is the anion? Symbol for anion: Does one cation and one anion balance each other out? If not, how many of each are needed to balance the charges? Answer: HCl

III.) Names and Formulas for Bases Bases are named in the same way as other ionic compounds – the name of the cation followed by the name of the anion. The key to identifying bases is to look for the OH- ion.

Give the formula for the following compound: potassium hydroxide. Is this a binary compound? What is the cation? Symbol for cation: What is the anion? Symbol for anion: Does one cation and one anion balance each other out? If not, how many of each are needed to balance the charges? Answer: KOH

Give the formula for the following compound: Iron(III) hydroxide. Is this a binary compound? What is the cation? Symbol for cation: What is the anion? Symbol for anion: Does one cation and one anion balance each other out? If not, how many of each are needed to balance the charges? Answer: Fe(OH)3

Acid-Base Theories (Section 19.1) Properties of Acids and Bases Arrhenius Acids and Bases Bronsted-Lowry Acids and Bases Lewis Acids and Bases

I.) Properties of Acids and Bases Acids have properties that are more familiar to us. The properties of bases are less familiar. Both acids and bases are electrolytes.

Properties of acids. Acids have a sour taste. Acids changes the colors of an acid-base indicator. Acids can be strong or weak electrolytes.

Properties of bases. Most bases taste bitter. Bases have a slippery feel. Bases will also change the color of an acid-base indicator. Bases can also be strong or weak electrolytes.

II.) Arrhenius Acids and Bases Acids are hydrogen containing compounds that ionize to yield hydrogen ions in aqueous solutions. Bases are compounds that ionize to yield hydroxide ions in aqueous solutions Svante Arrhenius 1859 - 1927

Arrhenius Acids Acids are compounds that can yield H+ ions in aqueous solutions. Monoprotic acids: Acids with 1 ionizable H+ Diprotic acids: Acids with 2 ionizable H+ Triprotic Acids: Acids with 3 ionizable H+ Not all compounds with hydrogen atoms are acids. Hydrogen atoms must be attached to an electronegative atom.

Sample problem #1 Identify each acid as monoprotic, diprotic, or triprotic. H2CO3 H3PO4 HCl H2SO4

Arrhenius bases. Bases are compounds that can yield an OH- ion in aqueous solution. Bases of the Group 1A metals are very strong bases and dissociates completely in aqueous solution. Bases of other metals do not dissociate completely.

Examples of Arrhenius acids and bases. HCl KOH HNO3 NaOH H2SO4 Ca(OH)2 H3PO4 Mg(OH)2

III.) Bronsted-Lowry Acids and Bases This theory is broader than the Arrhenius theory. Acids are H+ ion donors Bases are H+ ion acceptors. Johannes Bronsted (1879 – 1947)

Conjugate acids and bases Conjugate acid: A particle formed when a base gains a H+ ion. Conjugate base: The particle that remains after an acid has donated its H+ ion. NH3(aq) + H2O(l) → NH4+(aq) + OH-(aq) Base Acid Conjugate Acid Conjugate Base

Conjugate Acid-Base Pairs HCl Cl- H2SO4 HSO4- H3O+ H2O SO42- CH3COOH CH3COO- OH- Water is an amphoteric compound because it can be both an acid and a base.

IV.) Lewis Acids and Bases This theory is the broadest. Acid = electron pair acceptor Base = electron pair donor Gilbert Lewis (1875 – 1946)

Examples of Lewis acid and bases. H+ OH- H2O BF3 NH3 AlCl3 Cl-

Comparing all three acid/base theories. Theory Acid Base Arrhenius H+ producer OH- producer Bronsted-Lowry H+ donor H+ acceptor Lewis Electron-pair acceptor Electron-pair donor

Hydrogen Ions and Acidity (Section 19.2) Hydrogen Ions from Water Ion Product Constant for Water The pH Concept Measuring pH

I.) Hydrogen Ions from Water Water molecules are highly polar. Collisions of two water molecules results in the transfer of a H+ This process occurs to a small extent. The Hydronium Ion

II.) Ion Product Constant for Water Kw = [H+] x [OH-] = 1.0 x 10-14 The H+ and OH- concentration of pure water is 1x10-7 M. This is a neutral solution. The product of the two concentrations is 1x10-14 M for dilute aqueous solutions. Adding acids or bases to a neutral solution will change the ion product constant for water.

Using ion-product constant to solve for H+ and OH- concentrations. If [H+] is less than 1.0 x 10-7 M, the solution is basic. If [H+] is greater than 1.0 x 10-7 M, the solution is acidic. If we know the ion concentration of either H+ or OH- for a solution we can solve for the other using the ion-product constant.

Sample problem Colas are slightly acidic. If the [H+] in a solution is 1.0 x 10-5 M, is the solution acidic, basic or neutral? What is the [OH-] of this solution?

III.) The pH Concept The pH scale is a less cumbersome way of expressing the [H+]. The scale ranges from 0 – 14. pH 7 = neutral, pH 0 = very acidic, pH 14 = very basic.

pH = -log[H+] Calculating pH. Calculating the pH of a solution is a very simple process. The pH of a solution is the negative logarithm of the [H+]. Calculate pH by using the log key on your calculator and using the above formula.

Sample problem What is the pH of a solution with a [H+] of 4.2x10-10M?

pOH = -log[OH-] pH + pOH = 14 Calculating pOH. There is one of two ways that you can solve for the pOH: pOH = -log[OH-] pH + pOH = 14

IV.) Measuring pH There are many reasons why we need to know the pH of a solution in the real world and the lab. There are chemical indicators and instruments to do this.

Acids, Bases, And Salts Chapter 19 The End