Chapter 14 – Acids, Bases, and pH Section 1 –Acids and Bases

Properties of Acids 1) Aqueous solutions of acids have a sour taste 2) Acids change the color of acid-base indicators 3) Some acids react with active metals and release H2 Ba(s) + H2SO4(aq) -> BaSO4(s) + H2(g)

Properties of Acids 4) Acids react with bases to produce salts and water A “salt” is any ionic compound formed from an acid reacting, not just NaCl

5) Acids conduct electric current Think “battery acid” 6) React w/ CO32- to form CO2, H2O, and another compound -2HCl + K2CO3  CO2 + H2O + 2KCl

Properties of Bases Aqueous solutions of bases taste bitter 2) bases change the color of acid-base indicators 3) dilute aqueous solutions of bases feel slippery

4) bases react with acids to produce salts and water 5) bases conduct electric current

Indicators Indicators are dyes that change color when exposed to an acid or a base Lots of different substances can be indicators phenolphthalein, red cabbage Litmus is the most common indicator Acids turn it red; bases turn it blue

Defining Acids An acid is a substance that produces hydronium ions when it dissolves in water

A hydronium ion (H3O+) consists of a hydrogen ion attached to a water molecule HCl + H2O  H3O+ + Cl- HC2H3O2 + H2O  H3O+ + C2H3O2-

Acidic Hydrogen Atoms Hydronium ions are formed when a hydrogen ion (H+) transfers from an acid to water (H+ + H2O  H3O+)

Any hydrogen atom in an acid that can be transferred to water is called an acidic hydrogen HCl + H2O  H3O+ + Cl- HC2H3O2 + H2O  H3O+ + C2H3O2-

Acidic Hydrogen Atoms To help distinguish acids from other hydrogen-containing molecules acidic hydrogens are written first in the formula HCl H2SO4

The number of acidic hydrogens an acid has is different depending on the acid

Monoprotic Acids An acid that can donate only one proton per molecule is a monoprotic acid HCl + H2O -> H3O+ + Cl-

After the HCl donates one proton there are no others for it to donate

Polyprotic Acids An acid that can donate more than one proton per molecule is a polyprotic acid

Polyprotic Acids An acid that can donate two protons per molecule is a diprotic acid H2SO4 + H2O -> H3O+ + HSO4- HSO4- + H2O <-> H3O+ + SO42- After the H2SO4 donates one proton there is still another for it to donate

Polyprotic Acids An acid that can donate three protons per molecule is a triprotic acid H3PO4 + H2O <-> H3O+ + H2PO4- H2PO4- + H2O <-> H3O+ + HPO42- HPO42- + H2O <-> H3O+ + PO43- After the H3PO4 donates one proton there are still two more for it to donate

Acid Ionization The process of ions forming from a ionic compound is called ionization Since acids are ionic compounds, the formation of ions from acids is called acid ionization

The ability to ionize in water is what gives acids the ability to conduct electricity

Common Industrial Acids Sulfuric Acid Most commonly produced industrial chemical in the world Nitric Acid Phosphoric Acid

Hydrochloric Acid Acetic Acid Concentrated solutions of HCl are referred to as muriatic acid Acetic Acid Pure acetic acid is a clear, colorless, pungent-smelling liquid known as glacial acetic acid

Defining Bases A base is a substance that produces hydroxide ions (OH-) when it dissolves in water There are two ways this can happen: metal hydroxides and some covalent compounds

Metal Hydroxides Metal hydroxides are ionic compounds made of a metal cation and OH- NaOH  Na+ + OH- Unlike acids, water doesn’t react with the base – it is simply present when the dissociation occurs. There is no transfer of ions between water and the base. Acids can have multiple acidic hydrogens; bases can have multiple hydroxide ions Ca(OH)2, Al(OH)3

Ionic Compounds as Bases A few bases are ionic compounds that produce OH- when they ionize in H2O The ionization involves the transfer of a H+ from water to the base NH3 + H2O  NH4+ + OH- B + H2O  BH+ + OH- Both produce OH- so both are bases

Bases are Electrolytes Like acids, bases produce ions in water This makes them good conductors of electricity

Anhydrides Anhydrides are compounds containing oxygen bonded to just one other element; the word anhydride means that they do not contain water Although they do not fit our previous definitions of acids and bases they still act as acids and bases

Anhydrides Nonmetal oxides react with water to form acids and are called acidic anhydrides Metal oxides react with water to form bases and are called basic anhydrides

Acidic Anhydrides and Acid Rain CO2 exists naturally in the atmosphere; it reacts with H2O to form carbonic acid CO2 + H2O  H2CO3 This makes all rain slightly acidic

Other chemicals are released as pollutants into the atmosphere from cars, power plants, etc. (SO2, SO3, NO, NO2); they also react with water to form acids Very acidic rain is called acid rain

Basic Anhydrides and Growth Lime (CaO) is often added to soil to make it less acidic, which is favorable to plant growth CaO + H2O  Ca(OH)2 Metal oxides like Na2O, K2O, and CaO are also used to make soap; they also react with water to form bases Most soaps/cleaners are bases because what we need to clean is acidic