Acids and bases U N I T 9 Chapter 19

Introduction Unit 9: Acids and Bases

H2O(l) + H2O(l) ⇄ H3O+(aq) + OH–(aq) introduction The solvent in an aqueous solution is ________ Aqueous solutions contain hydrogen ions (H+)and hydroxide ions (OH–) In the self-ionization of water, the hydrogen ion exists as the hydronium ion H2O(l) + H2O(l) ⇄ H3O+(aq) + OH–(aq) The relative amounts or concentrations of H+/H3O+ and OH– determine whether solution is acidic, basic, or neutral [H+] = number of moles of H+ per liter of solution [OH–] = number of moles of OH– per liter of solution [ ] indicates molarity water

introduction High concentrations of hydrogen ions indicate acidic solutions [H+] > [OH–] pH < 7 High concentrations of hydroxide ions indicate basic solutions [H+] < [OH–] pH > 7 Equal concentrations of hydrogen and hydroxide ions indicate neutral solutions [H+] = [OH–] pH = 7 Pure water is the only substance with equal concentrations of these ions Other substances that form neutral solutions in water are classified as salts (chlorides, nitrates, sulfates, and carbonates)

Characteristics of acids and bases Unit 9: Acids and Bases

characteristics of Acids and Bases

characteristics of Acids and Bases corrosive

characteristics of Acids and Bases corrosive sour/tart taste bitter taste

characteristics of Acids and Bases corrosive sour/tart taste bitter taste turn litmus red turn litmus blue

characteristics of Acids and Bases corrosive sour/tart taste bitter taste turn litmus red turn litmus blue wet, not slippery, to touch soapy or slippery feel

characteristics of Acids and Bases corrosive sour/tart taste bitter taste turn litmus red turn litmus blue wet, not slippery, to touch soapy or slippery feel used in food and drink used in cleaning products

characteristics of Acids and Bases corrosive sour/tart taste bitter taste turn litmus red turn litmus blue wet, not slippery, to touch soapy or slippery feel used in food and drink used in cleaning products react with metals → H2 gas w/carbonates → CO2 gas, H2O, salt

Reaction with Metals

characteristics of Acids and Bases corrosive sour/tart taste bitter taste turn litmus red turn litmus blue wet, not slippery, to touch soapy or slippery feel used in food and drink used in cleaning products react with metals → H2 gas w/carbonates → CO2 gas, H2O, salt denature proteins (make food digestible) used in batteries, manufacturing

characteristics of Acids and Bases corrosive sour/tart taste bitter taste turn litmus red turn litmus blue wet, not slippery, to touch soapy or slippery feel used in food and drink used in cleaning products react with metals → H2 gas w/carbonates → CO2 gas, H2O, salt denature proteins (make food digestible) used in batteries, manufacturing conduct electricity in solution (electrolytes)

Electrolytes Electrolytes ionize when dissolved in solution Ions (charged particles) conduct an electric current Acids and bases produce ions, so they conduct electricity

Models of acids and bases Unit 9: Acids and Bases

Models of acids and bases The Arrhenius Model Acid Substance contains hydrogen and ionizes to produce hydrogen/ hydronium ion in solution HCl(g) → H+(aq) + Cl–(aq)

Models of acids and bases The Arrhenius Model Base Substance contains hydroxide group and dissociates to produce hydroxide ion in solution NaOH(s) → Na+(aq) + OH–(aq)

Models of acids and bases The Arrhenius Model Acids produce H+ ions Acidic solutions contain more H+ ions than OH– ions Bases produce OH – ions Basic solutions contain more OH–ions than H+ ions Problem: ammonia (NH3) is a base but does not produce hydroxide ions in solution

Models of acids and bases The Brønsted-Lowry Model More inclusive model: focuses on hydrogen ions, not hydroxide ions REVIEW An atom of hydrogen has _____ proton(s) and _____ electron(s). Hydrogen ______ its electron to become a __________ charged ion (_______) with a ______ charge. The hydrogen ion is, therefore, equivalent to a ________. one one loses positively cation 1+ proton

Models of acids and bases The Brønsted-Lowry Model ACID Hydrogen ion or proton donor Gives up H+ Produces conjugate base Conjugate base acts as a base in the reverse reaction

Models of acids and bases The Brønsted-Lowry Model BASE Hydrogen ion or proton acceptor Takes in H+ Produces conjugate acid Conjugate acid acts as an acid in the reverse reaction

Models of acids and bases Ionization of Hydrofluoric Acid A B CA CB HF(g) + H2O(l) ↔ H3O+(aq) + F-(aq) CA CB A B FORWARD REVERSE Acid and Base Conjugate Acid and Base Acid HF donates H+ and becomes F– CB F– acts as a base because it now accepts H+ Base H2O accepts H+ and becomes H3O+ CA H3O+ acts as an acid because it now donates H+

Models of acids and bases Dissociation of Ammonia A B CA CB H2O(l) + NH3(g) ↔ NH4+(aq) + OH-(aq) CA CB A B FORWARD REVERSE Acid and Base Conjugate Acid and Base Acid H2O donates H+ and becomes OH– CB OH– acts as a base because it now accepts H+ Base NH3 accepts H+ and becomes NH4+ CA NH4+ acts as an acid because it now donates H+

Models of acids and bases The Brønsted-Lowry Model Conjugate acid-base pair: two substances related to each other by donating and accepting a single H+ HF(g) + H2O(l) ↔ H3O+(aq) + F-(aq) A CB CA B Conjugate acid-base pairs: HF and F– differ by one hydrogen ion H2O and H3O+ differ by one hydrogen ion

Models of acids and bases The Brønsted-Lowry Model Conjugate acid-base pair: two substances related to each other by donating and accepting a single H+ H2O(l) + NH3(g) ↔ NH4+(aq) + OH-(aq) A CB CA B Conjugate acid-base pair: H2O and OH– differ by one hydrogen ion NH3 and NH4+ differ by one hydrogen ion

Models of acids and bases The Brønsted-Lowry Model B HF(g) + H2O(l) ↔ H3O+(aq) + F-(aq) A H2O(l) + NH3(g) ↔ NH4+(aq) + OH-(aq) When HF dissolves in water, water acts as a base When NH3 dissolves in water, water acts as an acid Amphoteric: a substance that can act as both an acid and as a base

Models of acids and bases The Brønsted-Lowry Model Identify the Brønsted-Lowry acid, base, conjugate acid, and conjugate base. HC2H3O2(aq) + H2O(l) ⇄ H3O+(aq) + C2H3O2-(aq) Acid ____________ Conjugate base ____________ Base ____________ Conjugate acid ____________ Conjugate acid-base pairs: HC2H3O2 C2H3O2- H2O H3O+ HC2H3O2 and C2H3O2- H2O and H3O+

nomenclature Unit 9: Acids and Bases

NOMENCLATURE Acids Binary Tertiary

NOMENCLATURE Binary Acids Hydro ________ ic acid Hydrofluoric acid Contain hydrogen and one other element Naming rule: prefix hydro–, root of second element, suffix –ic, and the word acid HF HCl Hydro ________ ic acid Hydrofluoric acid Hydrochloric acid

NOMENCLATURE Binary Acids Hydro ________ ic acid Hydrobromic acid HBr HI HCN is named as a binary acid Hydro ________ ic acid Hydrobromic acid Hydroiodic acid Hydrocyanic acid

Tertiary Acids or Oxyacids NOMENCLATURE Tertiary Acids or Oxyacids Contain hydrogen and oxyanions Oxyanions: polyatomic ions containing oxygen Naming rule: root of polyatomic ion, suffix, and the word acid

Tertiary Acids or Oxyacids NOMENCLATURE Tertiary Acids or Oxyacids Contain hydrogen and oxyanions Oxyanions: polyatomic ions containing oxygen Naming rule: root of polyatomic ion, suffix, and the word acid Polyatomic Ion Suffix Tertiary Acid Suffix

Tertiary Acids or Oxyacids NOMENCLATURE Tertiary Acids or Oxyacids Contain hydrogen and oxyanions Oxyanions: polyatomic ions containing oxygen Naming rule: root of polyatomic ion, suffix, and the word acid Polyatomic Ion Suffix Tertiary Acid Suffix –ate –ic

If you -ate something –icky, you’ll get the –ite–ous! NOMENCLATURE Tertiary Acids or Oxyacids Contain hydrogen and oxyanions Oxyanions: polyatomic ions containing oxygen Naming rule: root of polyatomic ion, suffix, and the word acid An easy way to remember: If you -ate something –icky, you’ll get the –ite–ous! Polyatomic Ion Suffix Tertiary Acid Suffix –ate –ic –ite –ous

NOMENCLATURE Tertiary Acids –ate → –ic acid –ite → –ous acid HNO3 HNO2 –ate → –ic acid –ite → –ous acid Nitric acid Nitrous acid

NOMENCLATURE Tertiary Acids –ate → –ic acid –ite → –ous acid H2SO4 H3PO3 –ate → –ic acid –ite → –ous acid Sulfuric acid Phosphorous acid

Monoprotic and Polyprotic Acids NOMENCLATURE Monoprotic and Polyprotic Acids Monoprotic: one hydrogen per molecule Examples: HNO3 HNO2 Polyprotic: more than one hydrogen per molecule H2SO4 is diprotic H3PO3 is triprotic

Ammonia (NH3) does not contain hydroxide NOMENCLATURE Bases A base is named with the element name of the cation and the name of the polyatomic anion (hydroxide) KOH Common name: potash lye NaOH Common name: soda lye Exception: Ammonia (NH3) does not contain hydroxide potassium hydroxide sodium hydroxide

strength of acids and bases Acids and bases are electrolytes, meaning that they produce ions in solution Therefore, solutions of acids and bases conduct electricity Strong acids ionize completely (100% ionization) in water, producing the maximum number of ions This property makes them good conductors of electricity Strong acids have a pH less than 3, and they form weak conjugate bases Weak acids produce fewer ions in solution because they only partially ionize (less than 100% ionization) in dilute aqueous solutions

strength of acids and bases Six Strong Acids All Others are Weak HCl HBr HI HClO4 HNO3 H2SO4 HF HCN HC2H3O2 H3PO4 H2CO3 HNO2 Ionization equations show how an acid or base produces ions in solution. For strong acids and bases an arrow in one direction (→) is used in the equation. For weak ones, an arrow in two directions (⇄) is used.

strength of acids and bases Strong bases dissociate entirely (100% dissociation) into metal ions and hydroxide ions in water The hydroxides of Group 1 and 2 metals are considered strong bases Strong acids have a pH greater than 10, and they form weak conjugate acids Weak bases only partially dissociate into ions (less than 100% dissociation) in dilute aqueous solutions

strength of acids and bases Strong Bases Common Weak Bases Hydroxides of Groups I and 2 metals NaOH KOH Ca(OH)2 NH3 C2H5NH2 CH3NH2

strength of acids and bases Strength and Conductivity Solutions that contain ions are able to conduct electricity and are called ______________ Acids and bases conduct an _________________ in solution The strength of the current is related to the __________ __________________________ Strong acids and bases will conduct a __________ electric current than weak acids and bases electrolytes electric current degree of ionization/dissociation stronger

strength of acids and bases Strength vs. Concentration In terms of concentration, Strong: Weak: When describing acids and bases, When referring to concentration of acids and bases, must use the terms Concentrated: Dilute: concentrated dilute 100% ionization/dissociation less than 100% ionization/dissociation high solute/low solvent low solute/high solvent

pH AND pOH The pH of a solution is related to the hydrogen ion concentration [H+] [H+] = moles of H+ per liter of solution The pOH of a solution is related to the hydroxide ion concentration [OH–] [OH–] = moles of OH– per liter of solution pH + pOH = 14.0

pH AND pOH The pH scale ranges in value from 0 to 14 A solution with a pH of 7 is considered neutral A pH of 0 is a strongly acidic solution A pH of 14 is a strongly basic solution One pH unit represents a ten-fold change in hydrogen ion concentration A solution with a pH of 2 has 10 times more H+ than a solution with a pH of 3

pH AND pOH pH 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 Strong Acids Strong Bases pOH 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0  Acidic Neutral Basic 

acid base indicators Acid base indicators change color in solution depending on the pH Litmus paper can identify a substance as acidic or basic but does not give pH value Changes color around pH of 7 Blue in bases and red in acids

acid base indicators Chemical indicators are organic molecules that work as dyes Phenolphthalein : colorless in acids and pink in bases Thymol blue: pink at pH 1; yellow at pH 4

acid base indicators When dipped in solution, pH paper changes to a wide range of colors, which is compared to a key to determine pH A pH meter is an electronic device that gives pH on LCD readout

acid base indicators Certain natural substances, such as beet juice and purple cabbage juice, also change color in solutions of different pH

buffers A buffer is a solution that resists changes in pH when acids or bases are added in small amounts Purpose: to maintain the pH of a solution within a specific range Applications: Aquariums and pools Digestive system Blood

buffers The pH of human blood is about 7.4, making it slightly basic. The bicarbonate ion (HCO3–) is present in the blood as a buffer, helping maintain homeostasis When too many H+ are present, HCO3– functions as a base by accepting H+ and forming H2CO3 HCO3 – + H2O ⇄ H2CO3 + OH – Fewer H+, less acidic, pH ↑

buffers If there are not enough H+ in the blood, HCO3– functions as an acid by donating H+ to solution and forms carbonate ion (CO32–) HCO3 – + H2O ⇄ CO32– + H3O+ More H+, more acidic, pH ↓

neutralization Neutralization reaction: type of double replacement reaction in which an acid and a base react in aqueous solution to produce water and a salt (ionic compound composed of a cation from a base and an anion from an acid) Acid + Base → H2O + Salt

neutralization Last December, a 1-square-mile area of Sapulpa, Oklahoma was closed due to a hydrochloric acid spill from a tractor-trailer. People in the area had to leave their homes because of the threat of toxic fumes. How is such an acid spill handled? In the case of a strong acid, such as hydrochloric acid, a weak base is added to “neutralize” the acid A strong base could neutralize the acid spill but would generate a tremendous amount of heat (exothermic reaction)

Acids and bases U N I T 9 Chapter 19