Unit 11: Acids, Bases, and Salts

Unit 11: Acids, Bases, and Salts • RB Topic 8

I. Properties of Acids and Bases Acids Bases Electrolytes! high pH (7 – 14) Arrhenius definition: produce hydroxide ions as the only negative ion in solution (OH-) Ex: NaOH  Na++ OH- • Electrolyes! (conduct electricity in solution) • low pH (1 to 7) • Arrhenius definition: • produce hydrogen ions/hydronium ions as the only positive ion in solution (H+or H3O+) Ex: HCl + H2O  H3O+ + Cl- H2O

Acids Bases “Alternate definition” accept protons (H+) more OH- than H+ Table L Examples: Ex: NH3 + H2O  NH4+ + OH- • “Alternate definition” • donate protons (H+) • more H+ than OH- • Table K • Examples:

Acids Bases General formula: metalOH *NH3 is an exception • General formula: Hnonmetal(s) CxHyCOOH

Which of the following are bases? CH3COOH NH3 HCl HC2H3O2 Ca(OH)2 KCl NaF CH3CH2OH

II. The pH Scale • measures the H+ or H3O+ concentration in a solution • write concentration (molarity) as [H+]

“pH” stands for “potential to ATTRACT Hydrogen ions” • Acids have a LOW pH (release/DONATE H+) • Bases have a HIGH pH (grab up H+) • pH scale is logarithmic, which means that a change of ONE pH unit will change the concentration of H+ by a factor of TEN [H+] = 1 x 10-pH

strong acid weak acid weak base strong base neutral 0 7 14 [H+] = 1 x 100 M = 1 M [H+] = 1 x 10-7 M = 0.0000001 M [H+] = 1 x 10-14 M [H+] > [OH-] [H+] = [OH-] [H+] < [OH-]

Q: What is the relationship between pH value and hydrogen ion concentration?

III. Changes in pH

if pH changes by 1 unit, [H+] changes by a factor of 101 (10, “tenfold”) • if pH changes by 2 units, [H+] changes by a factor of 102 (100, “a hundredfold”) • if pH changes by 3 units, [H+] changes by a factor of 103 (1000, “a thousandfold”)

Ex: Describe what happens to the concentration of hydrogen ions in a solution if the pH is changed from 7 to 5

Ex: Describe what happens to the concentration of hydrogen ions in a solution if the pH is changed from 5 to 8

IV. How to measure pH • Use Table M! • If pH is below the first #, solution will be first color • If pH is above the second #, solution will be second color • If pH is between the #s, solution will be a mix of colors

V. Reactions of Acids with Metals • Use Table J! • acid + more active metal  H2(g) + a salt • *Cu, Au, and Ag (below H2 on Table J) do NOT react with acids

VI. Neutralization Reactions • acid + base  water + a salt • Ex: HCl (aq) + NaOH (aq)  H2O (l) + NaCl (aq) • *Write the products and balance the following: • ___ H2SO4 + ___ LiOH  • ___ HBr + ___ Ca(OH)2 

VII. Titrations • procedures used to determine the concentration (molarity) of an acid or a base

Titration setup

MAVA = MBVB If an acid and base are mixed…it’s a TITRATION!!! Use Reference Table T equation: MA = molarity of H+ VA = volume of acid MB = molarity of OH– VB = volume of base

Ex 1: A 16.0-milliliter sample of HNO3 (aq) is neutralized by 24.7 milliliters of 0.230 M KOH (aq). What is the concentration of the acid?

Ex 2: How many milliliters of 0.275 M NaOH are needed to neutralize 110. mL of 0.120 M HCl?

Unit 11: Acids, Bases, and Salts