Unit 8: Acids and Bases

Correlates to Topic 10 in review book, pages 174-188

Unit 8: Acids and Bases

Acids = substances that react with a base; often has a low pH

May be strong or weak

Actual definition depends upon the type of acid/base

Bases = substances reacting with an acid; often has a high pH

May be strong or weak

3 major types of acids and bases here

Characteristics of Acids and Bases

Acids:o Taste souro Conduct current in

solutiono React with bases

to form water and salt

o React with some metals to make H2(g)

o Low pH

Bases:o Taste bittero Slippery/soapy

feelingo Conduct current in

solutiono React with acids

to form salt watero Have low pOH or

high pH

II. Types of Acids and Bases

1. Arrhenius 2. Bronsted-Lowry

1. Arrhenius Acid/Base

Acid = substances that release hydrogen ions in aqueous solutions

proton donors

Ex.] HCl H+ + Cl-

Base = substances that release hydroxide ions in aqueous solutions

Hydroxide donors

Ex.] NaOH Na+ = OH-

2. Bronsted-Lowry Acid/Base

Acid = any substance that can donate hydrogen ions in solutiono Proton donors

Ex.] HCl H+ + Cl-

Base = any substance that can accept hydrogen ions in solution

Proton acceptors

Ex.]NH3 + H+ NH4+

Lewis Acids and Bases [non-Regents]

Acid = any species that can accept an electron pair from another species in solution

Ex.] H+ + NH3

Base = any species that can donate an electron pair to another species in solution

NH4+

III. Strengths of Acids and Bases

STRONG acids/bases will completely dissociate [ionize] in solution

Ex.] HCl, HNO3, H2SO4, NaOH, KOH, etc.

WEAK acids/bases produce very few ions per molecule in solution

Ex.] vinegar, H3PO4, formic acid, citric acid, etc.

Acid and Base Conjugates

Acid/Base Conjugates = species that are formed in solution as a result of the dissociation of an acid or base

Ex.] HCl + NaOH Na+ + Cl- + HOH

o Cl- is the conjugate baseo Na+ is the conjugate acid

IV. Titrations

Titration = method used to determine the pH of an unknown solution

Process to find the concentration of an unknown acid/base by neutralizing it with a base/acid of known concentration

An indicator signals the equivalence point and tells that the neutralization is complete

Titrations, [continued]

Uses burets, a standard solution of known pH, an indicator, and a fixed volume of a solution with an unknown pH

Titration Formula:

MaVa = MbVb

http://www.youtube.com/watch?v=u9nOIZDdvRw

Acid-Base Reactions

Acid + Base = Salt + water

Acids and bases neutralize each other

H+ + OH- H2O

V. pH and pOH

pH = the scale, 0-14, that defines the acidity or basicity of a solution

Based on the concentration of hydrogen ions

• 0-6 = acid• 7= neutral• 8-14 = base

pOH pOH = the

measure of the concentration of OH- ions in solution

Opposite of pH

Scale 0-14• 0-6 = strong base• 7= neutral• 8-14 = acidic

Relating pH and pOH

pH + pOH = 14 always!

pH = -log[H+]

pOH = -log[OH-]

B. pH and pOH Calculations

Ex. 1] What is the pH of a solution containing 9.15 x 10-6 M H+?

Ex. 2] What is the pH of a solution containing [OH-] = 8.11 x 10-5 M in 350.mL of solution?

C. Indicators Indicators = compounds that

change color when the pH changes

oColor changes indicate the pH of the solution!

oUse several indicators to pinpoint the final pH!

Indicators: Table M

Find the pH using the indicator and its color in the solution…

Tutorial on indicators:

http://www.kentchemistry.com/links/AcidsBases/Indicators.htm

Expanded Indicators Chart