Dressen-Intro to Acids-Bases-pH

Acids and Bases:

1 Acids and Bases

Properties of Acids:

2 Properties of Acids Produce H + (as H 3 O + ) ions in water (the hydronium ion is a hydrogen ion attached to a water molecule) Taste sour Corrode metals Good Electrolytes React with bases to form a salt and water pH is less than 7 Turns blue litmus paper to red “Blue to Red A-CID”

Properties of Bases:

3 Properties of Bases Generally produce OH - ions in water Taste bitter, chalky Are electrolytes Feel soapy, slippery React with acids to form salts and water pH greater than 7 Turns red litmus paper to blue “ B asic B lue ”

Naming Acids:

4 Naming Acids Binary Acid – An acid that contains only two elements, one of which is hydrogen and one which is more electronegative. HF – Hydro fluor ic acid HCl – Hydro chlor ic acid Oxyacid – An acid that has hydrogen, oxygen, and a third element that is usually a non-metal HClO 4 – Perchlor ic acid HNO 2 – Nitr ous acid H2CO 3 – Carbon ic acid

Arrhenius Definition:

5 Arrhenius Definition Acid - Substances in water that increase the concentration of hydrogen ions ( H + ). Base - Substances in water that increase concentration of hydroxide ions ( OH - ). Problem – many bases do not actually contain hydroxides

Bronsted-Lowry Definition:

6 Bronsted-Lowry Definition Acid - neutral molecule, anion, or cation that donates a proton. Base - neutral molecule, anion, or cation that accepts a proton. HA + :B  HB + + :A - HCl + H 2 O  H 3 O + + Cl - Acid Base Conj Acid Conj Base

Conjugate Acid Base Pairs:

7 Conjugate Base - The species remaining after an acid has transferred its proton. Conjugate Acid - The species produced after base has accepted a proton. HA & :A - - conjugate acid/base pair :A - - conjugate base of acid HA :B & HB + - conjugate acid/base pair HB + - conjugate acid of base :B Conjugate Acid Base Pairs

Examples of Bronsted-Lowry Acid Base Systems:

8 Note: Water can act as acid or base Acid Base Conjugate Acid Conjugate Base HCl + H 2 O  H 3 O + + Cl - H 2 PO 4 - + H 2 O   H 3 O + + HPO 4 2- NH 4 + + H 2 O   H 3 O + + NH 3 Base Acid Conjugate Acid Conjugate Base :NH 3 + H 2 O   NH 4 + + OH - PO 4 3- + H 2 O   HPO 4 2- + OH - Examples of Bronsted-Lowry Acid Base Systems

Diprotic and Triprotic Acids (Polyprotic):

9 Diprotic and Triprotic Acids (Polyprotic) Sulfuric Acid can donate two protons per molecule Phosphoric acid can donate three protons per molecule H 3 PO 4 + H 2 O   H 3 O + + H 2 PO 4 - H 2 PO 4 - +H 2 O   H 3 O + + HPO 4 2- HPO 4 2- +H 2 O   H 3 O + + PO 4 3-

G.N. Lewis Definition:

10 Lewis Acid - an electron pair acceptor Base - an electron pair donor G.N. Lewis Definition

Common Strong Acids/Bases:

11 Common Strong Acids/Bases Strong Bases Sodium Hydroxide Potassium Hydroxide *Barium Hydroxide *Calcium Hydroxide *While strong bases they are not very soluble Strong Acids Hydrochloric Acid Nitric Acid Sulfuric Acid Perchloric Acid

Acid Strength:

12 Acid Strength Strong Acid Weak Acid Transfers all of its protons to water Transfers only a small fraction of its protons to water Completely Ionized Partly Ionized Strong Electrolyte Weak Electrolyte Conjugate Base is Weaker Conjugate Base is Stronger As acid strength decreases, base strength increases The stronger the acid, the weaker its conjugate base The weaker the acid, the stronger its conjugate base

Base Strength:

13 Base Strength Strong Base Weak Base All molecules accept a proton Fraction of molecules accept a proton Completely Ionized Partly Ionized Strong Electrolyte Weak Electrolyte Conjugate Acid is Weaker Conjugate Acid is Stronger As base strength decreases, acid strength increases The stronger the base, the weaker its conjugate acid The weaker the base, the stronger its conjugate acid

Salts & Neutralization:

14 Salts & Neutralization A salt is the neutralization product of an acid and a base. The anion comes from the acid and the cation from the base. Examples H Cl + Na OH  Na Cl + H 2 O . H 2 SO 4 + 2 K OH  K 2 SO 4 + H 2 O.

The pH Scale:

15 The pH Scale pH [H 3 O + ] [OH- ] pOH

pH and acidity:

16 pH and acidity Acidity or Acid Strength depends on Hydronium Ion Concentration [H 3 O + ] The pH system is a logarithmic representation of the Hydrogen Ion concentration (or OH - ) as a means of avoiding using large numbers and powers. pH = - log [H 3 O + ] pOH = - log [OH - ] 3. What is the pH of a solution if the [H 3 O + ] is 3.4 x 10 -5 M? pH = -log [H 3 O + ] = -log(3.4 x 10 -5 ) = 4.47

pH and acidity:

17 pH and acidity Kw = [H 3 O + ] [OH - ] = 1.0 x10 -14 In pure water [H 3 O + ] = [OH - ] = 1.0 x10 -7 pH + pOH = 14

Indicators:

18 Indicators

pH and acidity:

19 pH and acidity The pH values of several common substances are shown at the right. Many common foods are weak acids Some medicines and many household cleaners are bases.