Acid & Base Solutions. Properties of Acids What we know about acids: Sour taste pH 0 – 7 Turns blue litmus to red Turns methyl orange to red.

Acid & Base Solutions

Properties of Acids What we know about acids:

Sour taste pH 0 – 7 Turns blue litmus to red Turns methyl orange to red

Indicator: a chemical compound that changes color in the presence of H+ ions

Ionic chemical formula starts with “H” Are electrolytes

Electrolytes – substances that conduct electricity while dissolved in water

Physical Properties of AcidsAcids will react with:… some metals to produce a salt and H2 gas

• Mg + 2HCl → MgCl2 + H2

… metal oxides to produce a salt and H2O.• Li2O + 2HCl → 2LiCl + H2O

… metal carbonates to produce a salt, H2O, and CO2.

• Na2CO3 + 2HCl → 2NaCl + H2O + CO2

… bases to produce a salt and H2O.• Ca(OH)2 + 2HCl → CaCl2 + 2H2O

Naming Acidso Common strong acids:

o HCl - hydrochloric acido HBr - hydrobromic acido HNO3 - nitric acido HClO3 - chloric acido H2SO4 - sulfuric acid

o Common weak acidso HC2H3O2 - Acetic acido HF - Hydrofluoric acid*Note: These all start with H and are ionic!

Properties of Bases

Coffee is acidic, but caffeine is alkaline (basic), and contributes to the bitter taste

What we know about bases: bitter taste Slippery to touch

Fats on skin get turned into soap pH 7 – 14 Turns red litmus to blue Turns phenolphthalein to pink Ionic chemical formula ends with “OH” Are also electrolytes Reacts with acids to produce a salt & water

• HCl + NaOH NaCl + H2O

Naming Baseso Like strong acids, strong bases

ionize completely.o Strong bases = soluble hydroxides

o LiOH - lithium hydroxideo NaOH - sodium hydroxideo KOH - potassium hydroxideo Ca(OH)2 - calcium hydroxideo Sr(OH)2 - strontium hydroxideo Ba(OH)2 - barium hydroxide

o Weak Baseso NH3 - ammoniao Insoluble bases

Acid & Base Definition There are 3 common definitions of acids and bases.

Arrhenius definition – acids increase H+ concentration, bases increase OH- concentration

Brønsted-Lowry definition – acids are proton donors, bases proton acceptors

Lewis definition – acids accept a pair of electrons Arrhenius acid- a substance that produces an H+ (or H

3O+)

cation in solution. Acids dissociate like salts because of water’s strong polarity

HCl(aq) → Cl-(aq) + H+(aq) can also be written as: HCl(aq) + H2O(l) → Cl-(aq) + H3O+(aq) H3O+ is called hydronium

Acid & Base Definition

+

+

Hydrochloric acid dissociates because it is ionic

+

Acid & Base Definition

+

Arrhenius Base- a substance that produces an OH- anion in solution. NaOH(s) → Na+(aq) + OH-(aq)

Neutralization Reaction

+ +

ReviewpH Scale

Traditionally 0 - 14.Can have pH < 0 or > 14.

pH < 7 Acidic solution.pH > 7 Basic solution.pH = 7 Neutral solution.

pH Scale

Acidic Basic

0 1 2 3 4 5 6 7 8 9 10

11

12

13

14

The pH Concept Water is extremely polar

Auto-ionizes by itself H2O(l) ↔ H+(aq) + OH-(aq)

1mol 1mol 1mol Double-arrow means reaction goes in both directions Called “self-ionization”

In solution, the H+ and OH- concentrations are equal. A solution where [H+] = [OH-] is called neutral

Not all solutions are neutral Solutions with acids increase the concentration of H+

Called acidic

Solutions with bases increase the concentration of OH-

Called basic

pH Concept pH system developed by Danish chemist Søren

Sørensen pH = - log [H+] (page 3 NC Chemistry Ref. Tables)

“the power of the Hydrogen ion” Based on the concentration of hydrogen ions in

solution [H+] = the concentration of the H+ ion in solution

Monoprotic acids (“one proton”)-concentration of the acid is equal to the concentration of the H+ produced Ex: HCl → H+ + Cl- one mole of HCl produces one mole of hydrogen ions

and one mole of chloride ions Diprotic acids produces twice as many H+ ions

Ex: H2SO4 → 2H+ + SO42-

pH Concept pH and concentration formula

pH = -log [H+] [H+] = Molar concentration of H+ ion Example: What is the pH of a 0.0045 M HCl

solution? Note: the concentration of H+ is the same as

HCl, because there is only one H+ is produced

pH = - log [0.0045M] pH = 2.35

** double check- is this pH good for an acid? What is the pH of a solution with a concentration

of acetic acid(HC2H3O2) at 3.98x10-6M? pH = - log [3.98x10-6] pH = 5.40

pH and pOH pOH is the “power of hydroxide”

Formula: pOH = - log [OH-] Example: What is the pOH of a 3.41 x 10-4

M NaOH solution? pOH = -log[OH-]

= -log[3.41 x 10-4 M] = 3.47

pH and pOH Bases have pH values too

Earlier, we stated that in pure water, [H+] and [OH-] are equal. Therefore:

pH + pOH = 14 (Page 3 of NC Ref. Tables) What is the pH of the base in the previous

example? pH + pOH = 14 pH + 3.47 = 14 pH = 10.53

** is this a good pH for a base?