Introduction to Acids and Bases 2/24/2019 Reference: Khady Guiro

DO NOW Brainstorm What are common acids and bases? What tools can be used to measure acids and bases?

Introduction Organisms are often very sensitive to the effect of acids and bases in their environment. They need to maintain a stable internal pH in order to survive—even in the event of environmental changes. Many naturally occurring biological, geological, and man-made chemicals are capable of stabilizing the environment’s pH. This may allow organisms to better survive in diverse environments found throughout the earth.

Introduction Cont. Acids and bases are a way of classifying compounds based upon what happens to them when you place them in water. An acid is a substance that yields an excess of hydrogen ions when dissolved in water. A base is a substance that yields an excess of hydroxide ions when dissolved in water.

Definitions of Acids and Bases An acid is a substance that breaks into ions in an aqueous solution. A Base (is a substance that breaks into ions in an aqueous solution. Note: aqueous solution is any solution where is the solvent.

ACIDS

Common Acids Vinegar (acetic or ethanoic acid) Citric Acid

Characteristics of Acids Sour taste (for edible acids) May burn your skin Turn litmus paper from blue to red.

Other Examples of Acids HCl Hydrochloric Acid H2SO4 Sulfuric Acid CH3COOH Acetic Acid (Vinegar)

BASES

Common Bases Ammonia

Characteristics of Bases Bitter taste (for edible bases only) Can be poisonous and corrosive. Feels slippery Turn litmus from red to blue.

Other examples of Bases Sodium Hydroxide NaOH Potassium Hydroxide KOH Ammonia NH3

Three Definitions of Acids and Bases

Three Definitions of Acids and Bases Svante Arrhenius (Swedish 1887) Bronsted- Lowry (Danish and English 1923 independently proposed definition) Gilbert Lewis (American 1920’s)

Arrhenius: based on Theory Ionization of Acids and Bases Acids produce hydrogen ions (H+) in an aqueous solution, while bases produce hydroxide ion (OH-). Acid: HCl (aq) H+ (aq) + Cl- (aq) Base: NaOH(aq) Na+(aq) + OH-(aq)

Bronsted- Lowry Definition of Acids and Bases An acid is a proton (H+) donor. A base is a proton (H+) acceptor. Example: HF + H2O H3O+ + F- Acid Base H3O+ : hydronium ion

Lewis Definition of Acids and Bases An acid accepts a pair of electrons. A base donates a pair of electrons. This is a more general definition than the previous two. Example: :NH3 + H+  NH4+

Three Models of Acids and Bases Definition of Acid Definition of Base Arrhenius H+ producer OH- producer Bronsted-Lowry H+ donor H+ acceptor Lewis Electron-pair acceptor Electron-pair donor

Binary acids Binary acids are certain molecular compounds in which hydrogen is combined with a second nonmetallic element; these acids include HF, HCl, HBr, and HI. HCl, HBr, and HI are all strong acids, whereas HF is a weak acid

Ternary acids 3 types of ternary compounds: Ternary salts Ternary acids (Oxyacids) Ternary bases

Conjugate Acids and Bases Conjugate acid is the particle formed that has received the proton. (ex: H3O+) Conjugate base is the particle left from the acid once it has donated the proton.

Conjugate Acids and Bases General expression: HA (aq) + H2O (l) H3O+ (aq) + A- (aq) Acid Base Conjugate Conjugate Acid Base

Conjugate Acid-Base Pairs conjugates acid base NH3 + H2O NH41+ + OH- base acid conjugates base acid CA CB NH3 + H2O NH41+ + OH-

Conjugate Acid-Base Pairs conjugates base2 acid2 HC2H3O2 + H2O H3O1+ + C2H3O2OH- acid1 base1 conjugates acid base CA CB HC2H3O2 + H2O H3O1+ + C2H3O2OH- The reaction proceeds in the direction such that the stronger acid donates its proton to the stronger base.