Acids and Bases Mr Sonaji V Gayakwad Asst

Acids and Bases Mr. Sonaji V. Gayakwad Asst. professor Dept of chemistry Mrs. K. S. K. College, Beed

Arrhenius theory of Acid and Bases Arrhenius Acids ◦ Hydrogen-containing compounds that ionize to yield hydrogen ions (H+) in aqueous solutions Arrhenius Bases ◦ Compounds that ionize to yield hydroxide ions (OH) in aqueous solutions

Bronsted-Lowry theory of Acids and bases Bronsted-Lowry Acid ◦ A hydrogen-ion donor Bronsted-Lowry Base ◦ A hydrogen-ion acceptor

All acids and bases in the Arrhenius theory are also acids and bases based on Bronsted. Lowry theory. Bronsted-Lowry includes some bases not included in the Arrhenius theory. ◦ Ex: Ammonia (NH 3)

Lewis concept of Acids and Bases: Lewis Acid Lewis Base ◦ Substance that can accept a pair of electrons to form a covalent bond ◦ Substance that can donate a pair of electrons to form a covalent bond

What are acids and bases? Summary of Acid-Base Definitions Theory Acid Base Arrhenius H+ producer OH- producer Bronsted. Lowry Lewis H+ donor H+ acceptor Electron-pair donor

Strengths of Acids and Bases: Strong acids – completely ionised in aqueous solution ◦ Ex: HCl; HNO 3; H 2 SO 4 Weak acids – ionise only slightly in aqueous solution ◦ Ex: Acetic acid – 1% of acetic acid molecules ionised at any instant

Strong bases – dissociate completely into metal ions and hydroxide ions in aqueous solution ◦ Ex: Ca(OH)2; Na. OH; KOH Weak bases – react with water to form hydroxide ion and the conjugate acid of the base (No OH in formula) ◦ Ex: CH 3 NH 2, NH 3

Single Element: ◦ Hydro_____ic acid ◦ Ex: HCl = Hydrochloric acid Polyatomic Ion: ◦ ATEic ITEous ◦ Ex: H 2 SO 4 = sulfuric acid ◦ Ex: H 2 SO 3 = sulfurous acid

Bases are named the same way as any other ionic compound Ex: KOH = potassium hydroxide

Water that LOSES a hydrogen ion becomes a negatively charged hydroxide ion (OH-) Water that GAINS a hydrogen ion becomes a positively charged hydronium ion (H 3 O+)

Self-ionisation of water: reaction in which TWO water molecules produce ions Ex: H 2 O + H 2 O H 3 O+ + OHCan also be written as a DISSOCIATION: Ex: H 2 O (l) H+ (aq) + OH- (aq)

In water or aqueous solution, hydrogen ions (H+) are joined to water molecules to form hydronium ions (H 3 O+) H+ and H 3 O+ are both used to represent hydrogen ions in aqueous solution

Acidity or basicity of a solution is discussed in terms of the concentration of hydrogen ions, [H+], or the concentration of hydroxide ions, [OH-] Acidic: [H+] > [OH-] Basic (Alkaline): [H+] < [OH-] Neutral: [H+] = [OH-]

Acidity is measured in p. H = -log[H+] Acidic: p. H < 7; [H+] > 1 x 10 -7 M Basic: p. H > 7; [H+] < 1 x 10 -7 M Neutral: p. H = 7; [H+] = 1 x 10 -7 M

Basicity could be measured in a similar manner called p. OH = -log[OH-] p. H + p. OH = 14

Acid-Base Indicators ◦ An indicator’s acid and base form have different colors in solution ◦ Limitations: usually work at 25°C p. H Meters ◦ Ex: PASCO Probes ◦ Make rapid, accurate p. H measurements ◦ Must be calibrated – put into solution of known p. H

Neutralisation reaction: hydronium ions combine with hydroxide ions to form water An indicator can be used to show when the neutralisation is complete