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 (NH3)

Lewis concept of Acids and Bases: Lewis Acid Substance that can accept a pair of electrons to form a covalent bond Lewis Base 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 H+ donor H+ acceptor Lewis Electron-pair acceptor Electron-pair donor

Strengths of Acids and Bases: Strong acids – completely ionised in aqueous solution Ex: HCl; HNO3; H2SO4 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; NaOH; KOH Weak bases – react with water to form hydroxide ion and the conjugate acid of the base (No OH in formula) Ex: CH3NH2, NH3

Single Element: Polyatomic Ion: Hydro_____ic acid Ex: HCl = Hydrochloric acid Polyatomic Ion: ATEic ITEous Ex: H2SO4 = sulfuric acid Ex: H2SO3 = 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 (H3O+)

Self-ionisation of water: reaction in which TWO water molecules produce ions Ex: H2O + H2O  H3O+ + OH- Can also be written as a DISSOCIATION: Ex: H2O (l)  H+ (aq) + OH- (aq)

In water or aqueous solution, hydrogen ions (H+) are joined to water molecules to form hydronium ions (H3O+) H+ and H3O+ 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 pH pH = -log[H+] Acidic: pH < 7; [H+] > 1 x 10-7 M Basic: pH > 7; [H+] < 1 x 10-7 M Neutral: pH = 7; [H+] = 1 x 10-7 M

Basicity could be measured in a similar manner called pOH pOH = -log[OH-] pH + pOH = 14

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

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