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Acids and Bases

Acids and Bases. What are acids 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. What are acids and bases?. Bronsted-Lowry Acid

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Acids and Bases

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  1. Acids and Bases

  2. What are acids 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

  3. What are acids and bases? • Bronsted-Lowry Acid • A hydrogen-ion donor • Bronsted-Lowry Base • A hydrogen-ion acceptor

  4. What are acids and bases? • 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)

  5. What are 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

  6. What are acids and bases?

  7. Strong vs. Weak 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

  8. Strong vs. Weak Acids and Bases • 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

  9. Naming Acids • Single Element: • Hydro_____ic acid • Ex: HCl = Hydrochloric acid • Polyatomic Ion: • ATEic ITEous • Ex: H2SO4 = sulfuric acid • Ex: H2SO3 = sulfurous acid

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

  11. Hydrogen Ions from Water • 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+)

  12. Dissociation of Water • 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)

  13. Dissociation of Water • 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

  14. Concentrations • 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-]

  15. pH • 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

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

  17. Measuring pH • Acid-Base Indicators • 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

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

  19. Titrations • If the mole ratio is known, you can calculate the concentration of a given acid or base • nAA + nBB products • This means that nA moles of A reacts with nB moles of B

  20. To work out concentration CA (moldm-3) of unknown solution A of volume VA (dm-3) at the end of the titration: CA x VA = nA CB x VB = nB E.g. CA = nA X CB x VB nB x VA

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