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AP Chemistry Unit 10 – Acids and Bases

AP Chemistry Unit 10 – Acids and Bases. Lesson 9 – Molecular Structure and Acid/Base Properties Book Section: 16.10. Hydride Bases. We are used to seeing hydrogen ions (H + ) as acids… but there are a class of compounds called hydrides (H - ), which act as bases. Ex: NaH (ionic bond w/ H - )

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AP Chemistry Unit 10 – Acids and Bases

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  1. AP ChemistryUnit 10 – Acids and Bases Lesson 9 – Molecular Structure and Acid/Base Properties Book Section: 16.10

  2. Hydride Bases • We are used to seeing hydrogen ions (H+) as acids… but there are a class of compounds called hydrides (H-), which act as bases. • Ex: NaH (ionic bond w/ H-) • We will learn more about why these are bases when we discuss the Lewis definition of acids/bases.

  3. Acid Strength • In an acid, the strength of the bond between the acidic hydrogen and the other atom (H-X) determines how strong the acid is. • In general, the strength of an H-X bond weakens as atoms get bigger. • So, going down a group, the strength of an acid increases. • HF < HCl < HBr < HI

  4. Acid Strength • Going across a row, bond strengths don’t change all that much. So, bond polarity is the major factor – the more polar the bond, the stronger the acid • Period 2: CH4 < NH3 < H2O < HF

  5. Acid Strength

  6. Oxyacids • In an oxyacid (w/ polyatomic ion like SO42-), there are often many –OH groups. Why do these –OH groups act like acids instead of bases? • If the central atom is electronegative, the oxygen stays attached to the ion, releasing H+, instead of releasing a hydroxide ion.

  7. Oxyacids • The more electronegative the central atom, the stronger the acid. • HClO3 > HBrO3 > HIO3

  8. Oxyacids • If the acids have the same central atom, the higher the oxidation state of the central atom, the stronger the acid • AKA: The more oxygens attached to the central atom, the stronger the acid. • HClO < HClO2 < HClO3 < HClO4

  9. Carboxylic Acids • On a similar note, carboxylic acids contain –OH groups, but are acids, because of the additional attached oxygen “aldehyde” group on the final carbon in the chain. • Carboxylic acids are also stabilized by resonance once the hydrogen goes away.

  10. HW: 16.92, 94, 96, 98 • Next week: • Monday: Titration 3 Lab • Tuesday: Lewis Acids & Bases (16.11) • Wednesday: Begin Unit 11: Additional Equilibrium Topics: The Common Ion Effect (17.1) • Thursday: Buffers (17.2) • Friday: Determining an Equilibrium Constant Using a Spectrophotometer Lab • Titration 2 Due Mon 3/14 • Rate Law Due Wed 3/16 • Problem Set 9 – 3/21 • Acid/Base Exam: 3/22

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