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Strength of Acids and Bases

Strength of Acids and Bases. Chapter 8 Section 8.4. The pH Scale. We use this scale to measure the strength of an acid or base. pH can use the concentration of hydronium ions or hydrogen ions pH can be measured with a pH meter or an indicator with a wide color range. The pH scale.

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Strength of Acids and Bases

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  1. Strength of Acids and Bases Chapter 8 Section 8.4

  2. The pH Scale • We use this scale to measure the strength of an acid or base. • pH can use the concentration of hydronium ions or hydrogen ions • pH can be measured with a pH meter or an indicator with a wide color range.

  3. The pH scale • The pH scale is a way of expressing the strength of acids and bases. Instead of using very small numbers, we just use the NEGATIVE power of 10 on the Molarity of the H+/H3O+(or OH-) ion.Under 7 = acid 7 = neutralOver 7 = base

  4. pH Scale pH of Common Substances

  5. Acid – Base Concentrations 10-1 pH = 3 pH = 11 OH- H3O+ pH = 7 10-7 concentration (moles/L) H3O+ OH- OH- H3O+ 10-14 [H3O+]<[OH-] [H3O+]>[OH-] [H3O+]=[OH-] acidic solution neutral solution basic solution

  6. Strong Acids and Bases • Acids that ionize completely are called strong acids. • The strength of an acid is determined by the amount of ionization. • Bases that dissociatealmost completely into its ions are called strong bases.

  7. List of Strong Acids • HCl – hydrochloric acid • HNO3– nitric acid • HClO4 – perchloric acid • H2SO4 – sulfuric acid

  8. List of Strong Bases • NaOH – Sodium Hydroxide • Ca(OH)2 - Calcium Hydroxide • KOH – Potassium Hydroxide • LiOH – Lithium Hydroxide

  9. Weak Acids and Bases • An acid that only slightly ionizes in a water solution is called a weak acid. • Weak acids have only a small percent of acid molecules that donate their hydrogen, and most remain the same. • Weak acids have a higher pH than a strong acid of the same concentration. (Remember concentration is he amount of solute dissolved in a given amount of solution) • A base that dissociates only slightly in a water solution is a weak base. • In these reactions the equilibrium favors the reactants over the products, so few ions form in the solution.

  10. List of Weak Acids and Bases • C2H4O2 – Acetic Acid • CH2O2 – Formic Acid • NH3 - Ammonia • NH4OH - Ammonium hydroxide

  11. Buffers • Buffers are solutions in which the pH remains relatively constant, even when small amounts of acid or base are added • Buffered solutions contain either: • A weak acid and its salt • A weak base and its salt

  12. Buffers • The operation of a buffer depends on a shift in equilibrium to counteract any changes in pH. • Buffers are used in products and processes where the pH of the solution needs to be controlled. • Examples: Shampoo, Medicine, and Fermentation • Our blood is a buffer, its pH is about 7.4

  13. Electrolytes • Substances whose molecules dissociate into ions when they are placed in water. • CATIONS (+) ANIONS (-) • Electrolyteisa substance that when dissolved in water conducts electricity • Strong electrolyte = completely ionized or dissociated; strongly conductive solution • Weak electrolyte = partially ionized or dissociated; somewhat conductive solution

  14. Electrolytes • Many salts (ionic compounds) are strong electrolytes • Strong Acids are strong electrolytes • Strong Bases are strong electrolytes • In contrast, weak acids, weak bases are weak electrolytes.

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