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Acids, Bases, and pH: Common Substances and Properties

Learn about common acids and bases encountered in daily life and their properties. Understand the distinction between acids and bases through simple observable properties. Discover acid-base indicators and their color changes. Explore reactions involving acids and bases.

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Acids, Bases, and pH: Common Substances and Properties

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  1. Chapter 14: Acids, Bases, and pH Section 14.1: Acids and Bases

  2. Acids and Bases What are some common acids and bases that you encounter everyday? • Acid-Base chemistry plays an important role in many processes • Substances classified as acids or bases can be considered opposites • Simple, observable properties distinguish the two

  3. Litmus test Reliable indicator of acid or base • Based on color change • when mixed with acid, litmus is red • when mixed with base, litmus is blue

  4. ACIDS • Substance that produces hydronium ions when dissolved in water • A hydronium ion, H3O+, consists of a hydrogen ion attached to a water molecule • Acids are sometimes called proton donors (gives up a H+)

  5. Properties of Acids • Taste sour • Litmus dye (acid-base indicator) is red • Corrode most metals • React with carbonates to form CO2 gas

  6. Properties of Acids (cont) Acids are electrolytes: • Because acids ionize to form ions in water, acidic solutions conduct electricity

  7. Base • Substance that produces hydroxide ions, OH-, when dissolved in water • Bases are sometimes called proton acceptors (accept a H+)

  8. Properties of Bases • Taste bitter • Feel slippery • Litmus dye is blue • Do not commonly react with metals • Do not react with carbonates

  9. Properties of Bases (cont) Bases are electrolytes: • Because bases in water produce ions, aqueous solutions of bases will conduct electricity

  10. Acid-base indicators Color will change based on the whether substances are acids or bases. Common materials • Litmus • red cabbage • radishes • tulips • rose petals

  11. Acid with Water • The reaction of an acid with H2O is a transfer of a hydrogen ion, H+, from an acid to a H2O molecule • This transfer forms the positively charged hydronium ion, H3O+, and a negatively charged ion Example: HCl(g) + H2O(l) → H3O+ + Cl-

  12. ACIDIC HYDROGEN • In an acid, the hydrogen atom that is transferred to water • It is possible for acids to have more than one acidic hydrogen per molecule • To distinguish acids from other hydrogen-containing molecules, acidic hydrogens are written first in the formula

  13. ACIDIC HYDROGEN • Anytime hydrogen is the first element in a formula of a compound, the substance is an acid • Protic- remaining proton- indicates how many acidic hydrogens are present in an acid Monoprotic acids: HCl (hydrochloric acid) HC2H3O2 (acetic acid) Polyprotic acids: Diprotic acid:Triprotic acid: H2SO4 (sulfuric acid)H3C6H5O7 (citric acid)

  14. Which Hydrogen is Acidic? Hydrogen fluoride Acetic Acid Benzene

  15. Chemical Reaction Shorthand HA = any monoprotic acid H+ = hydronium ion A- = negatively charged ion Water is not shown as participating in the reaction Example: H2SO4(aq) → H+(aq) + HSO4-(aq) can be written as: H2A(aq) → H+(aq) + HA-(aq) HA-(aq) → H+(aq) + A2-(aq)

  16. IONIZATION • The process of forming ions in a solution is called ionization. • In a reaction of an acid with water, ions are formed in a process called acid ionization. • Because of this ionization, acidic solutions conduct electricity - Acids are electrolytes • They range from strong to weak conductors HCl strong HC2H3O2 weak

  17. Acids with Metals Acids react with metals that are more active than hydrogen to form both a compound of the metal and hydrogen gas. General: X +HA → XA + H2 (X = metal) Examples: Fe + 2HCl → FeCl2 + H2 Li + 2HBr → LiBr + H2

  18. Acids with Carbonates Acids react with carbonates (contains CO3-2 ions) to form carbon dioxide and water • 2 Products are CO2 and H2O Examples: HC2H3O2 + CaCO3 → CO2 + H2O + Ca(C2H3O2)2 HCl + CaCO3 → CO2 + H2O + CaCl2

  19. Bases produce electrolytes There are two mechanisms by which bases produce hydroxide ions when they dissolve in water.

  20. 1. Simple bases: metal hydroxides OH- is formed by simple ionic dissociation • No transfer occurs between the base and the water molecules to form the hydroxide ion Example: NaOH → Na+ + OH-

  21. 2. Reversing the transfer: bases that accept H+ Some bases (covalent compounds), produce OH- by an ionization process dissolved in water  • Transfer of a hydrogen ion from water to the base Example: NH3(g) + H2O(l) → NH4+(aq) + OH-(aq)

  22. Chemical Reaction Shorthand B = Covalent base Example: NH3(g) + H2O(l) → NH4+(aq) + OH-(aq) can be written as B + H2O(l) → BH+(aq) + OH-(aq)

  23. Anhydrides • Oxides (oxygen bonded to just one other element) that contain no water •  Anhydrides act as acids and bases (in both reactions water is the active reactant) Acidic Anhydrides: nonmetal oxides that are covalent compounds and will form an acid in water Basic Anhydrides: metal oxides that are ionic compounds and will form a base in water

  24. Anhydrides (cont) ACIDIC ANHYDRIDES Examples: CO2, SO2, NO2 CO2 + H2O → H2CO3  SO2 + H2O → H2SO4 BASIC ANHYDRIDES Examples: CaO, Na2O CaO + H2O → Ca(OH)2 Na2O + H2O → 2NaOH

  25. Acid Rain Acidic anhydrides and acid rain: • CO2 is a familiar acidic anhydride • CO2 dissolves in rainwater, forming carbonic acid (H2CO3) Acidity of normal rain does not damage the environment However, when sulfur oxides, nitrogen oxides, and increased amounts of carbon dioxide dissolve in rain, acid-forming reactions produce acid rain

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