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Acids/Bases

This article explores the definitions and properties of acids and bases, including their effects on taste, electrolyte properties, and reactions with each other. It also discusses the self-ionization of water and the ion-product constant (Kw) that determines the acidity or basicity of a solution. Examples are provided to illustrate calculations involving hydrogen and hydroxide ion concentrations.

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Acids/Bases

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  1. Acids/Bases • Svante Arrhenius, a Swedish chemist, proposed the following definition: • Acids form hydronium ions in aqueous solutions, while bases form hydroxide ions. • Acids give off H+ • Bases give off OH-

  2. Properties of acids • Give foods a tart or sour taste • Electrolytes • React with hydroxide ions to form water and a salt • HCl + NaOH --> NaCl + H2O

  3. Properties of bases • React with acids to form water and salt • Have a bitter taste • Have a slippery feel • Electrolytes • Milk of Magnesia (Magnesium Hydroxide) is a base used to treat excess stomach acid problems.

  4. Hydrogen Ions from WaterThis is the basis to start understanding pH • Water is considered neutral • Collision between water molecules can cause a hydrogen ion to transfer from one molecule to another. H2O H2O H3O+ OH- hydronium ion hydroxide ion

  5. Self-Ionization of Water Water self ionizes to the concentration of 1.0 x 10-7 mol/L. When the concentration of each ion equals 1.0 x 10-7 mol/L the solution is said to be neutral Therefore, since water is considered neutral the concentrations of the ions can be calculated through the Ion product constant.

  6. The Ion-Product ConstantKw • Notation • [H+] - concentration of hydrogen ions • Or hydronium ions • [OH-] - concentration of hydroxide ions • When [H+] and [OH-] are multiplied we get the ion-product constant. • Kw = [H+] x [OH-] = 1.0 x 10-14 (mol/L)2 or M2 • This is an inverse relationship. • One goes up, the other goes down.

  7. The Ion-Product ConstantKw example problem • If [H+] = 1.0 x 10-5 mol/L, is the solution acidic, basic, or neutral? What is the [OH-] of this solution? • Answer • Acidic - the [H+] is greater than 1.0 x 10-7 mol/L • 1.0 x 10-5 mol/L x [OH-] = 1.0 x 10-14 M2 • [OH-] = 1.0 x 10-9 mol/L

  8. The Ion-Product ConstantKw example problem • If [OH-] = 2.8 x 10-8 mol/L, is the solution acidic, basic, or neutral? What is the [H+] of this solution? • Answer • acidic - the [OH-] is less than 1.0 x 10-7 mol/L • [H+] x 2.8 x 10-8 mol/L = 1.0 x 10-14 M2 • [H+] = 3.5 x 10-7 mol/L

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