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Understanding Acids and Bases: Properties, pH Scale, and Neutralization

This note provides an overview of acids and bases, including key properties, the pH scale, and the process of neutralization. Acids are characterized by the presence of hydrogen ions (H+) and typically have a sour taste, turning litmus paper red. Bases contain hydroxide ions (OH-) and are bitter, turning litmus paper blue. The pH scale measures the concentration of H+ ions, ranging from 0 (very acidic) to 14 (very basic). Neutralization reactions between acids and bases produce water and salts. Additionally, titration is a method used to achieve neutralization.

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Understanding Acids and Bases: Properties, pH Scale, and Neutralization

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  1. Acids and Bases Notes Spring 2011

  2. What is an acid or base? • A solution! • Acid Solute: hydrogen ions (H+) • Base Solute: hydroxide ions (-OH) • Solvent: water

  3. The pH scale • used to measure hydrogen ions (H+) • pH = “power of hydrogen” • Litmus Test: • pH < 7 is an ACID • 7 is NEUTRAL (6.5 - 7.5) • pH > 7 is a BASE LITMUS PAPER

  4. Properties of acids • Have hydrogen ions (H+) • Have a sour or tangy taste • Acids are electrolytes: they have dissolved ions that conduct electricity • Turn litmus paper red • Ex: fruits, coffee, vinegar

  5. Properties of Bases • Have hydroxide (OH-) ions • Have a bitter taste • Are electrolytes • Turn litmus paper blue • Ex: shampoo, detergent, antacids

  6. Strong vs. Weak • A strong solution is (lots of solute) is close to the edge of the pH scale • Strong = more dangerous • Strong Acids = pH 0 - 1 • Strong Bases = pH 13 - 14

  7. Indicators • Dyes that turns colors based on pH • weak acids or weak bases • Universal indicator is a mix of several

  8. Litmus Paper • Red = acid • Blue = base

  9. Phenolphthalein • Clear in acids • Pink > pH 8

  10. Universal Indicator • A mix of several indicators • Changes color at each pH

  11. Common Indicators

  12. ACID The pH scale • measure hydrogen ion (H+) content • pH = “power of hydrogen” • range from 0 to 14 • 0 = very acidic • 14 = very basic BASE

  13. ACID 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 The pOH scale • Power of –OH (hydroxide) • How basic something is depends on hydroxide ion (OH-) concentration • OPPOSITE OF pH! • 0 = very basic • 14 = very acidic BASE

  14. pH and pOH • equation for switching between pH and pOH scales: pH + pOH = 14

  15. Formulas pH= -log [H+] 10(-pH) = [H+] pOH= -log [OH-] 10(-pOH) = [OH-]

  16. What is neutralization? • double-replacement reaction between an acid and a base • products are water and a salt • Salts are ionic compounds: • cation from a base • anion from an acid

  17. General Equation: Acid + Base  Salt + H2O -or- HX + QOH QX + HOH acid base salt water

  18. Titration • Neutralization is done by titration • drop-by-drop mixing of acid and base until the solution is neutral (pH = 7)

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