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Unit 12: Acids and Bases

Unit 12: Acids and Bases. Section 2: pH and pOH Scales. The pH Scale. pH: The negative of the common logarithm of the hydronium ion concentration [H 3 O + ] pH stands for the French words pouvoir hydrogene , meaning “hydrogen power” pH = -log [H 3 O + ]

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Unit 12: Acids and Bases

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  1. Unit 12: Acids and Bases Section 2: pH and pOH Scales

  2. The pH Scale • pH: The negative of the common logarithm of the hydronium ion concentration [H3O+] • pH stands for the French words pouvoirhydrogene, meaning “hydrogen power” • pH = -log [H3O+] • A neutral solution at 25°C (room temperature) has a [H3O+] of 1x10-7 M • pH = -log [H3O+] = -log (1x10-7) = -(-7) = 7

  3. The pOH Scale • pOH: The negative of the common logarithm of the hydroxide ion concentration [OH-] • pOH = -log [OH-] • A neutral solution at 25°C has a [OH-] of 1x10-7 M • pOH = -log [OH-] = -log (1x10-7) = -(-7) = 7 • pH + pOH = 14

  4. Sample Problems • What is the pH of a 1.0x10-3 M HCl solution? • pH = -log (1.0x10-3) = 3 • The pH is 3! • What is the pOH of a 1.0x10-3 M HCl solution? • Because HCl is an acid, we must first find pH • pH = -log (1.0x10-3) = 3 • To find pOH we need to subtract pH from 14 • 14 – pH = pOH • 14 – 3 = 11 • pOH is 11!

  5. Sample Problems • What is the pH of a 1.0x10-3 M NaOH solution? • Because NaOH is a base, we must first find pOH. • pOH = -log (1.0x10-3) = 3 • To find pH we need to subtract pOH from 14. • 14 – pOH = pH • 14 – 3 = 11 • The pH is 11!

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