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Ch. 20 Acids and Bases
Observable Properties of Acids and Bases
• Sour Taste• Electrolytes when in
aqueous solution• React with metals to
produce Hydrogen gas• React with hydroxide
ions to produce water and salt
• Bitter Taste• Feel “slippery”• React with acids to form
water and Salt
Electrolytes: Conduct electricity through their dissociation into ions
pH Scale
pH = - log [H+]• Measures the concentration of
Hydrogen ions in solution• The lower the pH number, the
higher the amount of Hydrogen ions in solution.
pH + pOH = 14
pH 1 2 3 4 5 6 7 8 9 10 11 12 13 14Acidic BasicAlkali Neutral
Alkaline
pH = - log [H+]
1 x 10-2 M has a pH 2
When written in scientific notation with a coefficient of 1, the absolute value of the exponent is the pH value of the solution.
What is the pH of 1 x 10-5 M solution?
pH = - log [H+]Calculate the pH of a solution that has a hydrogen ion concentration of 4.3 x 10-8 M.
pH = - log [H+]Calculate the pH of a solution that has a hydrogen ion concentration of 4.3 x 10-8 M. pH = - log [H+]pH = - log (4.3 x 10-8)pH = - (log 4.3 + log 10-8)pH = - (0.633) – (-8)pH = 7.367
Your Turn. pH = - log [H+]
Calculate the pH of a solution that has a hydrogen ion concentration of 2.0 x 10-5 M.
pH = 4.7
Calculating pOHpOH = - log [OH-]
Plug and chug using the same order of operations as the pH problem solving!
** You may be asked to solve for pH when given a hydroxide ion concentrationRemember that pH + pOH = 14How would you go about solving this problem?
Measuring pH• Acid Base Indicators– Color Change:
Red = acidic Blue = basic
Measuring pH
• pH Meters or pH Probes
Acids:
• Hydrogen Ion donating
Bases:
• Hydrogen ion accepting
NH3 (aq) + H2O(l) NH4+ (aq) + OH-(aq)
Strong Acids and Bases
Fully dissociate in solution to their ionic forms
HCl H+ + Cl-
Weak Acids and Bases: Partially dissociate
pH Titration Curves
Time to Practice!!!