chapter 25 lesson 2 strengths of acids and bases
TRANSCRIPT
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CHAPTER 25Lesson 2Strengths of Acids and Bases
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STRONG AND WEAK ACIDS AND BASES • The strength of an acid or base depends
on how many acid or base particles dissociate into ions in water.
• Strong Acid/Base– 100% ions in water– strong electrolyte– HCl, HNO3, NaOH, LiOH
• Weak Acid/Base• few ions in water• weak electrolyte• HC2H3O2, NH3
- +
- +
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STRONG AND WEAK ACIDS• Equations describing dissociation
can be written in two ways.
• In strong acids, such as HCl, nearly all the acid dissociates.
• This is shown by writing the equation using a single arrow pointing toward the ions that are formed.
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STRONG AND WEAK ACIDS• Equations describing the
dissociation of weak acids, such as acetic acid, are written using double arrows pointing in opposite directions.
• This means that only some of the CH3COOH dissociates and the reaction does not go to completion.
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STRONG AND WEAK BASES• A strong base dissociates
completely in solution
• The following equation shows the dissociation of sodium hydroxide, a strong base.
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STRONG AND WEAK BASES• This dissociation of ammonia, which
is a weak base, is shown using double arrows to indicate that not all the ammonia ionizes. It only produces a few ions in water.
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PH OF A SOLUTION• The pH of a solution is a measure of
the concentration of H+ ions in it.
• The greater the H+ concentration is, the lower the pH is and the more acidic the solution is.
• The pH measures how acidic or basic a solution is.
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PH SCALE
0
7INCREASINGACIDITY
NEUTRAL INCREASINGBASICITY
14
• pH–a measure of the concentration of
H3O+ ions in solution
–measured with a pH meter or an indicator with a wide color range
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PH SCALE
pH of Common SubstancespH of Common Substances
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STRENGTH AND CONCENTRATION• In contrast, the terms dilute and concentrated are used to indicate the concentration of a solution, which is the amount of acid or base dissolved in the solution.
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• It is possible to have dilute solutions of strong acids and bases and concentrated solutions of weak acids and bases
STRENGTH AND CONCENTRATION
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BLOOD PH• In order to carry out its many
functions properly, the pH of blood must remain between 7.0 and 7.8.
• The main reason for this is that enzymes, the protein molecules that act as catalysts for many reactions in the body, cannot work outside this pH range.
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BLOOD PH• Your blood contains compounds
called buffers that enable small amounts of acids or bases to be absorbed without harmful effects.
• Buffers are solutions containing ions that react with additional acids or bases to minimize their effects on pH.
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• Which of the following "molecular" pictures best represents a concentrated solution of the weak acid HA?
CONCEPTEST
A B
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• Is the following statement TRUE or FALSE?
–A strong acid has a lower pH than a weak acid.
–TRUE - Strong/weak refers to amount of ionization whereas pH refers to concentration of H+.
CONCEPTEST