Acids, Bases, and Salts

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Acids, Bases, and Salts

• Module 6

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Acids

• Acids produce hydronium ions (H3O) or hydrogen
  ions (H) when they are dissolved in aqueous
  solutions
• They turn blue litmus paper red
• Litmus paper is used as an indicator to identify
  acidic and basic substances
• They are electrolytes
• They neutralize bases by reacting with them to
  produce a salt and water (neutralization
  reaction)
• They have a sour taste

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Bases

• Bases produce the hydroxide ion (OH-) when
  dissolved in aqueous solutions
• They turn red litmus paper blue
• Like acids, they are electrolytes
• They react with acids in neutralization reactions
• They have a bitter taste
• They have a slippery or soapy feel

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General Formulas for Acids and Bases

• Acids
• Hydrogen is present, and is written first
• The second ion is a non-metal ion or a polyatomic
  ion
• HX

• Bases
• The hydroxide ion is present, and is written
  second
• The first ion is a metal ion or the ammonium ion
• MOH

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Strong and Weak Acids and Bases

• Strong acids and strong bases are strong
  electrolytes, meaning that they completely
  dissociate into ions when dissolved in water
• Strong acids HCl (hydrochloric acid), HBr
  (hydrobromic acid), HI (hydroiodic acid), HNO3
  (nitric acid), H2SO4 (sulfuric acid), HClO4
  (perchloric acid), HBrO4 (perbromic acid), HIO4
  (periodic acid)
• Some strong bases Group 1A hydroxides (LiOH,
  NaOH, KOH, RbOH, CsOH), Ca(OH)2, Sr(OH)2, Ba(OH)2
• Weak acids and weak bases are weak electrolytes,
  meaning that they dissociate into ions less than
  50 when dissolved in water
• If an acid or a base is not considered a strong
  acid or base, then it is considered a weak acid
  or base
• Ammonia (NH3) is a weak base, even though it
  doesnt contain hydroxide (OH-) ions, since it
  does produce hydroxide ions when it dissolves in
  water

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Ionization of Water

• A water molecule can react with another water
  molecule to produce two ions a hydronium ion
  (H3O) and a hydroxide ion (OH-)
• A simplified version of the reaction (the forward
  reaction)
• H2O -gt H OH-
• The reverse of this reaction also occurs
• H OH- -gt H2O
• Since both the forward and reverse reactions
  occur, the reaction is an equilibrium for every
  mole of water molecules, only 1 10-7 moles
  dissociate to produce the same concentration of
  hydrogen ions and hydroxide ions
• The molarity (molar concentration (M
  moles/liter)) of hydrogen ions and hydroxide ions
  in pure water at 25C
• H 1 10-7 M and
  OH- 1 10-7 M

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pH

• The pH scale expresses acid and base
  concentrations
• It ranges from 0 to 14
• pH 0 to 7 (i.e. less than 7) are acids
• pH 7 are neutral solutions
• pH 7 to 14 (i.e. more than 7) are bases

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Calculations with pH and pOH

• pH is the negative logarithm of the hydronium ion
  or hydrogen ion
• pH -log H OR H 10-pH
• pOH is the negative logarithm of the hydroxide
  ion
• pOH log OH- OR OH- 10-pOH
• pH pOH 14

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Examples of Calculations with pH and pOH

• Example 1 What is the pH, pOH, OH- of H
  10-3? Is it an acid, a base, or neutral?
• pH - log H -log (10-3) 3
• Hint pH negative of the power of ten
• pH pOH 14 ? pOH 14 pH 14 3 11
• OH- 10-pOH 10-11
• Since the pH 3, it is an acid

• Example 1 What is the H, pOH, OH- of pH
  8? Is it an acid, a base, or neutral?
• H 10-pH 10-8
• pH pOH 14 ? pOH 14 pH 14 8 6
• OH- 10-pOH 10-6
• Since the pH 8, it is a base

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Comparison of pH and pOH and their corresponding
H and OH- values
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Neutralization Reactions

• A neutralization (acid-base) reaction occurs when
  equal quantities of an acid and a base react with
  each other to produce a salt and water
• Steps to complete and balance a neutralization
  reaction
• Combine H and OH- to form water
• Combine the anion (the negative ion) from the
  acid and the cation (the positive ion) from the
  base to form the salt, always writing the cation
  first
• Check to see if the salt has the correct chemical
  formula (i.e. that the salt is neutral, that
  the charge on the anion balances the charge on
  the cation) add subscripts if needed
• Balance the entire equation (acid base -gt water
  salt) with the general rules for balancing
  chemical equations

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Example 1 of Completing and Balancing a
Neutralization Reaction

• Complete and Balance H3PO4 NaOH
• Form H2O
• H3PO4 NaOH ? H20
• Form salt
• H3PO4 NaOH ? H20 NaPO4
• Check salt formula
• Na group 1, so forms 1 ion AND PO4 -3 ion
• Correct formula Na3PO4
• Balance entire equation
• __ H3PO4 _3_ NaOH ? _3_ H20 __ Na3PO4
• Polyatomic ions PO4 1 and 1
• Elements in only one compound Na 1 and 3 ? 3
  and 3 O 3 and 1 ? 3 and 3
• Elements in more than one compound H 6 and 6
• Double check balancing

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Example 2 of Completing and Balancing a
Neutralization Reaction

• Complete and Balance HNO3 Mg(OH)2
• Form H2O
• HNO3 Mg(OH)2 ? H20
• Form salt
• HNO3 Mg(OH)2 ? H20 MgNO3
• Check salt formula
• Mg group 2, so forms 2 ion AND NO3 -1 ion
• Correct formula Mg(NO3)2
• Balance entire equation
• _2_ HNO3 __ Mg(OH)2 ? _2_ H20 __ Mg(NO3)2
• Polyatomic ions NO3 1 and 2 ? 2 and 2
• Elements in only one compound Mg 1 and 1 O
  2 and 1 ? 2 and 2
• Elements in more than one compound H 4 and 4
• Double check balancing

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Buffers

• A buffer solution is a solution whose pH remains
  relatively constant (i.e. doesnt change much)
  when either an acid or a base is added to it
• Buffers are important because when even just a
  small amount of an acid or a base is added to
  water, a drastic change in the pH of the water
  occurs
• Buffers resist pH changes only to a certain
  extent i.e. they dont have an unlimited
  capacity for resisting pH changes
• Buffers have two components
• One component reacts with any excess acid that is
  added
• The other component reacts with any excess base
  that is added
• Acidic Buffers a weak acid and its salt
• Example H2CO3 (carbonic acid) and NaHCO3 (the
  salt of carbonic acid)
• Basic Buffers a weak base and its salt
• Example NH3 (ammonia) and NH4Cl (the salt of
  ammonia)

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Buffers in the Body The Blood Buffer 1

• Carbon dioxide (CO2) is an end product of
  cellular metabolism
• Some CO2 is carried by the red blood cells to the
  lungs, where it is eliminated from the body
• The rest is dissolved in the aqueous medium of
  the blood, where it reacts with water to produce
  carbonic acid (H2CO3)
• Carbonic acid is a weak acid that can dissociate
  into hydrogen ions and bicarbonate ions (HCO3-),
  thus producing an acidic buffer (H2CO3 HCO3-)

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Buffers in the Body The Blood Buffer 2

• If base (OH-) is added to the blood buffer, it
  reacts with the weak acid, H2CO3, to produce
  HCO3- (1)
• If acid (H) is added to the blood buffer, it
  reacts with the bicarbonate ions, HCO3-, to
  produce H2CO3 (2)

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Acidosis and Alkalosis

• The pH of the blood is maintained by a series of
  reactions that are at equilibrium (i.e. the
  forward and reverse reactions are taking place at
  the same rate and as long as nothing is done to
  the system, the concentration of all the
  components remains the same)
• The capacity of the blood buffer is limited
• If more acid is added than the buffer can take,
  causing the pH to drop below 7.35, acidosis
  occurs
• If more base is added than the buffer can take,
  causing the pH to rise above 7.35, alkalosis
  occurs

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Le Chatliers Principle

• Le Chateliers Principle if an external stress
  is applied to a system that is at equilibrium,
  the system will react in such a way to relieve
  the stress in order to reestablish equilibrium
• For example
• If the concentration of one component is
  increased, the equilibrium will shift to decrease
  the amount of that component, so it will shift
  towards the side the component is NOT on
• If the concentration of one component is
  decreased, the equilibrium will shift to increase
  the amount of that compounent, so it will shift
  towards the side the component is on

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Respiratory Acidosis

• Respiratory acidosis is acidosis caused by
  respiratory problems
• It is caused by an increase in carbon dioxide
  (CO2) in the blood due to a defect of the
  respiratory center of the medulla of the brain or
  improper gas diffusion
• To compensate for the increase in CO2, the
  production of H is increased, which causes the
  pH to decrease
• Symptoms breathing suppression, disorientation,
  weakness, coma
• Causes some lung diseases, poorly ventilated
  rooms, cardiopulmonary arrest, stroke, nervous
  system disorders
• Treatment correction of disorder, infusion of
  bicarbonate

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Respiratory Alkalosis

• Respiratory alkalosis is alkalosis caused by
  respiratory problems
• It is caused by a decrease in carbon dioxide
  (CO2) in the blood due to exhaling too much
• To compensate for the decrease in CO2, the
  production of CO2 and H2O increases, which
  decreases the production of H, which causes the
  pH to increase
• Symptoms increased rate and depth of breathing,
  numbness, light-headedness
• Causes hyperventilation due to anxiety, fever,
  hysteria, exercise
• Treatment elimination of anxiety-producing
  state, breathing into a paper bag

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Metabolic Acidosis

• Metabolic acidosis occurs when there is an
  increased acid level in the blood, which thus
  drops the pH of the blood
• Acids are present in the body from metabolic
  reactions or from ingesting them
• If the excess acid is not neutralized fast enough
  by the blood buffers or eliminated by the
  kidneys, then the production of H increases,
  which causes a decrease in pH
• Symptoms increased ventilation, fatigue,
  confusion
• Causes renal disease, diarrhea, alcoholism,
  starvation, diabetes mellitus, kidney failure
• Treatment oral dose of sodium bicarbonate,
  dialysis for renal failure, insulin treatment for
  diabetes

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Metabolic Alkalosis

• Metabolic alkalosis occurs when there is too
  little acid present in the body or when there is
  too much base present in the body
• If too much acid is lost by the body or if too
  much base is ingested by the body, then the
  production of H decreases, which causes an
  increase in pH
• Symptoms depressed breathing, apathy, confusion
• Causes vomiting, ingestion of excess base
• Treatment infusion of saline solution,
  treatment of the underlying diseases