NOTES 10

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NOTES 10 Acids, Bases, pH
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Ion Review

• An ion is an atom that gains or loses electrons
  giving it an overall positive or negative charge
• Lose electrons positively charged ion
• Gain electrons negatively charged ion
• Sometimes a compound acts like an ion
• Hydrogen atoms have 1 proton and 1 electron
• Compounds that take hydrogens electron can
  become negative ions (more electrons than
  protons)
• The leftover hydrogen proton becomes a positive
  hydrogen ion

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Water Molecules Form Ions

• Water molecules break apart into ions and then
  reform into molecules
• Water forms two different ions
• Hydrogen Ions H
• Hydroxide Ions OH-
• H2O ?? H OH-
• When water breaks into ions, it is called
  dissociation (Water dissociates into ions)
• In pure water there are equal numbers of hydrogen
  and hydroxide ions

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Dissociation of Water

• In any sample of water, very few of the molecules
  are dissociated at any one time
• About 1 in 550 million 
• There is constant change
• As one hydrogen ion reattaches to a hydroxide ion
  to form a water molecule, another water molecule
  dissociates to replace the hydrogen ion and the
  hydroxide ion in solution

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What are acids?

• Acid a compound that increases the number of
  hydrogen ions (H) when dissolved in water
• In water, acids dissociate producing H ions
• Acidic solutions (acid substance water) have
  more hydrogen ions than hydroxide ions (More H
  than OH-)
• Acids taste sour
• Acids can cause burns
• Acids can be good conductors of electricity
• EX. acetic acid, citric acid, ascorbic acid

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Strong Vs. Weak Acids

• Strong acids ionize completely
• Every molecule of the acid produces H ions and
  negative acid ions
• Strong acids have a pH in the range of 0 to 3
• EX. Nitric acid in water
• HNO3 ? H NO3-
• Weak acids do not ionize completely
• Some molecules form ions, some do not
• Weak acids have a pH above 3
• EX. Acetic acid in water
• CH3COOH ?? CH3COO- H

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Acids Are Useful But Can Be Dangerous

• Acids are used for cleaning, in batteries, making
  fertilizers, dyes, etc.
• Foods contain acids (vinegar citrus fruits)
• Stomach acid helps digest your food
• Acids in concentrated forms can cause severe skin
  damage
• Acid vapors can damage the eyes, mouth, and lungs

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What are bases?

• Base a compound that increases the number of
  hydroxide ions (OH-) when dissolved in water
• In water, bases dissociate producing OH- ions
• Basic solutions (base substance water) have
  more hydroxide ions than hydronium ions (More OH-
  than H)
• Bases taste bitter
• Bases feel slippery and may cause burns
• EX. baking soda, bleach, ammonia

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Strong Vs. Weak Bases

• Strong bases are ionic compounds that contain
  hydroxide ions (OH-)
• When dissolved in water, a strong base
  dissociates (separates) forming hydroxide ions
• EX. Sodium hydroxide in water
• NaOH ? Na OH-
• Weak bases do not contain hydroxide ions, but
  form them when mixed with water
• EX. Ammonia and water
• NH3 H2O ?? NH4 OH-

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Bases Are Useful But Can Be Dangerous

• Bases are used to make soaps, to clean drains, to
  make cement, fertilize soil, etc.
• Bases attack living tissue very quickly
• In concentrated form, bases can be very harmful
• Even in diluted form, some bases can be fairly
  dangerous

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Acids, Bases, Electricity

• Strong acids and strong bases are good conductors
  of electricity (electrolytes)
• Electrolyte a substance that dissolves in water
  forming a solution that conducts electricity
• EX. A solution of sulfuric acid and water
  conducts electric current in car batteries

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What is pH?

• pH a number used to indicate how acidic or
  basic a solution is
• The pH scale goes from 0 to 14
• Solutions with a pH below 7 are acids
• Lower number stronger acid
• EX. A solution with a pH of 2 is a stronger acid
  than a solution with a pH of 5

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What is pH?

• Solutions with a pH above 7 are bases
• Higher number stronger base
• EX. A solution with a pH of 13 is a stronger base
  than a solution with a pH of 9
• Pure water has a pH of 7 and is neither acid nor
  base

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pH measures the relative amount of H ions in a
solution
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Neutralization

• To neutralize means to make the pH of a solution
  7
• Acids and bases can neutralize each other

• If the amounts are equal
• strong base strong acid neutral solution
• strong base weak acid weaker base solution
• weak base strong acid weaker acid solution

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Neutralization Reactions

• Acids and bases react to form water and salt
• Salt an ionic compound that is a product of a
  neutralization reaction between an acid and a
  base
• The base provides the OH- and the acid provides
  the H
• OH- H ? H2O
• The other ions from the acid and base form the
  salt
• EX. sodium hydroxide hydrochloric acid
• NaOH HCl ? NaCl H2O

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What is acid rain?

• Normal rain is slightly acidic, with a pH over
  5.7
• Acid rain rain with a pH below 5.5
• Acid rain can harm plants
• Acid rain can harm animals, particularly those
  that live in the water
• Acid rain can damage buildings and other
  structures

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How does acid rain form?

• Burning fossil fuels releases sulfur and nitrogen
  compounds into the atmosphere
• Sulfur dioxide reacts with moisture in clouds to
  produce sulfuric acid
• Nitrogen oxides react with moisture producing
  nitric acid
• The acids drop the pH of rainwater below 5.5
• The largest natural cause of acid rain is the
  release of sulfur dioxide by volcanoes

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Acids Bases - Main Idea

• Acids and bases react in water to form ions
• Acid and base solutions contain large amounts of
  positive or negative ions
• These solutions are highly reactive
• When mixed, acid and base solutions can
  neutralize one another
• pH scale measures the strength of an acid or base