Transcript NOTES 10 – Acids, Bases, & pH Ion Review   An ion is an atom that gains or loses electrons giving it an.

NOTES 10 – Acids, Bases, & pH
Ion Review
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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 hydrogen’s electron can
become negative ions (more electrons than
protons)
 The leftover hydrogen proton becomes a
positive hydrogen ion
Water Molecules Form Ions
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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
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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
Dissociation of Water
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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
What are acids?
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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
Strong Vs. Weak Acids
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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+
Acids Are Useful But Can Be Dangerous
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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
What are bases?
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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
Strong Vs. Weak Bases
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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-
Bases Are Useful But Can Be Dangerous
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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
Acids, Bases, & Electricity
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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?
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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
What is pH?
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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
pH measures the
relative amount of H+
ions in a solution
Neutralization
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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
Neutralization Reactions
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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
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The other ions from the acid and base form the
salt
EX. sodium hydroxide + hydrochloric acid
NaOH + HCl  NaCl + H2O
What is acid rain?
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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
How does acid rain form?
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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
Acids & Bases - Main Idea
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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