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Ionization of Water. Water molecules have a tendency to “fall apart” or dissociate “Dissociate” means to separate or disconnect from. Two water molecules. Ionization of Water. This is usually written in a simplified version. Ionization of Water.

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ionization of water
Ionization of Water
  • Water molecules have a tendency to “fall apart” or dissociate
  • “Dissociate” means to separate or disconnect from

Two water


ionization of water1
Ionization of Water
  • This is usually written in a simplified version
ionization of water2
Ionization of Water
  • This is usually written in a simplified chemical equation:

H2O  OH- + H+

one water






ionization of water3
Ionization of Water

How often does water disassociate to form ions?

In pure water, about one water molecule in 550 million naturally dissociatesinto a Hydrogen Ion(H+)and a Hydroxide Ion(OH-)

ionization of water4
Ionization of Water

Because the number of positive hydrogen ions(H+)is equal to the number of negative hydroxide ions(OH-) produced, water is neutral.

pop quiz
Pop Quiz

What is an ion?

A polar molecule

An atom with which gained or lost protons

An atom with a + or – charge

A molecule that loses an atom

ionization of water5
Ionization of Water

Onewater molecule in 550 million naturally dissociatesinto a Hydrogen Ion (H+) and a Hydroxide Ion(OH-)

Hydrogen Hydroxide

Ion Ion

H2O  H+ + OH-

ph scale
pH scale
  • Chemists created a measurement system called the pH scale to indicate the concentration of H+ ions in solution.
  • The pH scale measures the concentration of H+ ions in a solution. The scale ranges from 0 to 14.
  • Each unit is a 10x change in concentration
  • At pH 7, the concentration of H+ ions and OH- ions is equal. Thus, pH 7 is neutral.
  • Solutions with a pH below 7 are called acidic because they have more H+ ions than OH- ions.
  • Examples include lemon juice, stomach acid, aspirin, and coffee.
  • StrongAcids have a pH of 1-3
  • Strong acids producelots of H+ ions
  • Solutions with a pH above 7 are called basic because they have more OH- ions than H+ ions.
  • Examples include soap, bleach, and seawater
  • Strong Bases have a pH of 11 to 14
  • Containlots of OH-ions and fewer H+ ions
the ph scale review
The pH Scale Review
  • Indicates the concentration of H+ ions
  • Ranges from 0 – 14
  • pH of 7 is neutral
  • pH0 up to 7 is acid … H+
  • pHabove 7 – 14 is basic… OH-
  • Each pH unit represents a factor of 10X change in concentration
  • pH 3 is 10 x 10 x 10 (1000) stronger than a pH of 6
A substance that eliminates large sudden changes in pH.

Buffers help organisms maintain the pH of body fluids within the narrow range necessary for life.

Are combinations of H+ acceptors and donors forms in a solution of weak acids or bases

Work by accepting H+ from solutions when they are in excess and by donating H+ when they have been depleted.


Why do we care about pH?

  • Living organisms are sensitive to pH levels and an imbalance in pH can lead to DEATH!
  • Organisms have developed ways of keeping pH within normal ranges using an acid-base buffering system
  • Buffer = substances that minimized change in pH

Biological pH

  • The pH of our stomachs are around 1-2, so that foods can be broken down
  • The optimal pH for healthy skin and scalp is around 5 slightly acidic for resistance to infection and diseases
  • Soaps and shampoos are basic and thus can cause drying of the skin and scalp
  • When you see a “pH-balanced” shampoo or soap, the manufacturer has lowered the pH so its closer to normal skin pH
  • Most organisms have an internal pH of
acid precipitation
Acid Precipitation
  • Rain, snow or fog with more strongly acidic than pH of 5.6
  • West Virginia has recorded 1.5 pH
  • East Tennessee reported 4.2 in 2000
  • Occurs when sulfur oxides and nitrogen oxides react with water in the atmosphere
    • Lowers pH of soil which affects mineral solubility – decline of forests
    • Lower pH of lakes and ponds – In the Western Adirondack Mountains, there are lakes with a pH <5 that have no fish.