Biology I What is pH?

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Biology IWhat is pH?
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Acids and Bases

• Some of our favorite foods make our tongue curl
  up because they are SOUR.

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Bitter!

• Some foods have a bite of their own because
  theyre somewhat bitter.
• WHY?

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Acidic/Basic

• There is a scientific reason for this
• These foods are either acidic or basic.
• The degree of acidity or alkalinity (basic) is
  important in organisms.

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Acids and Bases

• Chemicals may be classofied as acids or bases.
• Things that are neither acids nor bases are
  neutral.
• pH measures how acidic or basic a solution is.

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Acids

• Often taste sour
• Strong acids can burn skin eyes
• Strong acids can dissolve metals
• Examples
• Lemon juice
• Vinegar
• Car battery acid (dangerous!)

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Bases

• Can taste bitter, sweetish, or salty
• Strong bases can burn skin eyes
• Bases are often used for cleaning
• Examples
• Milk
• Baking soda
• Soap
• Drain cleaner (dangerous!)

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• Some substances are not really an acid or a base
  For example, pure water

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pH

• A special name is given to the acid or base
  characteristic that a substance has
• It is called pH
• p stands for potential and H stands for
  hydrogen hence, the potential of a substance to
  attract hydrogen ions

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Acid

• Any substance which has a pH of value of less
  than 7 is considered an acid
• Proton donors
• This means that the number of hydronium (H3O )
  ions is greater than the number of hydroxide ions
  (OH-).
• 0--------------7---------------14
• Acid Neutral Base

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Base

• Any substance which has pH value greater than 7
  is a base
• Proton acceptors
• This means that the number of hydroxide (OH-)
  ions in a solution is greater than the number of
  hydronium (H3O ) ions.
• 0--------------7---------------14
• Acid Neutral Base

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pH 7

• A pH of 7 is called neutralneither acid nor
  base.
• 0------------7------------14
• Acid Neutral Base

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The pH Scale

• Compares the relative concentration of H3O ions
  and OH- ions
• Scale ranges from 0 to 14 0-3 is very acidic 7
  is neutral 11-14 is very basic or alkaline
• Litmus paper, phenolphthalein, pH paper, other
  indicators that change color can be used to
  measure pH

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pH

• Using litmus paper An acid turns blue litmus
  paper red and a base turns red litmus paper blue.

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pH scale

• Scale for comparing the relative concentrations
  of hydronium ions and hydroxide ions in a
  solution
• Scale ranges from 0 to 14

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pH

• The lower the pH the stronger the acid
• The higher the pH the stronger the base
• pH 7.0 is neutral

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Buffers

• Control of pH is important to organisms
• Enzymes function only within a narrow pH range
  usually neutral
• Buffers neutralize acids or bases in organisms to
  help control pH