pH
C h a p t e r 2 0

H
2
O ----> H + + OH -
Water splits apart into hydrogen ions (H+) and hydroxide ions (OH-).
This process is called self-ionization.

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 pH stands for potential hydrogen.
It is a measure of the hydrogen ion (H+) concentration in a solution.

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An acid is a substance that increases the Hydrogen ion (H+) concentration in a solution.
Acids taste sour.
Common acids include:
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Battery acid
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Stomach acid
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Lemon juice, tomatoes
Vinegar
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Beer, wine, soda, coffee
Rain
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Milk
Urine
Acids used in Chemistry
HCl Hydrochloric acid
HNO
3
Nitric acid
H
2
SO
4
H
3
PO
4
Sulfuric acid
Phosphoric acid
CH
3
COOH Ethanoic acid
H
2
CO
3
Carbonic acid

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A base is a substance that reduces the the H+ concentration in a solution. It has a lot of OH- ions.
Bases taste bitter and feel slippery.
Common bases include:
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Blood
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Seawater
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Pepto Bismal, Tums, etc.
Soap
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Ammonia
Bleach
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Oven Cleaner
Bases used in Chemistry
KOH Potassium hydroxide
NaOH Sodium hydroxide
Ca(OH)
2
Mg(OH)
2
Calcium hydroxide
Magnesium hydroxide

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If the concentration of hydrogen ions and hydroxide ions is equal, a solution is said to have a neutral pH.
Pure water (distilled water) has a neutral pH

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The pH scale ranges from 0-14.
Acids are less than 7, Bases are greater than 7.

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The numbers on the scale come from the H+ ion concentration, for example:
[H + ] = 10 -7  pH = 7
[H + ] = 10 -4  pH = 4
[H + ] = 10 -12  pH = 12 pH values are equal to the absolute value of the exponent of the H+ ion concentration.

The pH is the absolute value of 14 minus the absolute value of the [OH ] concentration
[OH ] = 10 -10  pH= 4
[OH ] = 10 -3  pH= 11
[OH ] = 10 -2  pH= 12

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Most biological fluids have pH 6 – 8
 pH values in human stomach can reach 2
Each pH unit represents a 10-fold difference in H + &
OH concentrations.
 small change in pH actually indicates a substantial change in [H + ] & [OH ]

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Buffers are substances that minimize changes in the concentrations of H+ and OH- in solution.
Buffers in your blood keep your pH close to 7.4 by accepting or donating H+ ions as needed.

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Titration: you add an indicator and watch for a color change pH meter: electronic, very sensitive pH paper (Litmus paper): color change scale
Cabbage Juice: natural pH indicator, color change

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Use the garbage cans!! Do the front side BEFORE you start your lab.
You will be testing 10 substances:
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1. isopropyl alcohol
2. vinegar
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3. baking soda solution
4. 7-up soda
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5. hydrogen peroxide
6. alka seltzer solution
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7. pineapple juice
8. bottled water
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9. tap water (get some from the faucet)
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10. your spit