chemistry notes: acids and bases. properties of acids and bases acids taste sour (vinegar, lemons) ...
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Chemistry Notes: Acids and Bases
Properties of Acids and Bases
Acids taste sour (vinegar,
lemons) aqueous solutions of acids
are electrolytes cause indicators to change
colors many metals react with
acids to produce H2 gas react with bases to form a
salt and water most formulas begin with
H
Bases bitter taste (soap,
unsweetened chocolate) bases are electrolytes in
aqueous solution cause indicators to
change colors feel slippery react with acids to form a
salt and water often contain OH- , or
ammonia NH3
ExamplesThe bolded formulas below to STRONG acids and
bases
Common acids HCl HNO3
H2SO4
H3PO4
HC2H3O2
H2CO3
Common bases NaOH KOH Ca(OH)2
LiOH NH3
The pH of a substance can tell us if it’s an acid, a base, or neutral. pH is a measurement of the concentration of hydrogen ions (H+) in a solution. The more hydrogen ions present, the more acidic a substance is.
Acids have large amounts of hydrogen ions, and low pH (pH < 7).
Bases have small amounts of hydrogen ions, and high pH (pH > 7).
Measuring pH
Another measurement, pOH, tells use the concentration of hydroxide (OH-) ions in a solution. The more hydroxide ions present, the more basic a substance is.
Acids have small amounts of hydroxide ions, and high pOH (pOH > 7).
Bases have large amounts of hydroxide ions, and low pOH (pOH < 7).
Neutral substances have equal amounts of hydrogen and hydrogen ions (pH = 7, pOH = 7).
The pH and pOH of a substance always add up to 14.
pH = 5.6 NH3
Large concentration of OH- ions Small concentration of H+ ions
pOH = 3.2 pH = pOH H2SO4 NaOH
Large concentration of H+ ions HCl
Practice: Are these solutions acidic, basic, or neutral?
If the pH of a solution is 6, what is its pOH? Is it an acid or base?
If the pH of a solution is 4, what is its pOH? Is it an acid or base?
If the pOH of a solution is 3, what is its pH? Is it an acid or base?
Practice: Are these solutions acidic, basic, or neutral?
Indicators are substances that change color in solutions of different pH
Help determine approximate pH
Indicators
Colorless in acid
Pink in base
Phenolphthalein
Mixture of indicators Changes into
different colors at each pH (rainbow)
Red/orange in acid, blue/purple in base, green around pH = 7
Universal indicator
Blue litmus turns red in acid
Red litmus turns blue in base
Litmus paper