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Chemistry Notes: Acids and BasesChemistry 2014-2015
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
Aqua regia is a concentrated mixture of hydrochloric and nitric acid. It creates toxic fumes of chlorine gas and is capable of dissolving gold. It is represented by a fire-breathing dragon in old alchemy works.
Trivia: Aqua Regia
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
Well, what is H2SO4? Why is Johnny no more?
Acids generally begin with H, so their formulas are easy to recognize. The name of an acid depends on everything after the H in the formula (the anion).
Writing Names and Formulas for Acids and Bases—Acids
Common acids HCl hydrochloric
acid HNO3 nitric acid
H2SO4 sulfuric acid
H3PO4 phosphoric acid
HC2H3O2 acetic acid
H2CO3 carbonic acid
Determine the name of the anion in the acid. For example, HI contains iodide, I-. H2SO3 contains sulfite, SO3
2-. H2Cr2O7 contains dichromate, Cr2O72-.
The last three letters of the anion determine the rules you will use to name the acid. You will take the root of the acid’s name from the anion it contains. -ide hydro ________ ic acid -ite ____________ ous acid (no prefix) -ate ___________ ic acid (no prefix)
Writing Names and Formulas for Acids and Bases—Acids
Therefore, HI is hydroiodic acid, H2SO3 is sulfurous acid, and H2Cr2O7 is dichromic acid. Note that acid names do not contain the word “hydrogen”. To determine the name of an acid from its
formula, you need to swap and drop the anion with hydrogen ions. For example, nitric acid must contain nitrate, NO3
-. If you swap and drop hydrogen (H+) with NO3
-, you get HNO3.
Writing Names and Formulas for Acids and Bases—Acids
Bases are relatively easy to name, since many contain the hydroxide ion, OH-. Ex. Ba(OH)2 is barium hydroxide, NaOH is sodium hydroxide, Al(OH)3 is aluminum hydroxide, Fe(OH)2 is iron (II) hyroxide.
One exception to the rule above is the weak base NH3, ammonia.
Except for ammonia (NH3, a formula you “just need to know”), you usually need to swap and drop to determine the formula of a base. Most will contain hydroxide.
Writing Names and Formulas for Acids and Bases—Bases
Write the names for the following acids and bases.
LiOH H2SO4 NH3
Names and Formulas Practice
Write the names for the following acids and bases.
Mg(OH)2 HNO2 HCN
Names and Formulas Practice
Write the names for the following acids and bases.
HBr Sr(OH)2 HClO4
Names and Formulas Practice
Write the formulas for the following acids and bases.
Ammonia Nitric acid Hydrochloric acid
Write the formulas for the following acids and bases.
Calcium hydroxide Chromic acid Chlorous acid