Lactic acid makes your muscles hurt
Learning Target
• Classify acids, and bases on the basis of their properties; i.e.,
conductivity, pH, solubility, state
• Predict formulas and write names for common acids (e.g., sulfuric,
hydrochloric, nitric, ethanoic), using a periodic table, a table of ions,
and IUPAC rules
• We have classified compounds as ionic or molecular
• We can also classify compounds as acids or bases
What is an acid?
• In the mid 1800s, Swedish chemist Svante Arrhenius
proposed a theory of acids and bases.
• Both acids and bases are electrolytes, so they must
contain freely moving ions.
• One common feature of acids is that they all contain
hydrogen. Therefore, Arrhenius defined an acid as a
substance that reacts and releases hydrogen ions,
H+(aq), in a water solution.
Example: HCl(aq) (hydrochloric acid)
• One molecule of hydrogen chloride gas, HCl(g), forms the ions H+(aq)
and Cl-(aq) in water.
HCl(g)  H+(aq) + Cl-(aq)
• According to Arrhenius’s definition, hydrogen chloride dissolved in
water, HCl (aq) is acidic.
Common acids
What is a base?
• Arrhenius defined a base as a substance that dissolves in water and
releases hydroxide ions, OH-(aq), into the solution.
• Example: NaOH(s)  Na+(aq) + OH-(aq)
• Sodium hydroxide is an ionic compound that dissolves readily. It is a
basic substance because the hydroxide ion remains as a compound in
the solution (it does not break up into oxygen and hydrogen ions.)
Common bases
Coke cans in acid and base
• https://www.youtube.com/watch?v=WnPrtYUKke8
Indicators and pH
• Many acids and bases form
colorless solutions and look just
like water.
• Acid-base indicators change color
in response to the concentration
of hydrogen or hydroxide ions in a
solution.
• Example: Litmus paper turns red
in acids and blue in bases
Phenolphthalein is an indicator
• Phenolphthalein is a common
liquid indicator of acids and
bases. It is colorless in acids
but turns pink in bases
Alkaline is another way of saying basic
pH and pH scale
• To express the strength or weakness of an acidic or basic solution, chemists use
the pH scale
• pH is a number with no units that expresses the quantity of hydrogen ions, H+(aq),
in each litre of a solution
• The pH scale ranges from 0 to 14 and is used to express the hydrogen ion
concentration of a solution; a pH less than 7 indicates an acidic solution; a pH
more than 7 indicates a basic solution
Acids and bases are corrosive
Naming acids
Naming acids
• https://www.youtube.com/watch?v=a5nC2evhUa0 (7 min)