properties of acids and bases get 8 test tubes. rinse all tubes well with water. add acid to four...
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Properties of acids and basesProperties of acids and bases• Get 8 test tubes. Rinse all tubes well with water. Add
acid to four tubes, base to the other four.• Touch a drop of base to your finger. Record the feel
in the chart (on the next slide). Wash your hands with water. Repeat for acid.
• Use a stirring rod, add base to the litmus and pH papers (for pH paper use a colour key to find a number). Record results. Repeat for acid.
• Into the four base tubes add: a) two drops of phenolphthalein, b) 2 drops of bromothymol, c) a piece of Mg, d) a small scoop of baking soda. Record results. Repeat for acid.
• Clean up (wash tubes, pH/litmus paper in trash).
Baking soda
Magnesium
Bromothymol
Phenolphthalein
Litmus (blue or red)
pH (# from the key)
Feel (choose slippery or not slippery)
SourBitterTaste
HCl(aq)NaOH(aq)ObservationsObservations
BubblesNRBaking soda
BubblesNRMagnesium
*Yellow*BlueBromothymol
*Cloudy/ white
*PinkPhenolphthalein
RedBlueLitmus (blue or red)
114pH (# from the key)
Not slipperySlipperyFeel (choose slippery
or not slippery)
SourBitterTaste
HCl(aq)NaOH(aq)ObservationsObservations
*Usually, but not always
Historical views on acidsHistorical views on acids
• The more recent Bronsted-Lowry concept is that acids are H+ (proton) donors and bases are proton acceptors
Ionization
+Cl HH
HO
+H
HH O Cl+
• O (e.g. H2SO4) was originally thought to cause acidic properties. Later, H was implicated, but it was still not clear why CH4 was neutral.
• Arrhenius made the revolutionary suggestion that some solutions contain ions & that acids produce H3O+ (hydronium) ions in solution.
Bronsted-Lowry theory
• An acid is a substance from which a proton (H+ ion) can be removed
• A base is a substance that can remove a proton (H+ ion) from an acid
• An acid-base reaction involves the transfer of a proton
Types of Acids
• Acids may have more than one proton to donate.– Monoprotic acids contain 1 hydrogen ion i.e.
HCl(aq)
– Diprotic acids contain 2 hydrogen ions, i.e. H2SO4(aq)
– Triprotic acids contain 3 hydrogen ions, i.e. H3PO4(aq)
Conjugate acid-base pair
Two molecules or ions that are related by the transfer of a proton (H+) are called a conjugate acid-base pair.
(conjugate means “linked”)
The Bronsted-Lowry conceptThe Bronsted-Lowry concept• In this idea, the ionization of an acid by water
is just one example of an acid-base reaction.
• Acids and bases are identified based on whether they donate or accept H+.
• “Conjugate” acids and bases are found on the products side of the equation. A conjugate base is the same as the starting acid minus H+.
+Cl HH
HO
+H
HH O Cl+
acid base conjugate acid conjugate base
conjugate acid-base pairs
Example:HBr(aq) + H20(l) -> H30+(aq) + Br-
(aq)
Conjugate base of an acid is the particle that remains when a proton is removed from the acid (in this example: Br-(aq)
Conjugate acid of a base is the particle that results when the base receives the proton from the acid (in this example: H30+(aq)
Practice problemsPractice problemsIdentify the acid, base, conjugate acid, conjugate base, and conjugate acid-base pairs:
acid base conjugate acidconjugate baseHC2H3O2(aq) + H2O(l) C2H3O2
–(aq) + H3O+(aq)
conjugate acid-base pairs
acidbase conjugate acidconjugate baseOH
–(aq) + HCO3–(aq) CO3
2–(aq) + H2O(l)
conjugate acid-base pairs
Acids
An acid is a substance that produces Hydrogen ions, H+(aq) in water (Arrhenius definition).
The hydrogen ion (H+) bonds with a water molecule to make a hydronium ion, H30+ (aq) (H+ -> H20 = H3O+)
Strong acids
A strong acid is an acid, which ionizes extremely well. Essentially all of the acid molecules are ionized. (lots of H3O+)
Example: HCl, HBr, HNO3, H2SO4, HClO4
Example:HCl (aq) + H2O(l) -> H30+(aq) + Cl-(aq)
H2SO4(aq) +2H2O(l) -> 2H3O+ + SO42-(aq)
(Ionization equations show how they react with water to make H3O+)
Weak acid
A weak acid is an acid which ionizes poorly. Only a small percentage of the acid molecules actually ionize. (a few H3O+)
Example: HC2H3O2
HC2H3O2(aq) + H2O(l) H3O+(aq) + C2H302-
Avoid confusing terms!
• Concentrated/Dilute vs Strong/Weak
• A strong acid such as HCl can be concentrated (12mol/L) or dilute (0.5mol/L)
• Concentrated or dilute refers to the amount of solute dissolved in the solvent
• Strong or weak- refers to the degree of dissociation of ions in solutions.
Bases
A base is a substance that produces hydroxide ions, OH-, in water (Arrhenius defintion)
A strong base is a base that dissociates 100% in aqueous solution.
Example: NaOH(s) Na+(aq) + OH-(aq)KOH(s) -> K+(aq) + OH-(aq)(Ionization equations: show how they make ions)