I. Intro to Acids & Bases
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Transcript I. Intro to Acids & Bases
Ch. 23 - Acids & Bases
I. Intro to Acids & Bases
Definitions
Properties
Uses
A. Definitions
Acids
• Substances that donate hydrogen ions (H+)
form hydronium ions (H3O+) in water
HCl + H2O
+
H3O
+
–
Cl
Properties of Acids
sour
taste
corrosive
electrolytes
turn litmus red
react with metals to form H2 gas
Strength of acid depends on how well
they form H+ in water.
pH less than 7
Some examples of Acids
HNO3 + H2O H3O+ + NO3Nitric acid water hydronium ion nitrate ion
Some Examples of Acids
Digesting Your Food
Your stomach
contains two strong
acids: HCl
(hydrochloric acid
and pepsin).
More examples of Acids
H3PO4
- soft drinks, fertilizer, detergents
H2SO4
- fertilizer, car batteries
HCl
- gastric juice
HC2H3O2
- vinegar
Bases
A
base is a substance that either
contains hydroxide ions-OH-, or reacts
with water to form hydroxide ions.
NH3 + H2O
+
NH4
+
OH
Hydroxide
Properties of Bases
bitter
taste
corrosive
electrolytes
turn
litmus blue
slippery
pH
feel
greater than 7
Some examples of Bases
•KOH K+ + OH•potassium hydroxide -> potassium ion plus hydroxide
Many soaps contain
bases!
Some Common Bases & Uses
NaOH - lye, drain and oven cleaner, hair relaxers
Mg(OH)2 - laxative, antacid- “MOM” Milk of magnesia
NH3 - cleaners, fertilizer
Al(OH)3
aluminum hydroxide
Maalox (antacid)
Strengths of Acids and Bases
Strong
Acid/Base
• 100% ions in water
• strong electrolyte
• HCl, HNO3, NaOH, LiOH
Weak Acid/Base
• few ions in water
• weak electrolyte
• HC2H3O2, NH3
-
+
-
+
Concept Test!
Which
of the following "molecular"
pictures best represents a
concentrated solution of the weak
acid HA?
A.
B.
pH Scale- measuring the strength
of acids and bases
pH
• a measure of the concentration of
H3O+ ions in solution
• measured with a pH meter or an
indicator with a wide color range
14
0
7
INCREASING
ACIDITY
NEUTRAL
INCREASING
BASICITY
The pH scale is a way of
expressing the strength of acids
and bases. Instead of using very
small numbers, we just use the
NEGATIVE power of 10 on the
Molarity of the H+ (or OH-)
ion.
Under 7 = acid
7 = neutral
Over 7 = base
pH of Common Substances
0-3 strong acids 4-6 weak acids--8-11 weak bases 12-14 strong
bases
pH
pH
pH
pH
pH Testing
Indicator
• substance that changes color in an
acid or base
Examples:
• Litmus paper - red/blue
• phenolphthalein - colorless/pink
• goldenrod - yellow/red
• red cabbage juice (natural indicator)pink/green
Neutralization Reactions
When an acid and a base react, they produce a salt
and water.
Acid + Base salt + water
HCl + NaOH NaCl + H2O
The pH of the products will be nearly neutral or 7.0.
Neutralization to the rescue! When a strong acid is
spilled in the lab, it can be neutralized using a base –
like baking soda.
When a strong base is spilled, it can be neutralized
using an acid-like vinegar.
Both will produce salt-water with a pH of near 7.0.
A common neutralization
reaction!
People use antacids such as Tums or Rolaids
to neutralize stomach acid (HCl) from
overeating and drinking.
Antacids are weak bases. Baking soda and
water can also be used.
What do these weak antacids do to the excess
stomach acid?