I. Intro to Acids & Bases

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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?

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