Transcript Acids and Bases Chapter 6.3 & 6.4 Mini-Project Organize the following formulas into two groups with four formulas in each group: HNO3, NaOH, H2SO4, H2CO3,

Acids and Bases
Chapter 6.3 & 6.4
Mini-Project
Organize the following formulas into two
groups with four formulas in each group:
HNO3, NaOH, H2SO4, H2CO3, Ca(OH) 2, KOH,
H8PO4, Mg(OH) 2
One way to organize them into groups is:
Group One
Group Two
HNO3
NaOH
H2SO4
Ca(OH) 2
H2CO3
KOH
H8PO4
Mg(OH) 2
Group One formulas represent acids.
Group Two formulas represent bases.
ACIDS
• Taste sour (lemon, vinegar)
• React with metal (corrosion)
• React with carbonates (makes bubbles of
CO2
• Turns blue litmus RED
• In Water forms Hydrogen ION
HCl
Water
H+ + Cl-
BASES
•
•
•
•
•
Taste Bitter (soap, tonic water)
Feel Slippery (soap)
Turns Red Litmus Blue
In water, forms HYDROXIDE (OH-) ion
React with Acids to make water
NaOH
Water
Na+ + OH-
Indicators
• An Indicator is a chemical that turns colors
under certain conditions.
– Litmus paper is paper with the indicator litmus
on it.
– Litmus turns blue when in contact with a base
– Litmus turns red when in contact with an acid
– There are many different indicators
• Bromthymol blue, universal, malachite green, etc.
Why are Some Solutions Acid &
Others Base?
• Acid solutions contain more H+ ions than
OH- ions.
• Base solutions contain more OH- ions than
H+ ions.
• Water is the standard for Acid/Base and is
defined as NEUTRAL
• Water has equal amounts of H+ and OHions
Arrhenius Model of Acids/Bases
• Substance is an acid if it contains
hydrogen and dissociation causes
hydrogen ions to form in solution
• Substance is a base if it contains a
hydroxide and dissociates to produce
hydroxide ions in solution
Bronsted-Lowry Model
• Acid is a hydrogen ion donor
• Base is a hydrogen ion receptor
• This is a broader definition than Arrhenius
model because there are substances that
cause donation or reception without
having hydrogen in them.
Electrolytes
• Acids and Bases are ELECTROLYTES
– They ionize in water
– They conduct electricity
Strong vs. Weak
•Weak Acids/Bases vs.
Strong Acids/Bases
–Strong acids/bases
ionize completely
–Weak acids/bases only
partly ionize
•Strong Bases are just
as dangerous as Strong
Acids
–They react with most
things they touch
More
• Concentrated vs. Dilute
– Concentrated means lots of acid/base in a
little bit of water
– Dilute means a little bit of acid/base in a lot of
water
• Concentrated Acids and Bases are VERY
Dangerous
– They react quickly with many substances
Common Acids
Common Bases
Acid Rain
• Acid rain comes from rain collecting
gasses from the air to create acids:
– Carbon Dioxide = carbonic acid
– Sulfur oxides = sulfuric acid
– Nitrogen oxides = nitric acid
• Damages statues, buildings, kills forests,
kills fish
pH Scale
pH
• pH stands for ‘per hydrion’
–
–
–
–
–
–
It measures the amount of hydrogen ions in solution
Water is defined as ‘neutral’
Water has one H+ and one OH- equal numbers
The concentration of H+ in water is 1.0 x 10-7
The pH of water is 7
A lower pH means MORE Hydrogen ions (Acid)
• 10-6 is Larger than 10-7
– A higher pH means LESS hydrogen ions (Base)
• 10-8 is Smaller than 10-7
– pH scale is a way of showing this relationship of
hydrogen ions
pOH
• In water concentration of H+ =
concentration of OH– So [H+] = [OH-] = 1.0 x 10-7
– Think about it:
• H2O is the same as H-O-H which is H+ + OH-
• So pOH of water is also 7
• pH + pOH always equals 14, so
– pH scale goes from 1 to 14
Common Items on the pH Scale
Neutralization Reactions
Acid-Base Reactions
• Neutralization reaction is a reaction between an
acid and a base
– Makes Water + Salt
– Solution becomes Neutral (not acid or base)
– NOTE: salt is a ‘category’ of chemicals, not always
sodium chloride
HCl + NaOH
H2O + Na+ + Cl-
Acid-Base Reactions
• Mg(OH)2 + 2 HCl → MgCl2 + 2H2O
• Note:
– Cation from base (Mg) is combined with anion
from acid (Cl)
– The salt is MgCl2
– The H+ and OH- always combine to form
water
Acid-Base Titration
• Acid/Base Titration is the stoichiometry of
acid/base reactions.
– Titration is a method for determining the
concentration of a solution by using another
solution of known concentration
– Uses an INDICATOR to show when the
acid/base reaction is complete (neutral)
• Indicator is a chemical that changes color as
determined by acid or base conditions
• There are many indicators with different pH points.
Acid/Base Titration Curve
pH Indicators
pH Range of
Color Change
Name
Acid Color
Base Color
Methyl violet
Yellow
0.0 - 1.6
Blue
Thymol blue
Red
1.2 - 2.8
Yellow
Methyl orange
Red
3.2 - 4.4
Yellow
Bromocresol green
Yellow
3.8 - 5.4
Blue
Methyl red
Red
4.8 - 6.0
Yellow
Litmus
Red
5.0 - 8.0
Blue
Bromothymol blue
Yellow
6.0 - 7.6
Blue
Thymol blue
Yellow
8.0 - 9.6
Blue
Phenolphthalein
Colorless
8.2 - 10.0
Pink
Thymolphthalein
Colorless
9.4 - 10.6
Blue
Alizarin yellow R
Yellow
10.1 - 12.0
Red