Transcript Acids, Bases, & Salts

Introduction to
Acids and Bases
Khady Guiro
NJIT C2PRISM Fellow
DO NOW
• Brainstorm
– What are common acids and bases?
– What tools can be used to measure
acids and bases?
Introduction
• Organisms are often very sensitive to the effect of
acids and bases in their environment.
• They need to maintain a stable internal pH in order
to survive—even in the event of environmental
changes.
• Many naturally occurring biological, geological, and
man-made chemicals are capable of stabilizing the
environment’s pH.
• This may allow organisms to better survive in
diverse environments found throughout the earth.
Introduction Cont.
• Acids and bases are a way of classifying
compounds based upon what happens to
them when you place them in water.
• An acid is a substance that yields an excess
of hydrogen ions when dissolved in water.
• A base is a substance that yields an excess
of hydroxide ions when dissolved in water.
OH 

Definitions of Acids and
Bases
 
• An acid is a substance that breaks into H
ions in an aqueous solution.

• A Base (is a substance that breaks into OH  
ions in an aqueous solution.
• Note: aqueous solution is any solution
where H 2 O is the solvent.
ACIDS
Common Acids
Citric Acid
Vinegar
(acetic or ethanoic
acid)
Characteristics of Acids
• Sour taste (for
edible acids)
• May burn your
skin
• Turn litmus paper
from blue to red.
Other Examples of Acids
• HCl
Hydrochloric Acid
• H2SO4
Sulfuric Acid
• CH3COOH Acetic Acid (Vinegar)
BASES
Common Bases
Ammonia
Characteristics of Bases
• Bitter taste (for edible
bases only)
• Can be poisonous and
corrosive.
• Feels slippery
• Turn litmus from red
to blue.
Other examples of Bases
• Sodium Hydroxide
NaOH
• Potassium HydroxideKOH
• Ammonia
NH3
Three Definitions of Acids
and Bases
Three Definitions of Acids and
Bases
• Svante Arrhenius (Swedish 1887)
• Bronsted- Lowry (Danish and
English 1923 independently
proposed definition)
• Gilbert Lewis (American 1920’s)
Arrhenius Definition of Acids
and Bases
• Acids produce hydrogen ions (H+) in
an aqueous solution, while bases
produce hydroxide ion (OH-).
Acid:
HCl (aq) H+ (aq) + Cl- (aq)
Base: NaOH(aq) Na+(aq) + OH-(aq)
Bronsted- Lowry Definition
of Acids and Bases
• An acid is a proton (H+) donor.
• A base is a proton (H+) acceptor.
• Example:
HF + H2O H3O+ + FAcid
Base
H3O+ : hydronium ion
Lewis Definition of Acids and
Bases
• An acid accepts a pair of electrons.
• A base donates a pair of electrons.
• This is a more general definition than
the previous two.
• Example:
:NH3 + H+  NH4+
Three Models of Acids and
Bases
Model
Definition of
Acid
Definition of
Base
Arrhenius
H+ producer
OH- producer
Bronsted-Lowry H+ donor
H+ acceptor
Lewis
Electron-pair
donor
Electron-pair
acceptor
Conjugate Acids and Bases
• Conjugate acid is the particle
formed that has received the proton.
(ex: H3O+)
• Conjugate base is the particle left
from the acid once it has donated
the proton.
Conjugate Acids and Bases
• General expression:
HA (aq) + H2O (l) H3O+ (aq) + A- (aq)
Acid
Base
Conjugate
Acid
Conjugate
Base
Importance of WATER
• Water acts as an acid and as a
base. It is amphoteric
Acids
• A dilute acid has lots of water and a
small amount of acid
• A concentrated acid has lots of acid
and not much water so must be
handled carefully
• A strong acid releases lots of H+
• A weak acid releases fewer H+
The extent to which a
compound is acidic or
basic is measured by the
pH scale.
Measuring acid strength?
• To decide if something is an acid or a base we
can use an indicator.
• Litmus and Universal Indicator are examples
of indicators.
• They change colour depending on if they are in
an acid or a base.
What is the pH scale?
• The pH scale
measures
how acidic
or basic a
solution is.
Identifying Acids and
Bases
• Acids have a ph from 0-7
• Lower pH value indicates a
stronger acid.
• Bases have a pH from 7-14
• Higher pH value indicates a
stronger base.
Did we Miss something??
• What happens when the pH of a
substance is 7?
• Ans: A pH level of 7 indicates a
Neutral Substance i.e: Water!
Why Learn about Acids &
Bases?
• What do you think is the pH level of
NYC tap water?
• The pH of a swimming pool must be
checked periodically. Why?
• Is it important for Lakes & Rivers to
maintain a certain pH?
Situations in which pH is
controlled
•
•
•
•
•
“Heartburn”
Planting vegetables and flowers
Fish Tanks and Ponds
Blood
Swimming pools
Acid Rain
• Pollution in the air (sulfur dioxide,
carbon dioxide, nitrogen dioxide)
combines with water to form various
acids.
.
pH in the Digestive System
• Mouth-pH around 7. Saliva contains
amylase, an enzyme which begins to break
carbohydrates into sugars.
• Stomach- pH around 2. Proteins are broken
down into amino acids by the enzyme
pepsin.
• Small intestine-pH around 8. Most
digestion ends. Small molecules move to
bloodstream toward cells that use them
Review
Acids
þ Produce H+ (as H3O+) ions in water
þ Produce a negative ion (-) too
þ Taste sour
þ Corrode metals
þ React with bases to form salts and water
Bases
Produce OH- ions in water
Taste bitter, chalky
Are electrolytes
Feel soapy, slippery
React with acids to form salts and
water
pH of Common Substances
Timberlake, Chemistry 7th Edition, page 335
Buffers
• A buffer is a solution that resists
changes in pH when small amounts
of acids and bases are added.
Vernier experiment
Today’s Experiment
• Using Vernier Software:
– Calibrate pH sensor using Buffers
– Test the pH of distilled water, HCL,
NAOH.
– Test pH of 5 Unknowns
– Test pH of common house hold items
(Ketchup, coffee, tap water, Detergent)