introduction to acids and bases khady guiro njit c 2 prism fellow
TRANSCRIPT
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.
Definitions of Acids and Bases
• An acid is a substance that breaks into ions in an aqueous solution.
• A Base (is a substance that breaks into ions in an aqueous solution.
• Note: aqueous solution is any solution where is the solvent.
H
OH
OH
OH 2
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)
Characteristics of Bases
• Bitter taste (for edible bases only)
• Can be poisonous and corrosive.
• Feels slippery• Turn litmus from red
to blue.
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+ + F-
Acid 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 acceptor
Electron-pair donor
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 Conjugate
Acid Base
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+
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.
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
Acids
þProduce H+ (as H3O+) ions in water
þProduce a negative ion (-) too
þTaste sour
þCorrode metals
þReact 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
Buffers
• A buffer is a solution that resists changes in pH when small amounts of acids and bases are added.