Introduction to Acids and

BasesKhady 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.

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

ACIDS

Common Acids

Vinegar (acetic or ethanoic acid)Citric 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 Hydroxide KOH

• 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+ + 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

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

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

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)