Acids and bases:Properties and definition

We encounter acids in our daily lives

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acetic acid(CH3CO2H)

citric acid(C6H8O7)

hydrochloric acid(HCl)

We encounter bases in our daily lives

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ammonia(NH3)

sodium hydroxide (NaOH)

An acid is a substance that produces H+ when dissolved in water

HX H+(aq) + X-

(aq) H2O

HCl H+(aq) + Cl-(aq)

H2O

Aqueous (or aq) is a solution wherein water is the solvent

Silberberg, M. 2010. Principles of General Chemistry. 2nd ed. New York: McGraw-Hill.

CH3CO2H H+(aq) + CH3CO2

-(aq)

H2O

The double-headed arrow signifies that the reaction goes forward and reverse

A base is a substance that produces OH- when dissolved in water

MOH M+(aq) + OH-

(aq) H2O

NaOH Na+(aq) + OH-

(aq) H2O

Brown, T., E. LeMay, and B. Bursten. 2000. Chemistry: The Central Science. 8th ed. Phils: Pearson Education Asia Pte. Ltd. Silberberg, M. 2010. Principles of General Chemistry. 2nd ed. New York: McGraw-

Hill.

NH3 NH4+

(aq) + OH-(aq)

H2O

The double-headed arrow signifies that the reaction goes forward and reverse

Acids and bases have the following properties

Acids

• taste sour

• aqueous acid conducts electricity

Bases

• taste bitter

• feel slippery

• aqueous base conducts electricity

Chang, R. 2002. Chemistry 7th ed. Singapore: McGraw-Hill.

Ions cause aqueous solutions to be good conductors

• to light the bulb, electric current must flow between the two wires

• ions carry electrical charge from one wire to another, thereby completing the circuit

copper wire

Acid-base reaction(aka neutralization reaction)

An acid-base reaction is a reaction between an acid and a base to form salt and water

acid + base salt + water

salt is an ionic compound made of a cation other than H+ and an anion other than OH- or O2-

HCl + NaOH NaCl + H2O

CH3CO2H + KOH KCH3CO2 + H2O

Chang, R. 2002. Chemistry 7th ed. Singapore: McGraw-Hill.

When vinegar reacts with baking soda, water and carbon dioxide are produced

CH3CO2H + NaHCO3 NaCH3CO2 + H2CO3

H2CO3 H2O + CO2

Acid-base indicators

An indicator is a substance that is added to a solution. It turns one color in an acidic medium

and turns another color in a basic medium

• litmus paper

• phenolphthalein

Brown, T., E. LeMay, and B. Bursten. 2000. Chemistry: The Central Science. 8th ed. Phils: Pearson Education Asia Pte. Ltd.

Litmus paper contains various organic compounds. It changes color depending on the

acidity/basicity of a solution

http://www.britannica.com/EBchecked/topic/343896/litmushttp://oldwww.mtlsd.org/senior/science/JPtachcinski/Lab_Proc/Basic%20Science%20Lab%20Techniques_files/litmus.jpe

red to blue: base

blue to red: acid

Phenolphthalein is colorless in acidic and neutral solutions but reddish pink in basic solutions

Chang, R. 2002. Chemistry 7th ed. Singapore: McGraw-Hill.Skoog, D., D. West, and F.J. Holler. 1996. Fundamentals of Analytical Chemistry 7th ed. USA: Saunders College Publishing.

C OH

CO

OH OH

C

C

OO

O

OOH

colorless reddish pink

pH

pH is a logarithmic scale that indicates the amount of H+ in solution

pH = - log [H+]

where [H+] = concentration of H+ in units of molarity

= moles H+ / L of solution

An HCl solution has [H+] = 1.00 x 10-6 M. Calculate for the pH of the solution

pH = - log [H+]

pH = - log [1.00 x 10-6]

= 6.00

pH values indicate if a solution is acidic, neutral, or basic

• If pH < 7.00, solution is acidic

• If pH = 7.00, solution is neutral

• If pH > 7.00, solution is basic

Schedule

• Feb 29– deadline for the submission of outline

• Mar 7 (4:30-6:00 pm)– LT # 3

• Mar 9-16– group reports

• Mar 21 (11:30-1:30, C-109)– finals

pH of some familiar aqueous solutions

Silberberg, M. 2010. Principles of General Chemistry. 2nd ed. New York: McGraw-Hill.

Acid rain

Silberberg, M. 2010. Principles of General Chemistry. 2nd ed. New York: McGraw-Hill.

The effect of industrial society on the environment is especially apparent in the problem of acid rain

major substances involved in acid rain

SO2 is converted to H2SO4

SO2 SO3

Silberberg, M. 2010. Principles of General Chemistry. 2nd ed. New York: McGraw-Hill.

oxidation

SO3 + H2O H2SO4

from power plant emissions

SO2 is converted to H2SO4

SO2 + H2O H2SO3

from coal

H2SO3 + H2O2 H2SO4 + H2O

air pollutant

Silberberg, M. 2010. Principles of General Chemistry. 2nd ed. New York: McGraw-Hill.

Nitrogen oxides (NOx) are converted to HNO3

N2 + O2 NOx

NOx N2O5

at night,

N2O5 + H2O HNO3

Silberberg, M. 2010. Principles of General Chemistry. 2nd ed. New York: McGraw-Hill.

NO is converted to NO2 and HNO3

NO NO2 + HNO3

Silberberg, M. 2010. Principles of General Chemistry. 2nd ed. New York: McGraw-Hill.

from combustion in car engines and

electric power plants

The pH of rain and snow has adversely declined in many parts of the world

• Much of the United States– as early as 1984, average rainfall pH = 4.2

• Sweden– rain with pH = 2.7 (about the same as

vinegar) has been observed

• West Virginia– rain with pH = 1.8 (between lemon juice and

stomach acid) has been observed

Silberberg, M. 2010. Principles of General Chemistry. 2nd ed. New York: McGraw-Hill.

Acid rain is harmful to marble buildings and sculptures

1908 1969

Chang, R. 2002. Chemistry 7th ed. Singapore: McGraw-Hill.

Acid rain is harmful to the ecosystem

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Honey, I told you not to leave your bike out in the rain!

Antacids

It is natural to have HCl in the stomach, but the problem occurs when the amount of HCl is too high

Chang, R. 2002. Chemistry 7th ed. Singapore: McGraw-Hill.

CO2 + H2O H2CO3

H2CO3 H+ + HCO3-

in the blood plasma,

by-product of metabolism

To temporarily reduce the amount of HCl in the stomach, an antacid may be taken. The HCl and

the antacid undergo an acid-base reaction

Kremil-S and Maalox contain Al(OH)3 and Mg(OH)2

3HCl +Al(OH)3 AlCl3 + 3H2O

2HCl +Mg(OH)2 MgCl2 + 2H2O

Chang, R. 2002. Chemistry 7th ed. Singapore: McGraw-Hill. Silberberg, M. 2010. Principles of General Chemistry. 2nd ed. New York: McGraw-Hill.

http://www.unilab.com.ph/hcp/CMS_Files/kremilStablet_productshot1.jpghttp://www.maaloxus.com/assets/productImages/regularLiquid.jpg

Acid inhibitors prevent the production of gastric acids by acting on acid-producing

cells in the lining of the stomach

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