ACIDS AND BASES

Acids properties

1. Conduct electricity (strong acids)

2. Change blue litmus to red

3. Have a sour taste

4. React with bases to neutralize their properties

5. React with active metals to liberate hydrogen

6. pH values 6-0

Acids

Acids are defined as: Substances which ionize to

form hydrogen(+) ions in aqueous solution. (Arrhenius)

Substances that act as proton donors (Bronsted-Lowry) or as electron-pair acceptors (Lewis)

Examples HCl, H2SO4

Bases properties

Base properties

1. Conduct electricity (strong bases)

2. Change red litmus to blue

3. Have a slippery feeling (like soap)

4. React with acids to neutralize their properties

5. pH values 8-14

Bases

Bases are defined as: Substances which ionize to form

hydroxide ions OH(-) in aqueous solution

Substances that act as proton receptors (Bronsted-Lowry) or as electron-pair donors (Lewis)

Examples: NH3OH, NaOH, CaCO3 , NaHCO3 (baking soda)

AMMONIAcleaner

pH Scale

The pH scale is used to measure how acidic or basic is a liquid.

pH measures the concentration of hydrogen ions (H+) and hydroxide ions (OH-).

The scale goes from 0 through 14. Distilled water is 7, so is called neutral.

lemon juice

0 1 2 3 4 5 6 7 8 9

10 11 12 13 14

pH Acidic

Neutral

Basic

vinegar

d water

baking soda

ammonia

detergent

Indicators

Indicator Acid Base

Red litmus paper Stays same Turns blue

Blue litmus paper Turns red Stays same

Bromophenol blue Yellow Stays blue

Phenolphtalein Colorless Pink

An indicator is a large organic molecule that works somewhat like a "color dye."

Natural indicators

There are natural indicators for acids and bases, and we may find them in our kitchen or garden! Red rose flowers Bougainvillea flowers Red cabbage Blue berries

http://tides.sfasu.edu:2006/cdm4/item_viewer.php?CISOROOT=/Digital&CISOPTR=1019&CISOBOX=1&REC=4

Acids and bases reactions

The acids react with bases, forming salts

ACID + BASE → SALT + WATER

HHCl + NaOHOH → NaCl + H2O

H-OH

Caves formation

Cave formation is based on a chemical

reaction between an acid and a base. This

acid is carbonic acid (H2CO3), and the base

is calcium carbonate (CaCO3), although it is

not a direct reaction.

Caves formation

Carbonic acid is formed by the reaction of rain water and carbon dioxide from soil. When the water is absorbed by the soil into the ground it reacts with the carbon dioxide present there:

H2O + CO2 → H2CO3

Water + carbon dioxide → carbonic acid

Carbonic acid is responsible for acid rain.

Caves formation

The acid water reacts chemically with rocks made of the base calcium carbonate, called limestone, and dissolves them:

H2CO3 + CaCO3 → Ca + H2CO3

Carbonic acid + calcium carbonate → calcium + carbonic acid

Caves formation

The calcium reacts with the hydrogen carbonate:

Ca + HCO3 → CO2 + CaCO3 + H2O

The carbon dioxide is given off into cave air to react again with rain water. Calcium carbonate is deposited, and water is formed. That’s the reason you will always see water inside the limestone caverns.

Caves formation

These series of chemical reactions are very slow and take thousands of years to produce the characteristic stalagmites and stalactites of these caverns.

http://tides.sfasu.edu:2006/cdm4/item_viewer.php?CISOROOT=/PPY&CISOPTR=81&CISOBOX=1&REC=1

Resources

Animation of cave formation on Exploring Earth:http://www.classzone.com/books/earth_science/terc/content/visualizations/es1405/es1405page01.cfm?chapter_no=visualization