Acids and Bases

They don’t blow up in your faces!

Acid Definition

• Acids are substances that contain an H+ ion. An H+ ion is a hydrogen atom with a positive electrical charge. The H+ is usually listed first in the chemical name of an acid. (HCl, H2SO4)

Acid Properties

• Acids are usually extremely corrosive. –They react with metals to form

hydrogen gas • Acids taste sour, tangy, hot and

fruity. • Acids conduct electricity

Acids in your house

• Most fruits have acids

–Citrus fruits are acidic from CITRIC ACID

• Soda that is carbonated is acidic

• Vinegar! (acetic acid)

Arrhenius Acids

• Acids dissociate (break into ion pieces) when they are dissolved in water.

• One of these pieces is always Hydrogen ion (H+ ).

• Dissociation of HCl HCl H+ + Cl-

Strong Acids

• Strong acids are strong electrolytes

• Strong acids dissociate completely into hydrogen ions and anions

• Weak acids do not conduct electricity as well because they do not dissociate completely into ions!

Hydronium ions

• Hydronium ions (H3O+ ) are just hydrogen (H+) ions attached to water

• H+ + H2O H3O+

• When hydrogen ions are in water, this happens!

Base Definition (1)

• Bases are substances that contain a hydroxide ion ( OH- ). The OH- is usually listed last in the chemical name of a base.

• Examples (NaOH, Ca(OH)2)

• There are some bases that need a better definition!

Arrhenius Base

• Bases form hydroxide ions when put into water.

• NH3 is a base because it makes NH4 + and OH– when it is added to H2O.

• Bases with OH in them (like NaOH) dissociate to form OH– .

Base Properties• Bases can be corrosive.

–They react well with organic things like skin!

• Bases are bland, slippery, slimy, or sticky.

If you get a base on your fingers, it will feel slippery. YOUR SKIN IS COMING OFF!

Base Properties

• Bases also conduct electricity. Do you know why?

Bases in your house

• SOAP – feels slimy, doesn’t it?

• Lots of cleaning things

–Ammonia

–Drano

Indicators

• Substances that respond to the H+ or OH- ions and show a different color depending on the pH.

• Most indicators have one color when they are in acid, and another in base.

• Each changes at a specific pH

The pH scale

• The pH scale shows how acidic a solution is.

• It goes from 0-14

• Acids have low pH

• Bases have high pH

• 7 is neutral, not acid or base

pH

• pH depends on the concentration of hydrogen ion in the solution–Lots of hydrogen ion = low pH–Very little hydrogen ion = high pH

• What things from home would you like to test?

More resources

• You should READ pp. 542-547 and 563-564

• Do these problems

–P. 549 # 1, 2, 4, 5