May 15, 2012
1. Pick up your paper. 2. Turn your homework into the tray.
YOU NEED YOUR BOOK!
Hom
ewor
k
Answer 3 and 4 on a separate sheet of paper.
You might want to go back and review the procedure.
Using chapter 8 vocab, explain why you weren't able
to dissolve all of the rock salt. Was your procedure
valid? Why or why not?
Agenda
1. Pre­test
2. Acids, Bases notes
3. Venn Diagram
4. Homework May 15­8:31 AM
What is pH?
1. Scale (powers of 10) based on concentration of H3O+ ions in a solution. Also indicates the concentration of hydroxide ions, OH­ ACIDIC is O ­ 6
BASIC is 8 ­14
NEUTRAL is 7
Low pH means high H+ ions.
Question: What are Acids?
Answer: an acid is any substance that produces hydronium ions (H3O+) when dissolved in water
Question: What is a Hydronium Ion? Answer: when an acid is dissolved in water it separates or IONIZES into H+ ions, these H+ ions immediately attach themselves to a polar water molecule to become H3O+
For Example: HCl is an acid
When it dissolves in water, the H+ ions separate for the Cl‐ ions
The H+ ions attach themselves to the polar water molecules to form H3O and Cl‐ ions are left over
HCl is therefore an ACID because it transfers H3O Ions
Properties of Acids
Acids­ chemicals that release H3O+ (hydrodium) in a solution.
So...acids produce more H+ ions (lower pH).
Properties
1. Low pH ­­ 0 = most acidic
2. Sour taste
3. Cause indicators to change color (Ex. turns litmus red)
4. Conducts electrical current
5. Reacts with metals (corrisive)
6. Electrolytes
Question: What are bases?
Answer: any substance that produces (OH‐) or Hydroxide Ions when dissolved in water
(you use bases everyday (Soap) is a base)
Sodium Hydroxide is a Base‐‐found in many household drain cleaners
This compound ionizes in water to form Na+ and Hydroxide Ions
NaOH ‐‐> Na+(aq) + OH‐(aq)
Another Example is Ammonia
NH3 + H20 ‐‐> NH4 + OH‐
The ammonia Ion accepts a H+
May 15­9:32 AM
Properties of Bases
Bases­ chemicals that release hydroxide ions, OH­, in a solution. So...bases produce more OH­ ions and less H+ ions (high pH). Properties
1. High pH ­­ 14 = basic
2. Bitter taste
3. Feels slippery
4. Causes indicators to change color (Ex. turns litmus paper blue)
5. Corrosive
6. Reacts with skin
pH
1. How do these pH values compare?
• pH < 7 means [H+] > [OH­]
• pH > 7 means [H+] > [OH­]
• pH = 7 means [H+] = [OH­]
pH
2. Why is pH important?
• pH of drinking water indicates its quality.
­­ pH too high, pipes corrode
­­ pH too low, pipes corrode
• pH important to life
­­ pH of natural bodies of water has to be right (pH 6­8) for fish and other aquatic animals and plants to reproduce. ­­ lower and they die!
• pH play an important role in digestion
Uses
• Acids (low pH) used throughout industry...
fertilizers, soft drinks, batteries, etching metals and glass
• Bases (high pH) unclog drains: used as cleaners, soaps, shampoos
Strong vs. Weak
• Strong acids and bases dissociate (break apart into ions) almost completely in water. • Weak acids and bases dissociate (ionize) incompletely in water. • Concentrated­ little water in the solution and LOTS of acid/base molecules.
• Dilute­ lots of water in the solution and FEW acid/base molecules.
Strong vs. Weak Acids
Acids are classified according to the degree to which they produce H3O ions when dissolved in water
HCl is a very strong ACID!
It is so strong because when put in water no HCl molecules will remain they all become H3O and Cl‐ ions
The Higher the Number of Hydronium Ions the Stronger the Acid
Acetic Acid on the other hand is a WEAK ACID! HC2H3O2 or Vinegar Only a few molecules of HC2H3O2 ionize in water thus it is a Weak Acid
The Lower the Number of Hydronium Ions the Weaker the Acid
Strong vs. Weak Bases
strength of a base depends on the relative amount of OH‐ ions produced, when the base is mixed with water
For example:
• Sodium Hydroxide is a strong base because it ionizes completely to form Na+ and OH‐ • Ammonia is a weak base because most of its molecules do not react with water to form NH4+ and OH‐
What happens when you mix an acid and a base?
• Mixing equal parts of an acid and base together, results in a solution made of salts. +
It is neutral (pH = 7, [H ] = [OH­])
They cancel each other.
Examples:
1. HCl + NaOH ­­> NaCl + H2O
2. H2SO4 + 2KOH ­­> K2SO4 + 2H2O
strong acid + strong base = salt + water
All acids and bases are neutral because they form ions when dissolved. Electrolytes
• Electrolytes ­­ ions which allow a solution to conduct electricity when dissolved in water. • Non­electrolytes­­ Chemicals that do not form ions when they are dissolved in a solution. Example: sugar in water
What is Acid Rain?
• Any rain, snow, hail, sleet, fog with a pH less than 5. • Harmful to plants, animals, people and buildings.
SOx and NOx (sox and nox)
Acid rain results from gases produced during pollution. ­­ SO2 from burning fossil fuels
­­ SO3 and NO2 from reactions with oxygen­containing compounds in the atmosphere.
­­ NO from coal and electrical power generation
• These sulfur and nitrogen gases mix with water to form sulfuric and nitric acids. SO3 + H2O ­­> H2SO4
air pollutant + rain ­­> acid rain