Salts Are Ionic Compounds of Metal-Nonmetal Composition
15,16-1
CHAPTER 15 & 16
(Acids & Bases)
Acids are substances which generally have a hydrogen in the front of their formula
Bases (alkaline) are substances which generally have a hydrogen in the back of their formula
Salts are ionic compounds of metal-nonmetal composition.
A binary acid is an acid that contains only two different elements: hydrogen and one of the more electronegative elements.
Ex: HCl - hydrochloric acid
An oxyacid is an acid that is a compound of hydrogen, oxygen, and a third element, usually a nonmetal.
Ex: HNO3 - nitric acid
15,16-2
Some Properties of acids:
- Aqueous solutions of acids have a sour taste.
[never use the "taste test" to find out]
Ex: lemons, oranges
2. Acids change the color of acid-base indicators.
*Ex: Turns blue litmus red
Phenolphthalein is colorless in acids
Bromothymol blue is yellow in acids
3. Some acids react with active metals to release hydrogen gas.
Ex: Zn (s) + H2SO4 (aq) --> ZnSO4 (aq) + H2 (g)
4. Acids react with bases to produce salts and water.
Ex: HCl + NaOH --> NaCl + H2O
acid base salt water
6. Some acids conduct electric current
15,16-3
Some Properties of bases (alkaline):
1. Aqueous solutions of bases taste bitter.
[never use the "taste test" to find out]
Ex: soap suds or limewater
- Bases change the color of acid-base indicators.
Ex: turns red litmus blue
phenolphthalein turns red
bromothymol blue is blue in a base
- Dilute aqueuos solution of bases feel slippery.
Ex: soap
- Bases react with acids to produce salt and water.
Ex: HCl + NaOH --> NaCl + H2O
acid base salt water
5. Bases conduct electric current.
15,16-4
Industrial acids
Sulfuric acid is manufactured in the United States more than any other chemical. Approximately 35 million tons each year.
Uses: -to make phosphoric acid
-production of cellulose products
-refining petroleum.
Nitric acid and phosphoric acid are and essential part of fertilizer production
Hydrochloric acid is the most expensive and most widely used as a lab reagent
Nearly all fruits contain acids15,16-5
- Lemons, oranges, and grape fruits contain citric acid.
- Apples contain malic acid
- The souring of milk produces lactic acid
- Vinegar is acetic acid
- The secretion in the human stomach is about 0.4% hydrochloric acid
Several substances long known as bases are commonly found in homes.
- Ammonia and ammonia solutions are familiar cleaning agents
- Lye is a commercial grade of sodium hydroxide-used for cleaning clogged sink drains
- Milk of magnesia is a suspension of magnesium hydroxide in water
- Soap is a base
- Tums and Rolaids are both bases
15,16-6
According to Arrhenius
Acids are chemical compounds that increase the concentration of hydrogen ions in aqueous solution.
Ex: HCl when dissolved in water H+aq +Cl-aq
Bases are substances that increase the concentration of hydroxide ions in aqueous solution.
Ex: NaOH (aq) --> Na+ (aq) + OH- (aq)
Ca(OH)2 (aq) --> Ca++ (aq) + OH- (aq)
According to Bronsted-Lowry
An acids is a molecule or ion that is a proton donor.
Ex: NH3 + H2O <--> NH4+ + OH-
in the above reaction water is considered an acid
A Bases is a molecule or ion that is a proton acceptor
Ex: HCl + H2O --> H3O+ + Cl-
in the above reaction water is considered a base
15,16-7
According to Lewis:
An acid is an atom, ion, or molecule that accepts an electron pair to form a covalent bond.
A base is an atom, ion, or molecule that donates an electron pair to form a covalent bond.
A conjugate base is the species that remains after an acid has given up a proton
A conjugate acid is the species formed when a base gains on a proton
Example:
HSO4- + H2O --> H3O+ + SO4--
| | | |
acid base conjugate acid conjugate base
H3O+ + SO4-- --> HSO4- + H2O
| | | |
acid base conjugate acid conjugate base
- In the above example, HSO4- and SO4-- are a conjugate acid-base pair
- In the above example, H3O+ and H2O are a conjugate acid-base pair
15,16-8
Fill in the appropriate acid or conjugate base
AcidConjugate Base
HCl______
HNO3______
NH4+______
H2SO4______
______SO4--
______F-
______C2H3O2-
______NH3
Any species than can react as either an acid or a base is described as amphoteric.
Ex: HCl + H2O --> H3O+ + Cl-[water is a base]
NH3 + H2O --> NH4+ + OH-[water is an acid]
Neutralization is the reaction of hydronium ions and hydroxide ions to form water molecules.
Ex: HCl + NaOH --> NaCl + H2O
acid base salt water
15,16-9
A salt is an ionic compound composed of a cation from a base and an anion from an acid.
Ex: HCl + NaOH --> NaCl + H2O
acid base salt water
In the self-ionization of water, two water molecules produce a hydronium ion and a hydroxide ion by transfer of a proton.
Hydronium Hydroxide
ion ion
For water at 25 degree C:
[H3O+] = 10-7 mole/L[OH-] = 10-7 mole/L
or [H3O+] = [OH-] = 10-7 mole/L
If the H3O+ ion concentration in a solution exceeds 10-7 mole/L, then the solution is acidic
Ex: A soln containing 10-5 mole H3O+ ion
per liter of soln is acidic
15,16-10
If the OH- ion concentration exceeds 10-7 mole/L, then the solution is basic
Ex: A soln containing 10-4 mole OH- ion per liter of soln is basic
The product of [H3O+] and [OH-] remains constant in water:
[H3O+] x [OH-] = constant
10-7 mole/L x 10-7 mole/L = 10-14 mole2/L2
[H3O+] x [OH-] = 10-14 mole2/L2
This means that if the concentration of one is known then the other can be calculated
Ex: A solution of NaOH has a concentration of 0.01-M. Calculate the concentration of [H3O+].
15,16-11
The pH of a solution is defined as the negative of the common logarithm of the hydronium ion concentration or more simply:
pH = - log [H3O+]
The pOH of a solution is defined as the negative of the common logarithm of the hydroxide ion concentration or more simply:
pH = - log [OH-]
Ex: Pure water is slightly ionized, and at 25oC contains 0.0000001 moles of H3O+ per liter. Calculate the pH of water.
Ex: Determine the pH of a 0.001-M HCl solution.
Ex: What is the pH of a 0.001-M NaOH solution
Solutions with a pH < 7 are acidic
Solutions with a pH > 7 are basic
Solutions with a pH = 7 are neutral
15,16-12
A titration is the controlled addition and measurement of the amount of a solution of known concentration required to react completely with a measured amount of a solution of unknown concentration.
An equivalence point is the point at which the two solution used in a titration are present in chemically equivalent amounts.
An end point is the point in a titration at which an indicator changes color.
A standard solution contains the precisely known concentration of a solute.
A primary standard is a highly purified solid compound used to check the concentration of the know solution in a titration.