acids and bases
DESCRIPTION
Acids and Bases. Ionization of Water. Only happens to a small amount of water molecules H 2 O separates into H + and OH - Not the whole story H+ never occurs on its own In reality, another H 2 O molecule picks it up and becomes H 3 O + (hydronium ion). Acids and Bases. - PowerPoint PPT PresentationTRANSCRIPT
Ionization of Water Only happens to a small amount of water
molecules H2O separates into H+ and OH-
Not the whole story H+ never occurs on its own In reality, another H2O molecule picks it up and
becomes H3O+ (hydronium ion)
Acids and Bases
Acids Bases
Taste sour Taste bitter
Feel watery Feel slippery
Conduct electricity Conduct electricity
Change litmus to red Change litmus to blue
pH = 0-7 pH = 7-14
Neutralize bases Neutralize acids
Classifying Acids and Bases Arrhenius
Acid- substance that dissociates into H+ and an anion For Example: HCl and H2SO4
Base- substance that dissociates into cation and OH-
For example: NaOH and Mg(OH)2
Does not explain bases without an OH ion
Classifying Acids and Bases (cont) Brønsted-Lowry
Acid - Proton (H+) donor For example: HCl and H2SO4
Base - Proton (H+) acceptor For example: NH3 and OH-
Conjugate Acid and Bases Occur on the other side of acid base equations. Lets look again at
NH3 is a base. It will accept a proton (H+) H2O is an acid. It will donate a proton (H+) NH4
+ is NH3’s conjugate acid. It can donate a proton (H+) to become NH3 again
OH- is water’s conjugate base. It can accept a proton (H+) to become H2O again
Amphiprotic Amphiprotic –
Substances that can act like an acid or a base Water is an amphiprotic substance.
H2O can accept a proton to become H3O+
H2O can donate a proton to become OH-
Strength of Acids and Bases Depends on how much they dissociate in
water Strong
Considered to dissociate completely in water Weak
Only partially dissociate in water Reaction is reversible ()
Conjugate pairs Strength is inversely proportional
For example: Strong acids have weak conjugate bases
Acids Strong acids
HI HBr HCl HNO3
H2SO4
HClO4
HClO3
All have 100% of the molecules break apart. There is no reverse reaction.
Weak acids All others
Polyprotic Acids Have multiple H’s H2SO4
H2SO4 gives up 1 H+ to form HSO4-
This happens to 100% of the molecules since H2SO4 is strong
HSO4- gives up another H+ to form SO4
-2
This only happens to some HSO4- because it is weak
Solution will contain A lot of water molecules H3O+ molecules (mostly from the first H+ but some from the
second and from ionization of water) HSO4
-
a little bit of SO4-2
A little bit of OH- (from the ionization of water)
Acid Names Binary acids (H with an element)
Prefix hydro- Root of element name Suffix –ic Add acid For example: HCl is hydrochloric acid
Acids with Oxygen (H with a polyatomic) Root name of polyatomic (with polyatomic prefix if applicable)
Some polyatomic roots are modified slightly to be easier to say Suffix
-ic with polyatomics ending in –ate -ous with polyatomics ending in -ite
Add acid For example: H2SO4 is sulfuric acid
Bases Strong bases
Group 1 metals with OH-
Ca, Sr, and Ba with OH-
These three are not very soluble in water, but the amount that does dissolve ionizes completely.
Weak bases All others
Chemical Equilibrium Reversible reactions Indicated with a
Both reactions are happening at the same time System reaches equilibrium when both are happening at
same rate At equilibrium
Could have lots of reactant and little product Could have lots of product and little reactant Could have equal amounts of both
Changes to the system can shift equilibrium Temperature Pressure Adding reactants or products
Equilibrium Expressions Mathematical way to represent equilibrium For the equation, aA + bB cC + dD
K = [C]c [D]d
[A]a [B]b
K is the equilibrium constant for the equation [ ] indicates the concentration of each substance
in mol/L (M) Solid and pure liquids are not entered into the
expression
Ionization of Water 2H2O(l) H3O+(aq) + OH-(aq)
This equilibrium “lies to the left” In other words, there is far more water molecules than
hydronium and hydroxide ions in a sample
Kw = [H3O+] [OH-] Kw = 1.0 x 10-14
In pure water and neutral solutions, [H3O+] and [OH-] are 1.0 x 10-7 M
In acidic solutions, [H3O+] is greater than [OH-] In basic solutions [OH-] is greater than [H3O+]
pH pH
Stands for potential of Hydrogen (really hydronium)
Logarithmic scale pH = -log [H+] or [H+] = 10-pH
Values between 0-14 with each number representing a 10-fold increase from the previous number pH 7 is acidic pH = 7 is neutral pH 7 is basic
pOH pOH = -log [OH-] or [OH-] = 10-pOH
Opposite scale pOH 7 is basic pOH = 7 is neutral pOH 7 is acidic
Neutralization (Acid-Base Reaction) Special type of double displacement reaction Acid + Base Water + Salt
Titration Process of neutralizing an acid (or base) with an
unknown concentration with a base (or acid) of a known concentration
Moles of H3O+ must equal moles of OH- for neutralization to occur
Often indicators are used to determine the end of the reaction
VaMa = VbMb
Va = volume in L of acid Ma = molarity of acid Vb = volume in L of base Mb = molarity of base