RAYPUNG acids and bases
21.6 Brønsted Lowry Acid Base Reactions
Conjugate Acids and Bases
Brønsted-Lowry Acid-Base Reactions
Neutralization Reaction
2H2O + ⇄ H3O^+ + OH^-
HA + B⇄A- + BH
acid + base ⇄ conjugate base + conjugate acid
A conjugate acid is the particle produced when a base accepts a proton.
When a substance that is acting as a Brønsted-Lowry acid donates its proton, it becomes a base in the reverse reaction.
A conjugate acid-base pair is a pair of substances related by the loss or gain of a single hydrogen ion.
A conjugate base is the particle produced when an acid donates a proton.
An acid-base reaction according to the Brønsted-Lowry definition is a transfer of a proton from one molecule or ion to another.
NH3(aq)+H2O(l)⇄NH^+4(aq)+OH^−(aq)
base acid acid base
the reverse reaction
There is one acid and one base as reactants, and one acid and one base as products.
HSO＾−4(aq)+H2O(l)⇄H3O＾+(aq)+SO2＾−4(aq) acid base acid base
the reaction of water with the hydrogen sulfate ion.
An amphoteric substance is one that is capable of acting as either an acid or a base by donating or accepting hydrogen ions.
21.5 Brønsted-Lowry Acids and Bases
Brønsted-Lowry Acids and Bases
What kind of molecule would qualify as a Brønsted-Lowry base?
The Arrhenius concept of acids and bases
⭐ replaced and expanded the original idea of Lavoisier that all acids contained oxygen
⭐ this concept did not deal with acid-base behavior in solvents such as benzene where there could be no ionization
1923, a broader definition of acids and bases was independently proposed by Danish chemist Johannes Brønsted and English chemist Thomas Lowry.
✏A Brønsted-Lowry base is a molecule or ion that accepts a hydrogen ion in a reaction.
✏A hydrogen ion is commonly referred to as a proton, and so acids and bases are proton donors and proton acceptors respectively according to the Brønsted-Lowry definition.
e.g. ammonia (NH3). It is base. However, it does not contain the hydroxide ion.
Oxygen is another atom with lone pair electrons that can function as Brønsted-Lowry bases.
These molecules need to be able to accept a hydrogen ion (or proton).
✅ an anion that can form a neural compound with a proton
✅ a molecule in which one or more atoms has lone-pair electrons
Electrons in an oxygen atom.
B/L acids: donate H+
B/L bases: accept a H+
21.8 Self Ionization of Water
The Ion-Product of Water
The self-ionization of water occurs to a very limited extent.
The self-ionization of water occurs to a very limited extent.
the process in which water ionizes to hydronium ions and hydroxide ions
When two molecules of water collide, there can be a transfer of a hydrogen ion from one molecule to the other.
The products are a positively charged hydronium ion and a negatively charged hydroxide ion.
H2O(l)+H2O(l)⇄H3O^+(aq)+OH^−(aq)
H2O(l)⇄H^+(aq)+OH^−(aq)
Kw
Kw=[H^+][OH^−]
The ion-product of water (Kw) is the mathematical product of the concentration of hydrogen ions and hydroxide ions.
At 25°C, the experimentally determined value of Kw in pure water is 1.0 × 10-14.
Kw=[H+][OH−]=1.0×10−14
[H+]=[OH−]=1.0×10−7 M
Sample Problem
Hydrochloric acid (HCl) is a strong acid, meaning it is 100% ionized in solution. What is the [H+] and the [OH−] in a solution of 2.0 × 103 M HCl?
Known
[HCl] = 2.0 × 10^-3 M
Kw=1.0×10^−14
Unknown
[H+] = ? M
[OH-] = ? M
[H+]=2.0×10−3 M
Kw=[H+][OH−]=1.0×10^−14
[OH−]=Kw/[H+]=1.0×10^−14/2.0×10^−3=5.0×10^−12 M
acidic solution
the concentration of hydrogen ions is greater than the concentration of hydroxide ions.
HCl(g)→H+(aq)+Cl−(aq)
hydrogen chloride ionizes to produce H+ and Cl− ions upon dissolving in water.
This increases the concentration of H+ ions in the solution.
According to LeChâtelier’s principle, the equilibrium represented by H2O(l)⇄H+(aq)+OH−(aq) is forced to the left, towards the reactant. As a result, the concentration of the hydroxide ion decreases.
basic solution
the concentration of hydroxide ions is greater than the concentration of hydrogen ions.
KOH(s)→K+(aq)+OH−(aq)
Solid potassium hydroxide dissociates in water to yield potassium ions and hydroxide ions.
The increase in concentration of the OH− ions causes a decrease in the concentration of the H+ ions and the ion-product of [H+][OH−] remains constant
21.9 pH
WHERE ARE YOUR NOTES ON THE VIDEO, OR THE ANSWERS TO THE REVIEW QUESTIONS?
The pH Scale
pH of acids and bases
Danish scientist Søren Sørenson (1868-1939) proposed an easier system for indicating the concentration of H+ called the pH scale.
The letters pH stand for the power of the hydrogen ion. The pH of a solution is the negative logarithm of the hydrogen-ion concentration.
Formulas
pH = -log[H+]
a solution with the [H+] higher than 1.0 × 10-7 is acidic
a solution with the [H+] lower than 1.0 × 10-7 is basic
Consequently, solutions whose pH is less than 7 are acidic, while those with a pH higher than 7 are basic.
coffee
tomato juice
eggs
blood
pH3
pH9.5
21.17 Titration Experiment
YOU NEED MORE DETAILS HERE
In the neutralization of hydrochloric acid by sodium hydroxide, the mole ratio of acid to base is 1:1.
HCl(aq)+NaOH(aq)→NaCl(aq)+H2O(l)
procedure
Several drops of an indicator are added to the acid and mixed by swirling the flask.
A buret is filled with the base solution of known molarity.
A measured volume of an acid of unknown concentration is added to an Erlenmeyer flask.
The stopcock of the buret is opened and base is slowly added to the acid while the flask is constantly swirled to insure mixing. The stopcock is closed at the exact point at which the indicator just changes color.
standard solution
the solution in a titration
21.18 Titration Calculations
You need to make sure you are using your OWN words when taking notes, otherwise, the mind map just becomes a cut/paste exercise that does not help your learning. Mind maps are a powerful tool when properly used.
Titration Calculations
moles acid=moles base
At the equivalence point in a neutralization, the moles of acid are equal to the moles of base.
moles solute=M×L
Recall that the molarity (M) of a solution is defined as the moles of the solute divided by the liters of solution (L).
the moles of solute are therefore equal to the molarity of a solution multiplied by the volume in liters.
MA×VA=MB×VB
MA is the molarity of the acid, while MB is the molarity of the base. VA and VB are the volumes of the acid and base, respectively.
MA=MB×VBVA=0.500 M×20.70 mL15.00 mL=0.690 M
The higher molarity of the acid compared to the base in this case means that a smaller volume of the acid is required to reach the equivalence point.