Acids and Bases pH Buffers and Problems

Acids and Bases

Acids and Bases Practice links

pH Buffers and Problems

 

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Acids Bases pH  Buffers and Problems related to each of these sections

 

Buffers


Three theories for acids and bases
1. Arrhenius Theory
2. Bronsted-Lowry Theory of acids and bases
3. Lewis Acids and BasesIonisation
Molecular compounds that are polar can undergo breaking up into ions with the help of water molecules (Undergoes hydration)Hydronium Ions
The process of hydration or ionization leads to the formation of Hydronium ions
HA + H2O → H3O+ + A Dissociation
Ionic compounds break up into ions in aqueous solution this is referred to as dissociation eg. NaCl, KNO3 etc
Acids and BasesArrhenius Theory of acids and Bases:Arrhenius Acids:
Acids are substances which dissolve in water to increase the hydrogen ion or hydronium ion concentration.
Eg.
HCl(aq) → H+(aq) + Cl (aq)

H+ ions being very small cannot exist by itself, they exist as hydronium ion or [H3O+]

HNO3

H2SO4

Strong acids
Strong acids are those acids which have a > 99 % ionization

Weak Acid
Acetic Acid
Hydro cyanic Acid
Hydrofluoric Acid
Methanoic Acid
Ethanoic Acid

Arrhenius Bases:
According to this theory Arrhenius bases are substances which produce OH ions when dissolved in water or in aqueous solution.
NaOH, KOH, Ca(OH)2 etc
Strong bases
Bases that undergo 100 % ionisation are called strong bases
Examples:
Strong Bases:
Sodium Hydroxide
Potassium Hydroxide
Barium Hydroxide

Weak Bases

Ammonium Hydroxide
Sodium Carbonate

Substances that dissolve in water to increase the hydroxide ion concentration are considered to be bases.
Eg.
NaOH → Na+(aq), + OH (aq)
Ca(OH)2 → Ca2+ (aq) + 2 OH (aq)

Degree of ionization
Degree of ionization is an indicator of weather the acid is strong and weak

Neutralization reactions:
The reaction between an acid and a base is referred to a neutralisation.
An acid and a base react to give salt and water.
The reaction is exothermic.
The enthalpy of neutralisation for a strong acid and a strong base is found to be –57kj/mol

Write the reaction and equations involved in the reaction between Acids and Bases?
Example: Nitric acid and Sodium Hydroxide,
Sulphuric acid and Potassium hydroxide,
Phosphoric acid and Sodium Hydroxide,
Ethanoic acid and Calcium hydroxide,
pH scale
The scale was introduced by Sorensen.
May be defined as the –log of the Hydrogen ion concentration written as
pH = -log [H+]
The strength of an acid or base can be deduced from the pH value
pH = -log [H+] or [H+] = 10-pH

pH Range 0 to 14
7 neutral
< 7 Acidic , >7 Basic

If the difference of pH between two acids is 1 what does it mean?

If the difference in pH between two liquids is 2 what does it mean?

Check Summary of Acids and Bases page 385


Lowry Bonsted concept of Acids and Bases

An Acid is a proton donor. A Base is a proton Acceptor
Conjugate Acid and Conjugate base:
Examples:
HCl + H2O → H3O+ + Cl All are aqueous solutions
Acid Base Conjugate Acid Conjugate Base

NH3 + H2O → NH4+ + OH All are aqueous solutions
Base Acid Conjugate Acid Conjugate Base

Identify the acid, base, conjugate acid & conjugate base in the following reactions

H2SO4 + HCO3

H3PO4 + OCl

H3O+ + HSO3

Amphiprotic

Some general aspects of acids and bases, substance that can either accept or donate a proton is referred to as an amphiprotic compound eg. Water is an example.

Illustrated with water as an example as in the above examples

HCO3 + H3O+ → H2CO3 + H2O All are aqueous solutions
Base Acid Conjugate Acid Conjugate Base

HCO3 + OH → CO32‑ + H2O All are aqueous solutions
Acid Base Conjugate Base Conjugate Acid

An acid and a conjugate base differ by a proton.
Similarly a base and a conjugate acid differ by a proton.

Titration

If you are performing a titration make sure you calibrate the pH sensor with the Lab quest. pH 4 and 10 should be used. Proceed with the experiment only after calibrating the device.
If the titration is done only with a pH meter set up the sensor to the mode “Events with Entry”

Titration and pH curves:

Acids Bases pH  Buffers and Problems

Acids Bases pH  Buffers and Problems

Acid Base
Acids and Bases in a Cup