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Week 5 Chemie
Hoofdstuk 10 Acids and Bases
A few facts about acids and bases :
An acid is a substance that produces hydrogen ions, H+, when dissolved in water
A base is a substance that produces hydroxide ions, OH-, when dissolved in water
The neutralization reaction of an acid with a base yields water plus a salt, an ionic compound
composed of the cation from the base and the anion from the acid.
But there is a issue, the H+ ion is so reactive that is does not exist in water. Instead, H+ reacts with
H2O to give the hydronium ion H3O+. It is important to realise that the OH- ions produced by the base
can come from either of two sources. Metal hydroxides (NaOH, KOH) are ionic compounds that already
contain OH- ions and merely release those ions when they dissolve in water. But, metal oxides can also
react with water to generate OH- ions. In addition, some molecular compounds are not ionic and
contains no OH- ions in their structure. Nonetheless, they can act as bases to produce OH- ions in
reactions with water.
The Arrhenius definition of acids and bases applies only to processes that take place in an aqueous
solution. A Bronsted-Lowry acid is any substance that is able to give a hydrogen ion to another
molecule or ion. A Bronsted-Lowry base is a substance that can accept H+ ions from an acid. A base
can either be neutral or negatively charged. If the base is neutral, the product will be positively
charged.
An important consequence of the Bronsted-Lowry definition is that the products of an acid-base
reaction can also behave as acids and bases.
Pairs of chemical species such as B, BH+ and HA, A- are called conjugate acid base pairs. They are
species that are found on opposite sides of a chemical reaction whose formulas differ by only one H+.
Thus the product anion A- is the conjugate base of the reactant acid HA, and HA is the conjugate acid
of the base A-.
Acids differ in their ability to give up a proton. A strong acid gives up H+ easily and completely
dissociates in water. Dissociates = the splitting apart of an acid to give H+ and an anion. A weak acid
gives up H+ with difficulty and does not completely dissociates in water.
Week 5 Chemie 1
, A weak base has only a slight affinity for H+ and holds it weakly, a strong base has a high affinity for
H+ and holds it tightly.
The stronger the acid, the weaker its conjugate base ; the weaker the acid, the stronger its
conjugate base. An acid-base protontransfer equilibrium always favors reaction of the stronger
acid with the stronger base and formation of the weaker acid and base.
The proton will always leave the stronger acid (whose stronger conjugate base cannot hold the proton)
and always ends up in the weaker acid (whose stronger conjugate base holds the proton)
Acid dissociation constant (Ka) = The equillibrium constant for the dissociation of an acid.
Week 5 Chemie 2
Week 5 Chemie
Hoofdstuk 10 Acids and Bases
A few facts about acids and bases :
An acid is a substance that produces hydrogen ions, H+, when dissolved in water
A base is a substance that produces hydroxide ions, OH-, when dissolved in water
The neutralization reaction of an acid with a base yields water plus a salt, an ionic compound
composed of the cation from the base and the anion from the acid.
But there is a issue, the H+ ion is so reactive that is does not exist in water. Instead, H+ reacts with
H2O to give the hydronium ion H3O+. It is important to realise that the OH- ions produced by the base
can come from either of two sources. Metal hydroxides (NaOH, KOH) are ionic compounds that already
contain OH- ions and merely release those ions when they dissolve in water. But, metal oxides can also
react with water to generate OH- ions. In addition, some molecular compounds are not ionic and
contains no OH- ions in their structure. Nonetheless, they can act as bases to produce OH- ions in
reactions with water.
The Arrhenius definition of acids and bases applies only to processes that take place in an aqueous
solution. A Bronsted-Lowry acid is any substance that is able to give a hydrogen ion to another
molecule or ion. A Bronsted-Lowry base is a substance that can accept H+ ions from an acid. A base
can either be neutral or negatively charged. If the base is neutral, the product will be positively
charged.
An important consequence of the Bronsted-Lowry definition is that the products of an acid-base
reaction can also behave as acids and bases.
Pairs of chemical species such as B, BH+ and HA, A- are called conjugate acid base pairs. They are
species that are found on opposite sides of a chemical reaction whose formulas differ by only one H+.
Thus the product anion A- is the conjugate base of the reactant acid HA, and HA is the conjugate acid
of the base A-.
Acids differ in their ability to give up a proton. A strong acid gives up H+ easily and completely
dissociates in water. Dissociates = the splitting apart of an acid to give H+ and an anion. A weak acid
gives up H+ with difficulty and does not completely dissociates in water.
Week 5 Chemie 1
, A weak base has only a slight affinity for H+ and holds it weakly, a strong base has a high affinity for
H+ and holds it tightly.
The stronger the acid, the weaker its conjugate base ; the weaker the acid, the stronger its
conjugate base. An acid-base protontransfer equilibrium always favors reaction of the stronger
acid with the stronger base and formation of the weaker acid and base.
The proton will always leave the stronger acid (whose stronger conjugate base cannot hold the proton)
and always ends up in the weaker acid (whose stronger conjugate base holds the proton)
Acid dissociation constant (Ka) = The equillibrium constant for the dissociation of an acid.
Week 5 Chemie 2
