CHEM 230 EXAM 2+3 QUESTIONS & ANSWERS
What is the principal form of benzoic acid at pH 8.2 if the pKa value is 4.2 - Answer -
So, at pH 4.20, there is a 1:1 mixture of benzoic acid (HA)
and benzoate ion (A-). At pH = pKa + 1 (= 5.20), the quotient [A-]/[HA] is 10:1. At
pKa + 2 (= 6.20), the quotient [A-]/[HA] is 100:1. As pH increases, all the way to pKa + 4
the [A-]/[HA] is 10000:1
*The predominant form of benzoic acid at pH 8 is the benzoate anion
For a monoprotic system, the species ___ is the predominant form when pH > pKa. -
Answer -the basic species A- is the predominant form when pH > pKa.
The species ___ is the predominant form when pH < pKa. - Answer -HA is the
predominant form when pH < pKa.
A- is basic/acidic?
HA is basic/acidic? - Answer -A- is basic
HA is acidic
Speciation describes describes what? - Answer -the distribution of analyte among
possible species.
For an acid or base, speciation describes how much of each protonated form is present.
Activity - Answer -Accounts for the ionic strength in a chemical reaction
Activity coefficient measures the deviation from 1
As the ionic strength increases the coefficient goes towards ____
As the ionic strength decreases the coefficient goes towards ____ - Answer -As the
ionic strength increases, the activity coefficient decreases towards 0
As the ionic strength decreases, the activity coefficient increases towards 1
As the magnitude of charge of an ion increases, the activity coefficient ____ - Answer -
decreases
Fractional Composition - Answer -The portion of a given ion in a solution
Redox Reaction - Answer -When electrons from a redox reaction flow through an
electric circuit, current and voltage can be measured
In a redox reaction Current is proportional to ___ and Voltage is proportional to ____ -
Answer -Current is proportional to the rate of reaction
Voltage is proportional to the free energy change for the reaction
, Electric Charge
q=n*F
where q n & F = __ __ and __ - Answer -q= electric charge (C)
n= moles of electrons transferred
Faraday constant (F)= electric charge of one mole of electrons
9.649*104 C/mol
Electric Current
𝐼= 𝑞/𝑡
where I q & t = __ __ & __ - Answer -I= current (A)
q= charge (C)
t= time (s)
Ohm's Law - Answer -Current is proportional to potential difference (voltage) across a
circuit and inversely proportional to resistance
I = E/R
Current is proportional to ____ - Answer -proportional to potential difference (voltage)
across a circuit
Current is inversely proportional to ____ - Answer -inversely proportional to resistance
work= E*q
where E & q = __ & __
and is measured in ___ - Answer -E= electric potential- energy in Joules needed to
bring one coulomb of positive charge to a point (V= J/C)
q= electric charge (C)
measure in Joules (J)
Gibb's Free Energy - Answer -Maximum possible electrical work that can be done by
the reaction on its surroundings
delta(G)= - work= - E*q= - E(nF)
A species is oxidized when it loses/gains electrons - Answer -loses
A species is reduced when it loses/gains electrons - Answer -gained
An oxidizing agent (oxidant) gains electrons from another substance and becomes ____
- Answer -reduced
An oxidizing agent (oxidant) ____ electrons from another substance and becomes
reduced - Answer -gains
What is the principal form of benzoic acid at pH 8.2 if the pKa value is 4.2 - Answer -
So, at pH 4.20, there is a 1:1 mixture of benzoic acid (HA)
and benzoate ion (A-). At pH = pKa + 1 (= 5.20), the quotient [A-]/[HA] is 10:1. At
pKa + 2 (= 6.20), the quotient [A-]/[HA] is 100:1. As pH increases, all the way to pKa + 4
the [A-]/[HA] is 10000:1
*The predominant form of benzoic acid at pH 8 is the benzoate anion
For a monoprotic system, the species ___ is the predominant form when pH > pKa. -
Answer -the basic species A- is the predominant form when pH > pKa.
The species ___ is the predominant form when pH < pKa. - Answer -HA is the
predominant form when pH < pKa.
A- is basic/acidic?
HA is basic/acidic? - Answer -A- is basic
HA is acidic
Speciation describes describes what? - Answer -the distribution of analyte among
possible species.
For an acid or base, speciation describes how much of each protonated form is present.
Activity - Answer -Accounts for the ionic strength in a chemical reaction
Activity coefficient measures the deviation from 1
As the ionic strength increases the coefficient goes towards ____
As the ionic strength decreases the coefficient goes towards ____ - Answer -As the
ionic strength increases, the activity coefficient decreases towards 0
As the ionic strength decreases, the activity coefficient increases towards 1
As the magnitude of charge of an ion increases, the activity coefficient ____ - Answer -
decreases
Fractional Composition - Answer -The portion of a given ion in a solution
Redox Reaction - Answer -When electrons from a redox reaction flow through an
electric circuit, current and voltage can be measured
In a redox reaction Current is proportional to ___ and Voltage is proportional to ____ -
Answer -Current is proportional to the rate of reaction
Voltage is proportional to the free energy change for the reaction
, Electric Charge
q=n*F
where q n & F = __ __ and __ - Answer -q= electric charge (C)
n= moles of electrons transferred
Faraday constant (F)= electric charge of one mole of electrons
9.649*104 C/mol
Electric Current
𝐼= 𝑞/𝑡
where I q & t = __ __ & __ - Answer -I= current (A)
q= charge (C)
t= time (s)
Ohm's Law - Answer -Current is proportional to potential difference (voltage) across a
circuit and inversely proportional to resistance
I = E/R
Current is proportional to ____ - Answer -proportional to potential difference (voltage)
across a circuit
Current is inversely proportional to ____ - Answer -inversely proportional to resistance
work= E*q
where E & q = __ & __
and is measured in ___ - Answer -E= electric potential- energy in Joules needed to
bring one coulomb of positive charge to a point (V= J/C)
q= electric charge (C)
measure in Joules (J)
Gibb's Free Energy - Answer -Maximum possible electrical work that can be done by
the reaction on its surroundings
delta(G)= - work= - E*q= - E(nF)
A species is oxidized when it loses/gains electrons - Answer -loses
A species is reduced when it loses/gains electrons - Answer -gained
An oxidizing agent (oxidant) gains electrons from another substance and becomes ____
- Answer -reduced
An oxidizing agent (oxidant) ____ electrons from another substance and becomes
reduced - Answer -gains
