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chemistry 2y > Solutions & Electrochemistry > Flashcards

Solutions & Electrochemistry Flashcards

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1
Q

What is molarity (M)?

A

Molarity is the number of moles of solute per litre of solvent (mol/L)

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2
Q

How do you calculate molarity (M)?

A

M = no. moles of solute / litres of solvent

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3
Q

What is molality (m)?

A

Molality is the number of moles of solute per kg of solvent

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4
Q

How do you calculate molality (m)?

A

m = number of moles of solute / kg of solvent

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5
Q

What is mole fraction (X)?

A

Mole fraction is the relative of a solute within a mixture/solution

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6
Q

How do you calculate mole fraction (X)?

A

X = moles of solute / total moles of solution (it is unitless)

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7
Q

What is the equation to calculate the chemical potential of an ideal gas (u)?C

A

u = u* + RT ln P/P*
u = chemical potential
u* = chemical potential under standard conditions
R = gas constant
T = temp (K)
P = pressure
P* = standard pressure (1 atm)

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8
Q

What is another word for molar Gibbs energy?

A

Chemical potential

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9
Q

How is Gibbs energy and chemical potential related?

A

Chemical potential = Gibbs energy / no. moles

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10
Q

What are colligative properties?

A

The properties of a solution that depend solely on the number of solute particles in the solution, and not on their chemical identity

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10
Q

When does a liquid boil?

A

When the vapour pressure of a liquid becomes equal to the external pressure

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11
Q

What is Raults equation for vapour pressure (non-volatile solutes)?

A

Ps = Xs x Ps
Where
Ps is vapour pressure of solution
Xs is molar fraction of solvent
Ps is vapour pressure of pure solvent

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12
Q

What is a positive deviation wrt Raults law?

A

When the observed vapour pressure is greater than that predicted by Raoult’s law

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13
Q

What does a positive deviation mean on a molecular level?

A

It is easier (than predicted) for molecules to enter the vapour phase, which implies weaker intermolecular interactions in the mixture between pure and solvent molecules

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14
Q

What is a negative deviation wrt Raults law?

A

When the observed vapour pressure is less than that predicted by Rault’s law

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15
Q

What does a negative deviation mean on a molecular level?

A

It is harder (than predicted) for molecules to enter the gaseous phase, implying stronger intermolecular interactions in the mixture than between pure solvent molecules

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16
Q

What is osmotic pressure?

A

The external pressure that must be applied to prevent solvent passing through the membrane

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16
Q

What is the equation for osmotic pressure (if the solution acts ideally)?

A

Osmotic pressure (II) = i x M x R x T
Where
i = Van’t Hoff Factor
R = gas constant (must be the correct form)
M = molarity of the solution
T = temperature of solution (K)

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16
Q

How does osmotic pressure change for different solutes (ideally)?

A

They don’t change. At the same molar concentration, all
solutes give the same osmotic pressure if the solutions act ideally

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17
Q

What is the correct form of gas constant for osmotic pressure calculations?

A

0.082

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18
Q

What is the equation for working out change in chemical potential?

A

C.I chemical potential = R x T x lnXsolvent

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19
Q

What is freezing point depression?

A

When the freezing point of a solution is lower when a solute is added to the solvent, compared to that of a pure solvent

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20
Q

What is the equation for change in freezing point temperature upon addition of a solute?

A

C.I Tf = i x kf x m
Where
i = Van’t Hoff factor
kf = solvent-dependent freezing point constant
m = molality of the solute

21
Q

What is the Van’t Hoff factor (i)?

A

A factor used to represent the number of particles that a solute compound will dissociate into when it is dissolved into a solution

22
Q

What is the Van’t Hoff factor of sugars?

A

1, as the sugar molecule remains intact in solution (doesn’t dissociate)

23
Q

What is the equation to determine the Van’t Hoff factor?

A

i = no. particles after dissociation / number of formula units initially added

24
Q

What are some example Van’t Hoff values?

A

NaCl = 2
CaCl2 = 3
C6H12O6 (glucose) = 1

25
Q

What is boiling point elevation?

A

When a non-volatile solute is added to a solvent, it can disrupt the formation of vapour molecules on the surface of the solution, leading to an increase in boiling point.

26
Q

What factors affect boiling point elevation?

A

Stronger solute-solvent interactions or higher solute concentration results in a greater boiling point elevation

27
Q

What is the equation for boiling point elevation?

A

C.I Tb = i x kb x m
Where
i = Van’t Hoff factor
kf = solvent-dependent boiling point constant
m = molality of the solute

28
Q

What is the Van’t Hoff value for weak acids?

A

They will not fully dissociate, so the value will be 1 < i < 2

29
Q

What is dimerisation?

A

Where two identical entities combine to form a dimer through intermolecular forces (e.g. H bonding)

30
Q

What is activity (ax)?

A

The effective concentration of species X in the solution- the activity is always less than or equal to concentration

31
Q

What is the formula for activity (ax)?

A

ax = yx x [X]
Where
yx is the activity coefficient
[X] is concentration of species X

32
Q

What is the formula for ionic strength (I)?

A

I = 1/2 the sum of [X] x zx^2 and [Y] x zy^2
Where
[X] = the molality of ion X
zx = the charge of ion X
[Y] = the molality of ion Y
zy = the charge of ion Y

33
Q

What are the main takeaways from the Debye-Huckel limiting law?

A
  • The higher the ionic strength, the lower the ion activity coefficient
  • It only applies to very dilute solutions (<0.001 mol/kg)
34
Q

What law is used to describe the behaviour of solutions with a concentration of 0.001 mol/kg < I < 1 mol/kg

A

Extended Debye-Huckel laws

35
Q

What are the two types of electrochemical cells?

A

Galvanic/Voltaic cells
Electrolytic cells

36
Q

What are Galvanic/Voltaic cells?

A

Cells that react spontaneously to generate electricity (e.g. batteries)

37
Q

What are electrolytic cells?

A

Cells that use electricity to perform a chemical reaction (e.g. splitting of water for hydrogen production0

38
Q

How do you calculate standard cell potential?

A

Ecell = Ecathode - Eanode = Erhs - Elhs
Where
Ecathode/Erhs = the reduction potential of the cathode (which is on the right hand side)
Eanode/Elhs = the reduction potential of the anode (which is on the left hand side)

39
Q

In terms of half potentials, what needs to be the vase for a reaction to proceed spontaneously?

A

If Ecathode - Eanode = >0, the reaction is spontaneous
If it is <0, it is not spontaneous

40
Q

What is the equation relating Gibbs energy and reaction quotient?

A

C.I Gibbs - RT ln (Q/K)
Where
Q = reaction quotient
K = equilibrium constant

41
Q

What is C.I Gibbs energy equivalent to?

A

The maximum amount of work that can be done

42
Q

What is the equation relating Gibbs and Ecell?

A

C.I Gibbs = - n x F x Ecell
Where
n = no. electrons transferred
F = Faraday’s constant in C/mol

43
Q

What is n x f analogous to in the W = I x V equation?

A

n x f is analogous to I (current)

44
Q

What is Ecell analagous to in the W = I x V equation?

A

Ecell is analogous to V (volatage)

45
Q

What is value of Faraday’s constant (F)?

A

96485 c/mol

46
Q

What charge is the cathode in electrolytic cells?

A

The cathode is negative in electrolytic cells, as it connected to a negative power supply

47
Q

What charge is the anode in electrolytic cells?

A

The anode is positive in electrolytic cells, as it is connected to a positive power supply

48
Q

Where does reduction occur in galvanic cells?

A

At the cathode

49
Q

Where does reduction occur in electrolytic cells?

A

At the cathode

50
Q

Where do cations go in galvanic and electrolytic cells, and why?

A

In both galvanic and electrolytic cells, the cations migrate to the cathode, as that is where reduction occurs, and hence where the cations gain electrons (Reduction Is Gain)

51
Q

How do you work out the mass of metal M deposited at the cathode in an electrolytic cell?

A

mM = (I x t x mM) / (F x z)
where
I = current supplied to the cell in AMPS
t = time in SECONDS
mM = the metal’s molar mass
F = Faraday’s constant
z = the valence of the metal

52
Q

What are primary cells?

A

Electrochemical cells in which the chemical reactions that generate electric current are irreversible. They cannot be recharged. They are also known as non-rechargeable/disposable cells

53
Q

What are secondary cells?

A

Electrochemical cells in which the chemical reactions that generate electric current are reversible.
This means that secondary cells can be recharged
by applying an external electrical current to reverse the chemical reactions and restore the cell to a charged state.

chemistry 2y (7 decks)

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