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OCR B A Level Chemistry > oceans > Flashcards

Flashcards in oceans Deck (39)
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1
Q

give a reason why a substance might not dissolve

A

bonds to be broken are stronger than bonds to be made

2
Q

what interactions form between an ion and a polar solvent?

A

ion-dipole interactions

3
Q

define standard lattice enthalpy

A

the enthalpy change when 1 mole of an ionic lattice is formed from its gaseous ions under standard conditions

4
Q

define enthalpy change of hydration

A

enthalpy change when 1 mole of aqueous ions is formed from gaseous ions

5
Q

define enthalpy change of solution

A

enthalpy change when 1 mole of ionic substance dissolves in enough solvent to form an infinitely dilute solution

6
Q

how is charge density found?

A

charge/radius

7
Q

how does charge density affect lattice enthalpy?

A

ions with a higher charge density are better at attracting each other in a lattice; more exothermic lattice enthalpy

8
Q

how does charge density affect enthalpy of hydration?

A

ions with higher charge densities are better at attracting water molecules; more exothermic

9
Q

what is entropy?

A

a measure of the number of ways that particles can be arranged, and the number of ways energy can be shared out between them

10
Q

list the factors which affect amount of entropy present

A
  • physical state
  • amount of energy
  • number of moles
11
Q

what is the expression for total entropy change?

A

delta(tot)S= delta(sys)S + delta(surr)S

12
Q

how do you calculate entropy change of system? delta(sys)S

A

S(products) - S(reactants)

13
Q

how do you calculate entropy change of surroundings? delta(surr)S

A

-deltaH/T

remember deltaH must be in Jmol-1 NOT Kjmol-1

14
Q

what is a feasible reaction, and when is a reaction feasible in terms of delta(tot)S?

A
  • a feasible reaction is one that will carry on until completion without energy being supplied
  • total entropy change must be positive or zero
15
Q

what is solubility?

A

the maximum amount of solid which will dissolve in a certain solvent

16
Q

what is Ksp?

A

the equilibrium constant for a saturated solution of a sparingly soluble solid

17
Q

what is meant by the term ‘conjugate pair’?

A

the conjugate base of an acid is formed when the acid donates a proton
an equilibrium with conjugate pairs is set up the base dissolves in water

18
Q

what is the bronsted-lowry definition of a base

A

proton acceptors; accepts a proton from acid

19
Q

what is a neutral solution?

A

one which had [H+] = [OH-]

20
Q

how do you calculate pH?

A

-log10 [H+]

21
Q

how do you calculate [H+] from pH?

A

10^-pH

22
Q

how does water act as an acid and a base?

A

acts as an acid by donating a proton, and as a base by accepting one

23
Q

how do you calculate Ka for a weak acid?

A

Ka= [H+]^2/[HA]

24
Q

how do you convert pKa to Ka?

A

10^-pka

25
Q

what is a buffer?

A

a buffer is a solution that resists changes in pH when small amounts of acid or base are added

26
Q

what are the two types of buffer?

A

acidic and alkaline

27
Q

how do acidic buffers work?

A

they are made by mixing a weak acid with one of its salts
provides a solution with undissociated acid molecules and lots of salt molecules
equilibrium shifts to oppose a change

28
Q

how does equilibrium alter when a small amount of acid is added to a buffer?

A
  • [H+] increases

- equilibrium shifts left

29
Q

suggest two uses for buffers

A
  • shampoo

- biological washing powder

30
Q

what are the assumptions you make when you calculate the pH of a buffer

A
  • the salt is fully dissociated

- weak acid is only slightly dissociated, the equilibrium concentration is the same as its initial concentration

31
Q

how do greenhouse gases transfer energy?

A
  • they absorb IR which makes bonds vibrate

- extra vibrational energy is passed on to other molecules in the air by collisions

32
Q

what is the expression for Ka of water?

A

H20 = H+ + OH- then kw= [H+][OH-]

33
Q

why can H2O be removed from the expression for kw of water?

A

concentration of water is effectively constant, because water is present in excess/position of equilibrium lies far to the left

34
Q

what is defined as an acidic solution?

A

one in which [H+] > [OH-]

35
Q

what is defined as an alkaline solution?

A

one in which [H+] < [OH-]

36
Q

what assumptions do you make about buffer solutions?

A

1- all the A- ions come from the salt

2-almost all the HA molecules put into the buffer remain unchanged

37
Q

why is the pH of a buffer not affected by dilution?

A

when you add water, the concentrations of both the acid and the salt are reduced equally. the proportion remains the same

38
Q

what bonds are broken and made when a substance is dissolved?

A

bonds between solute broken, bonds between solute and solvent made

39
Q

how do you calculate the temperature at which a reaction can happen?

A

deltaH/deltasysS