oceans

Question 1

give a reason why a substance might not dissolve

Answer 1

bonds to be broken are stronger than bonds to be made

Question 2

what interactions form between an ion and a polar solvent?

Answer 2

ion-dipole interactions

Question 3

define standard lattice enthalpy

Answer 3

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

Question 4

define enthalpy change of hydration

Answer 4

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

Question 5

define enthalpy change of solution

Answer 5

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

Question 6

how is charge density found?

Answer 6

charge/radius

Question 7

how does charge density affect lattice enthalpy?

Answer 7

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

Question 8

how does charge density affect enthalpy of hydration?

Answer 8

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

Question 9

what is entropy?

Answer 9

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

Question 10

list the factors which affect amount of entropy present

Answer 10

• physical state
• amount of energy
• number of moles

Question 11

what is the expression for total entropy change?

Answer 11

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

Question 12

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

Answer 12

S(products) - S(reactants)

Question 13

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

Answer 13

-deltaH/T

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

Question 14

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

Answer 14

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

Question 15

what is solubility?

Answer 15

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

Question 16

what is Ksp?

Answer 16

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

Question 17

what is meant by the term ‘conjugate pair’?

Answer 17

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

Question 18

what is the bronsted-lowry definition of a base

Answer 18

proton acceptors; accepts a proton from acid

Question 19

what is a neutral solution?

Answer 19

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

Question 20

how do you calculate pH?

Answer 20

-log10 [H+]

Question 21

how do you calculate [H+] from pH?

Answer 21

10^-pH

Question 22

how does water act as an acid and a base?

Answer 22

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

Question 23

how do you calculate Ka for a weak acid?

Answer 23

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

Question 24

how do you convert pKa to Ka?

Answer 24

10^-pka

Question 25

what is a buffer?

Answer 25

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

Question 26

what are the two types of buffer?

Answer 26

acidic and alkaline

Question 27

how do acidic buffers work?

Answer 27

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

Question 28

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

Answer 28

- [H+] increases | - equilibrium shifts left

Question 29

suggest two uses for buffers

Answer 29

- shampoo | - biological washing powder

Question 30

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

Answer 30

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

Question 31

how do greenhouse gases transfer energy?

Answer 31

- they absorb IR which makes bonds vibrate | - extra vibrational energy is passed on to other molecules in the air by collisions

Question 32

what is the expression for Ka of water?

Answer 32

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

Question 33

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

Answer 33

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

Question 34

what is defined as an acidic solution?

Answer 34

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

Question 35

what is defined as an alkaline solution?

Answer 35

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

Question 36

what assumptions do you make about buffer solutions?

Answer 36

1- all the A- ions come from the salt | 2-almost all the HA molecules put into the buffer remain unchanged

Question 37

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

Answer 37

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

Question 38

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

Answer 38

bonds between solute broken, bonds between solute and solvent made

Question 39

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

Answer 39

deltaH/deltasysS