Oceans

Question 1

enthalpy change of solution

Answer 1

the energy change when a solid dissolves in solution

Question 2

enthalpy change of hydration of ions

Answer 2

the enthalpy change for the production of a solution of ions from one mole of gaseous ions

Question 3

lattice enthalpy

Answer 3

the enthalpy change when one mole of solid is formed by the coming together of separate ions (gaseous to solid state)

Question 4

ionic charge + ionic radii affecting lattice enthalpy

Answer 4

ionic charge - ions attract one another more strongly
ionic radius - ions can come closer together

Question 5

the more negative the lattice enthalpy..

Answer 5

the more insoluble the solid

Question 6

what is the sign of lattice enthalpy

Answer 6

negative because it is always exothermic because bonds are formed

Question 7

describe ion-dipole interactions

Answer 7

Charges on the water molecules are attracted to charges on the ions. the ions are separated from the lattice by water molecules and are now in solution/are hydrated

Question 8

The stronger the binding of the water molecules to the ions..

Answer 8

the more extensively hydrated the ions are

Question 9

how does ionic radius and charge density affect enthalpy of hydration

Answer 9

The smaller, higher charged ions can get closer to water molecules and attract them more strongly so more energy is given out when bonds form so enthalpy of hydration is more negative. This also makes the hydrated ion larger.

Question 10

sign of hydration enthalpy

Answer 10

negative, it is exothermic because bonds are made

Question 11

Enthalpy change of solution is the difference between..

Answer 11

that of hydration of ions and that of the lattice enthalpy

Question 12

sign of enthalpy for breaking the lattice

Answer 12

positive because negative lattice enthalpy is the change when the lattice is created

Question 13

If the enthalpy of solution is slightly positive..

Answer 13

the ionic solute can still dissolve despite being energetically unfavourable, as long as entropy increases

Question 14

effect on entropy when a solute dissolves

Answer 14

entropy increases because it becomes more disordered

Question 15

explain why ionic solids are insoluble in non polar solvents

Answer 15

there are no regions of positive/negative charge so they cannot interact to form bonds. Enthalpy of solution is too positive for the ions to dissolve as a result.

Question 16

normal greenhouse effect

Answer 16

The sun emits mainly UV and visible radiation, of which some is absorbed by earth and its atmosphere and the rest is reflected into outer space
The earth is now heated with this absorbed radiation
It radiates some of the radiation, mainly infrared
Water molecules absorb certain frequencies of radiation, the IR window is the frequencies that water does not absorb. Greenhouse gases like CO2 and CH4 absorb radiation in the IR window.
IR is absorbed by bonds in greenhouse gases causing these bonds to vibrate more
Vibrational energy is transferred to other molecules in the atmosphere, oxygen and nitrogen, by collisions
This increases the kinetic energy of molecules in the atmosphere
Some IR the molecules absorb is reemitted back towards earth to heat it further or outer space

Question 17

enhanced greenhouse effect

Answer 17

Too much CO2 and CH4 are released due to human activity so more radiation is absorbed than reemitted so the temperature of the atmosphere is increasing, resulting in global warming.

Question 18

describe the BL theory of acids and bases

Answer 18

Acids are proton donors, bases are proton acceptors
Once an acid has donated a base there is always the possibility that it can take back the proton, this results in acid/base pairs

Question 19

define conjugate acid and conjugate base

Answer 19

can donate a proton, has a positive charge
can accept a proton, has a negative charge

Question 20

explain why a strong acid has a weak conjugate base

Answer 20

the acid has a strong tendency to donate protons so the conjugate base will have a weak tendency to accept them back

Question 21

strength of an acid refers to..

Answer 21

how powerful a proton donor it is

Question 22

characteristics of weak acids

Answer 22

A weaker tendency to donate protons and it does not dissociate completely when dissolved in water

Question 23

describe where POE is for weak and strong acids

Answer 23

the weaker the acid, the further left
the stronger the acid, the further right because full dissociation has occurred

Question 24

characteristics of a strong acid

Answer 24

A stronger tendency to donate protons and it dissociates completely when dissolved in water.

Question 25

what does pH measure

Answer 25

the concentration of hydrogen ions in solution on a logarithmic scale

Question 26

in weak acids, how do you calculate pH

Answer 26

Ka = [H+] [A-] //// [HA] pH = -log[H+]

Question 27

what is pKa and what does the value of it suggest

Answer 27

-log10 Ka; useful when Ka is particularly small. The weaker the acid, the greater the value of pKa and the smaller the value for Ka

Question 28

what are the two assumptions involved in calculating pH for a weak acid

Answer 28

[H+] = [A-] at equilibrium because they have the same number of moles. Water is a second source of hydrogen ions but it produces a much lower number so does not cause significant inaccuracy by being neglected. Second assumption: [HA]init = [HA]eq This neglects the fraction of HA which has lost H+ because the fraction is very small.

Question 29

Kw is

Answer 29

the ionisation product of water and is used for the pH of a strong alkali

Question 30

what do buffers do

Answer 30

They maintain a constant pH when small amounts of acids/alkalis are added. Solutions of a weak acid and its corresponding salt or of a weak base and its corresponding salt.

Question 31

what are the assumptions involved in determining how buffers work

Answer 31

All the A- come from the salt (HA supplies very few due to weakness) Almost all the HA molecules put in the buffer solution remain unchanged

Question 32

adding acid to buffers

Answer 32

By adding protons, the concentration of H+ increases The extra H+ react with A- to make more HA and H+ are effectively removed This causes position of equilibrium to shift to the left pH is reestablished

Question 33

adding alkali to buffers

Answer 33

By adding OH-, concentration of H+ decreases The protons which were used up to react with the added hydroxides to form water are replaced when HA dissociates into H+ and A- This shifts the position of equilibrium to the right pH is reestablished

Question 34

equation for calculating pH of buffers

Answer 34

Ka = [H+] * [salt]////[acid] assuming A- conc and HA conc is equal to that of the salt and acid

Question 35

what is Ksp

Answer 35

the solubility product constant/ concentration of the ionic product at the threshold of solubility

Question 36

what does Ksp represent

Answer 36

the conditions for equilibrium between a sparingly soluble solid and its saturated solution

Question 37

if the ionic product is larger than Ksp..

Answer 37

a ppt will form

Question 38

if the ionic product is smaller than or equal to Ksp..

Answer 38

everything dissolves and there will be no ppt

Question 39

define entropy

Answer 39

the measure of the no of ways of arranging particles

Question 40

order of entropy in states and purity

Answer 40

gas > liquid > solid pure > solution > mixture

Question 41

factors to consider for signs of entropy changes ie positive or negative

Answer 41

Increase or decrease of product molecules Change in state i.e to solid or gas

Question 42

total S =

Answer 42

system S + surroundings S

Question 43

system S =

Answer 43

sum of S products + sum of S reactants

Question 44

surroundings S =

Answer 44

- enthalpy change of the system //// temp in K

Question 45

delta S =

Answer 45

overall changes in entropy

Question 46

when will a reaction occur spontaneously

Answer 46

if total S is positive and the activation enthalpy isn't too large

Question 47

what is 0

Answer 47

the threshold of spontaneity

Question 48

what does fewer gas molecules on the right of an exothermic reaction indicate

Answer 48

entropy of the system decreases and that of the surroundings increases

Question 49

how does lattice enthalpy change from F- to Cl-

Answer 49

size of the anion increases so the ions in the attract each other less strongly

Question 50

how does hydration enthalpy change from F- to Cl-

Answer 50

becomes less exothermic as the anion size increases and attracts water molecules less strongly

Question 51

explain the colour of phenolphthalein in alkali solutions

Answer 51

the equilibrium shifts right because the protons are removed by reaction with hydroxide ions so the indicator is present as In- which is pink

Question 52

acid is added to an ethanoate buffer

Answer 52

ethanoate ions from the salt react with protons to form more ethanoic acid and water so pH remains constant

Question 53

alkali is added to an ethanoate buffer

Answer 53

additions of hydroxide removes protons but these protons lost are replaced by more dissociation of ethanoic acid so pH remains the same