equillibria + acid base

Question 1

what is Le Chatelier’s principle

Answer 1

if a reaction at equilibrium is subjected to a change in pressure, temperature or concentration, the position of equilibrium will move to counteract the change

Question 2

what happens if you increase conc in homogenous reversible reaction

Answer 2

equillibrium will shift to try and reduce the conc (use up the increased conc)

Question 3

what happens if you increase pressure in homogenous reversible reaction

Answer 3

equilibrium will shift to try and reduce the pressure (shifts to side with fewest number of gas particles)

Question 4

what happens when you increase the temp in homogenous reversible reaction

Answer 4

equilibrium shifts to endothermic direction to reduce temp

Question 5

conditions for making ethanol

Answer 5

60atm pressure
300C temperature
phosphoric acid catalyst, H3PO4

Question 6

what is dynamic equilibrium

Answer 6

when both the rate of the forward and backward reaction are equal, the conc of reactants and products remain constant

Question 7

what do catalysts do to equilibrium

Answer 7

they affect forward and backward reaction equally, allowing equilibrium to be reached faster

Question 8

what states do we use in Kc expressions

Answer 8

aqueous + gases
only in homogenous equillibria

Question 9

what is the one thing that affects Kc

Answer 9

if temperature changes
if anything else shifts equillibria the conc of reactants and products stay in same ratio

Question 10

why does changing the concentration of a species not affect Kc

Answer 10

increasing 1 species will shift equilibrium to restore the conc to be proportional so same ratio of reactants and products are still in equilibrium

Question 11

how to work out Kc in opposite direction

Answer 11

1/ Kc for other reaction

Question 12

what is the partial pressure of a gas

Answer 12

the pressure the gas would exert if it alone occupied the volume of the mixture

Question 13

in exothermic reaction what happens to Kc/Kp when temp is increased

Answer 13

become smaller as position of equilibrium moves to the left so less products over reactants

Question 14

why do catalysts not affect Kp or Kc

Answer 14

they affect the rate of reaction but not the position of equilibrium, so they are only affecting how fast the system reaches equilibrium

Question 15

what is a Bronsted Lowry base

Answer 15

proton acceptor

Question 15

what is a Bronsted Lowry acid

Answer 15

proton donor

Question 16

what is a Bronsted Lowry conjugate acid

Answer 16

formed when a base accepts a proton

Question 17

what is a Bronsted Lowry conjugate base

Answer 17

formed when an acid donates a proton

Question 18

define pH

Answer 18

-log H+ concentration

Question 19

what is a strong acid

Answer 19

fully ionise (dissociate) to produce H+ ions when in solution in water

Question 20

what is a weak acid

Answer 20

partially ionise (dissociate) to produce H+ ions when in solution in water

Question 21

define pKa

Answer 21

-log Ka

Question 22

what does buffer solution mean

Answer 22

mixture of a weak acid and its salt that will resist changes in pH when small amounts of acid or alkali are added

Question 23

explain the use of blood being a buffer

Answer 23

carbon dioxide dissolved in the blood forms carbonic acid

so carbonic acid will shift right forming more H+ and hydrogencarbonate ions

large reservoir of hydrogencarbonate ions will react with H+ to restore pH

Question 24

why is the enthalpy of neutralisation less for weak acids

Answer 24

only partially dissociate/ionise some H+ are not free to react with OH- ions

Question 25

why are solids and liquids not in Kc expression

Answer 25

we assume that their concentrations remain constant

Question 26

whats total pressure

Answer 26

sum of all the pressures of the individual gases

Question 27

what affect does changing temperature have on Kp

Answer 27

if temperature change causes equilibrium to shift right then Kp will increase

Question 28

what is a polyprotic acid

Answer 28

an acid that donates more than one proton per molecule eg sulfuric

Question 29

why does H2O cancel out of Kw expression

Answer 29

we assume the conc of water remains constant as dissociates very weakly

Question 30

how do you calibrate pH meter

Answer 30

put it in distilled water, should read 7.0 repeat process with standard solutions of pH 4.0 and pH 10.0, rinse probe between them with water

Question 31

what assumptions do we make about weak acids and H+ in Ka expression

Answer 31

moles of HA at start = moles of HA equ conc H+ = conc A- (sometimes)

Question 32

what does the equivalence point on a titration curve show

Answer 32

the point during a titration at which the reactants have fully reacted (with acid/base titrations, where the mol of H+ = mol of OH-)

Question 33

what is the half equivalence point

Answer 33

the point during a titration where exactly half the reactant in the conical flask has been reacted

Question 34

what happens when you add acid to an acidic buffer

Answer 34

the H+ reacts with the high abundance of negative ions provided by the salt to produce more weak acid

Question 35

what happens when you add a base to an acidic buffer

Answer 35

OH- reacts with H+ so equillibrium shifts to restore lost H+ and pH doesn't fluctuate much

Question 36

what can acidic buffers be made from

Answer 36

weak acid and its salt excess weak acid and strong base

Question 37

what is a basic buffer

Answer 37

a weak base and its salt

Question 38

what happens when you add a base to a basic buffer

Answer 38

it reacts with large abundance of positive ions provided by the salt to create more weak base

Question 39

what happens when you add an acid to a basic buffer

Answer 39

reacts with OH- to create water, equillibrium shifts left to restore lost OH- therefore pH does not go down by a lot

Question 40

what is a closed system

Answer 40

one in which the reactants and products (or anything else) cannot leave or enter

Question 41

what is the buffer region of a pH curve

Answer 41

the region where pH only changes slightly as acid/alkali is added

Question 42

what is an indicator

Answer 42

weak acids where the protonated species and the deprotonated (salt) species have different colours