stuff

Question 1

reducing agents

Answer 1

fe3+ reduces with I-(orange brown to brown)
Cr2o72- reduces with Zn/H+
cu2+ reduces with I- (white ppt CuI and brown solution I2 2cu2+ +41-=2cui+i2

Question 2

oxidisng

Answer 2

cr3+ can be oxidised by hot alkaline H2O2 (yellow solution)
fe2+ by H+/mno4-(purple to pale pink

Question 3

disproportionation of cu+

Answer 3

brown solid cu and blue solution cuso4
cu2o+H2so4=cu+cuso4+h2o

Question 4

buffer formation

Answer 4

Propanoic acid reacts with sodium hydroxide
forming propanoate ions/sodium propanoate
propanoic acid AND propanoate (ions)/ sodium propanoate present equilibrium: CH3CH2COOH ⇌ H+ + CH3CH2COO–
CH3CH2COOH reacts with added alkali eq shifts right
CH3CH2COO– reacts with added acid eq shifts left

Question 5

fuel cells

Answer 5

converts energy from a reaction of a fuel with oxygen.
2h2+o2=2h20
hydrogen stored as a liquid or adsorbed onto a solid.energy needed to make the hydrogen

Question 6

why can a process be sponatenous even though it is endothermic

Answer 6

as disorder increases and T∆S > ∆H

Question 7

hydrogen fuel cells half equation

Answer 7

for o2=o2+4h20+4e-=4oh-
for h2=h2+2oh-=2h20+2e-

Question 8

enthalpy of hydration f- vs cl-

Answer 8

f- more negative(exothermic) as f- has a smaller ionic charge so greater attraction with water

Question 9

if you have negative kjmol what happens when you increase temperature

Answer 9

decreases solubility as enthalpy of solution is negative and equilibrium is displaceed as predicted by le chatelier

Question 10

2SO2(g)+O2(g)=2SO2(g) why does this exo reaction occur spontaneously at low temperatures but not high

Answer 10

as increasing temperature decreases TdeltaS
at low temperature deltaH-TdeltaS is less than zero

Question 11

why does cell potential change slowly over time

Answer 11

as concentration is not standard

Question 12

phenol vs benzene

Answer 12

lone pair on o is partially delocalised into pi ring electron density increases and cl2 is more polarised

Question 13

GC-MS

Answer 13

separate compounds and can be compared to a database

Question 14

combustion calculation

Answer 14

if temperature drops final value should be positive

Question 15

permanent dipoles

Answer 15

form when one atom more electronegative than other and dipoles don’t cancel out

Question 16

why is the evaporation of water spontaneous even though it is endothermic

Answer 16

as particles become more disordered
entropy increases so
enthalpy change is less than entropy times temperature and thus its less than 0

Question 17

optical isomers syntheses

Answer 17

use enzymes
use natural chiral molecules
this ensures single optical isomer

Question 18

increasing volume affect on buffer solution

Answer 18

PH is the same as the ratio of HA/A- is the same

Question 19

graph of ∆G = ∆H – T∆S

Answer 19

links to y=mx+c
gradient=-∆S
graph crosses y axis at ∆H
graph crosses x axis at temperature where feasibility changes

Question 20

purifying solids

Answer 20

Recrystallisation
 Dissolve impure solid in minimum volume of hot
water/solvent
 Cool solution and filter solid
 Wash with cold water/solvent and dry

Question 21

COOH electron withdrawing

Answer 21

electron-withdrawing so electron density is lower so less susceptible to electrophilic attack

Question 22

branching and compounds

Answer 22

Compound A (is branched so) has less points of contact /
less surface interaction between molecules 
Induced dipole–dipole forces are weaker.
AND
Require less energy to break (these interactions / forces)

Question 23

ice vs water

Answer 23

ice has hydrogen bonds.water forms 2 lone pairs and 2 bonded pairs lone pairs repel more than bonding pairs

Question 24

dynamic equilibrium

Answer 24

rate of the forward reaction is equal to the rate of the reverse reaction.the concentrations of the eactants and products remain constantbut are constantly interechanging

Question 25

why would a smaller concentration of acid be used in titration

Answer 25

smaller concentration gives a larger titre so smaller percentage uncertainty.

Question 26

why does molecule have no onverall dipole

Answer 26

one element more electronegative than other. molecule is symmetrical so dipoles cancel out

Question 27

why must acid be added so crystals of benzoate appear

Answer 27

as it protonates benzoate

Question 28

ifpurifyinging solids

Answer 28

dissolve in minimum volume of hot solvent.Cool and filter and dry.

Question 29

safety issues

Answer 29

toxic gas-use fume cupboard
compound toxic-use gloves
flammable-keep away from flame

Question 30

how to ensure whole reaction has occured

Answer 30

heat until mass remains constant
stir/break up solid to increase surface area
use excess

Question 31

how to identisy phenol

Answer 31

indicator paper turns red
no reaction with Na2CO3

Question 32

why cant e/z isomerism occur

Answer 32

as it would strain the ring

Question 33

kc effect if temp increases and reaction is exo

Answer 33

kc decrease as forward reaction is exothermic

Question 34

why is the reactant zero order

Answer 34

reactant is zero order as reactant is in excess

Question 35

benzene

Answer 35

p orbitals overlap to form pi bonds. Pi bonds are delocalised

Question 35

enthalpy change of hydration

Answer 35

enthalpy change when 1 mole of gaseous ions reacts.Gaseous ions dissolve in water

Question 36

increasing pressure effect on kp
2A+B=C

Answer 36

equilibrium shifts to the right .Ratio in kp decreases.The ratio in kp increases to restore kp

Question 37

weighted mean mass

Answer 37

is the mean mass taking into account the relative abundancies

Question 38

heterolytic fission

Answer 38

heterolytic-when one atom receives both electrons
fission-breaking of a covalent bond

Question 39

cdcl3 and d20

Answer 39

cdcl3 used as a solvent and d2o used to identify nh or oh groups via proton exchange

Question 40

why is experimental value less exothermic than actual

Answer 40

non standard conditions
heeat loss to surroundings
incomplete combustion