stuff Flashcards
reducing agents
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
oxidisng
cr3+ can be oxidised by hot alkaline H2O2 (yellow solution)
fe2+ by H+/mno4-(purple to pale pink
disproportionation of cu+
brown solid cu and blue solution cuso4
cu2o+H2so4=cu+cuso4+h2o
buffer formation
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
fuel cells
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
why can a process be sponatenous even though it is endothermic
as disorder increases and T∆S > ∆H
hydrogen fuel cells half equation
for o2=o2+4h20+4e-=4oh-
for h2=h2+2oh-=2h20+2e-
enthalpy of hydration f- vs cl-
f- more negative(exothermic) as f- has a smaller ionic charge so greater attraction with water
if you have negative kjmol what happens when you increase temperature
decreases solubility as enthalpy of solution is negative and equilibrium is displaceed as predicted by le chatelier
2SO2(g)+O2(g)=2SO2(g) why does this exo reaction occur spontaneously at low temperatures but not high
as increasing temperature decreases TdeltaS
at low temperature deltaH-TdeltaS is less than zero
why does cell potential change slowly over time
as concentration is not standard
phenol vs benzene
lone pair on o is partially delocalised into pi ring electron density increases and cl2 is more polarised
GC-MS
separate compounds and can be compared to a database
combustion calculation
if temperature drops final value should be positive
permanent dipoles
form when one atom more electronegative than other and dipoles don’t cancel out
why is the evaporation of water spontaneous even though it is endothermic
as particles become more disordered
entropy increases so
enthalpy change is less than entropy times temperature and thus its less than 0
optical isomers syntheses
use enzymes
use natural chiral molecules
this ensures single optical isomer
increasing volume affect on buffer solution
PH is the same as the ratio of HA/A- is the same
graph of ∆G = ∆H – T∆S
links to y=mx+c
gradient=-∆S
graph crosses y axis at ∆H
graph crosses x axis at temperature where feasibility changes
purifying solids
Recrystallisation
Dissolve impure solid in minimum volume of hot
water/solvent
Cool solution and filter solid
Wash with cold water/solvent and dry
COOH electron withdrawing
electron-withdrawing so electron density is lower so less susceptible to electrophilic attack
branching and compounds
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)
ice vs water
ice has hydrogen bonds.water forms 2 lone pairs and 2 bonded pairs lone pairs repel more than bonding pairs
dynamic equilibrium
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
why would a smaller concentration of acid be used in titration
smaller concentration gives a larger titre so smaller percentage uncertainty.
why does molecule have no onverall dipole
one element more electronegative than other. molecule is symmetrical so dipoles cancel out
why must acid be added so crystals of benzoate appear
as it protonates benzoate
ifpurifyinging solids
dissolve in minimum volume of hot solvent.Cool and filter and dry.
safety issues
toxic gas-use fume cupboard
compound toxic-use gloves
flammable-keep away from flame
how to ensure whole reaction has occured
heat until mass remains constant
stir/break up solid to increase surface area
use excess
how to identisy phenol
indicator paper turns red
no reaction with Na2CO3
why cant e/z isomerism occur
as it would strain the ring
kc effect if temp increases and reaction is exo
kc decrease as forward reaction is exothermic
why is the reactant zero order
reactant is zero order as reactant is in excess
benzene
p orbitals overlap to form pi bonds. Pi bonds are delocalised
enthalpy change of hydration
enthalpy change when 1 mole of gaseous ions reacts.Gaseous ions dissolve in water
increasing pressure effect on kp
2A+B=C
equilibrium shifts to the right .Ratio in kp decreases.The ratio in kp increases to restore kp
weighted mean mass
is the mean mass taking into account the relative abundancies
heterolytic fission
heterolytic-when one atom receives both electrons
fission-breaking of a covalent bond
cdcl3 and d20
cdcl3 used as a solvent and d2o used to identify nh or oh groups via proton exchange
why is experimental value less exothermic than actual
non standard conditions
heeat loss to surroundings
incomplete combustion
