paper 2 chem

additional instructions to increase accuracy of titration

weighing by difference
rinse beaker and add washings to graduated flask
invert flask several times to ensure uniform solution
use a funnel to transfer to the flask and rinse the funnel
use a stirrer to prepare solution and rinse the stirrer

describe briefly how you would ensure that a reading from a pH meter is accurate

calibrate using solutions of known pH, plot a calibration curve

what would result in a decrease in the pH of an aqueous solution of the acid (HA → A- + H+ )

dissolving some of the salt NaA in the solution

explain why hyrdation enthalpy of flouride ion is more negative than the hydration enthalpy of the chloride ion

flouride ion is smaller, so greater attraction to delta positive H in water molecule

explian why dissolving silver chloride in water is always a spontaneous process

as the entropy change is always positive and the enthalpy change is always negative, so value of delta G will always be negative

explain why the entropy value for nitrogen is higher than the entropy value for graphite

nitrogen is a gas, whilst graphite is a solid
particles more disordered

after temperatures higher than the temperature at which a reaction becomes feasible, why does this reaction not occur in a car exhaust in the absence of a catalyst

high activation energy

explain the term perfect ionic model

ions perfectly spherical, with no covalent interaction

explain interactions between water molecules and flouride ions when the flouride ions become hydrated

F- is attracted to the delta positive H
as water is polar

explain why this reaction does not occur at very high temperatures even though the reaction is exothermic (3)

2SO2 + O2 → SO3 (reversible)

3 moles of gas are forming 2 moles of gas

so entropy change will always be negative

high temperatures mean that TAS > deltaH so deltaG is positive

write an equation for the complete combustion of methanol, explain why the combustion reaction in the gas phase is always feasible

combustion is always exothermic, so deltaH always negative
2.5 mol of gases become 3 mol gases so deltaS always positive
so deltaG always negative

describe two ways the bp would show the product is impure

lower than data book value
would melt over a range of values

describe recrystallisation process to produce aspirin

1- dissolve in minimum volume of hot solvent
2- filter whilst hot to remove
3- let crystals cool to recrystalise
4- suction filtration with buchner flask and filter paper
5- wash with cold solvent to remove soluble impurities
6- pat crystals dry

why is it better to have fewer steps in a reaction

less energy/ higher yield

why is it important to have high percentage atom economy

lower waste

suggest how the anti-bumping granules prevent bumping during reflux

prevents large bubbles from forming

suggest why reflux s not essential when the flask is heated to 85 degrees

boiling point above 85 degrees

describe what you would observe when magnesium burns in oxygen

white flame, white solid, smoke

describe what you would observe when sulfur burns in oxygen

blue flame and choking gas

explain why sodium oxide reacts to form an alkaline solution

O2- reacts with water to form OH- ions

structure of nylon 6,6

CO(CH2)4CONH(CH2)6NH

monomers of kevlar

benzene 1, 4 dicarboxylic acid
1,4 diamino benzene

intermolecular forces between polyester chains

van de Waals
dipole-dipole

polyamide forces between chains

van de Waals
dipole-dipole
H bonds between H on the NH on one chain and the lone pair on CO of an adjacent chain

why do addition polymers not decompose

inert, strong C-H chain, non-polar so cant be hydrolysed or attacked by a nucelophile

what is the isoelectric point

pH at which the overall charge is zero

what bonding in solid amino acids

exist as zwitterions
ionic bonding

melting points of amino acids

high

what happens to amino acid in high pH

H+ lost from COOH group to COO-

what happens to amino acid in low pH

H+ gained on NH2 group to form NH3+

uses of PET

plastic bottles

uses of nylon

fabrics and rope

uses of kevlar

bullet proof vests

how many H2O in formation of condensation polymer

2n-1