chem eoy corrections

orbitals

1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6

chromium electronic configuration

1s2 2s2 2p6 3s2 3p6 3d5 4s1

copper electronic configuration

1s2 2s2 2p6 3s2 3p6 3d10 4s1

trend in boiling temperatures of isomers

increasing number of side groups lower boiling temperature

solvation of ionic compounds (in water)

ions hydrated

• δ− oxygens point towards lattice cations

• δ+ hydrogens point towards the lattice anions

• ion-dipole interactions provide enough energy to pull ions away from the lattice

• as each ion is released it becomes surrounded by a ‘shell’ of water molecules

• enthalpy changes:

  • breaking apart the lattice is endothermic, requiring energy to overcome lattice enthalpy

  • forming ion-water interactions releases energy (hydration enthalpy)

reasons for chlorine mass spec peaks at 70, 72, 74

three possible combos: Cl35Cl35, Cl35Cl37, Cl37Cl37

disproportionation reaction

one species is both reduced and oxidised

thermometric titration - temp increase/decrease after endpoint

• extra titre cooled the mixture as was colder than solution (or reverse argument)

• equilibrated to room temp

drying agents - core prac 6: chlorination of 2methyl-prop-2-anol

anhydrous CaCl2, MgSO4, Na2SO4

chemical tests vs IR spectroscopy

• chemical tests: cheap, accessible

• IR spec: more sensitive

gas collection

when collecting a gas that is highly soluble in water, a syringe must be used instead of water displacement

standard solution

a solution with a precisely known concentration, measured to 3dp to reduce the impact of measurement uncertainties

% uncertainty

uncertainty/measurement * 100%

% error

| (experimental - theoretical)/theoretical | * 100%

concordant titres

within ± 10cm³

primary standard properties

• high purity

• stable - must not react with air (eg absorb water or CO2) so its mass does not change over time

• high molar mass - reduces weighing errors as small weighing inaccuracies have less effect

• soluble in water - must dissolve completely to make a solution of known concentration

problem with making up standard solutions using hot distilled water

• high temp = particles with more KE

• moles of solute remains constant, vol liquid decreases (as it cools)

• concentration of solution increases

volumetric flask to be rinsed with distilled water only

does not affect moles of solute added

max accuracy and precision in method for making up standard solution

• measure all masses to 3dp

• measure mass of container with solid, and then after emptying

• add beaker, stirring rod and funnel washings into volumetric flask

• invert flask ~20 times to ensure homogenisation of solute concentration

burette reading uncertainty

uncertainty * 2 because two readings are taken to find a titre volume

leaving funnel in burette decreases experimental validity

introduces random error, due to the random volume and timing of excess drop down the burette during the course of the titration, affecting the volume measured

bubble in jet of the burette

air bubble would take up space, meaning volume recorded by the burette is higher than the true volume, therefore moles of HCl added would be less than the accurate value, meaning the calculated concentration will be too high

nucleophile species in hydrolysis of haloalkanes - core prac 4

• water is the nucleophile - contains two lone pairs that can attack (attracted to positive parts of other molecules)

• in this experiment, the carbon is slightly positive (δ⁺) because the halogen pulls electrons away from it

• water uses one of its lone pairs to form a new bond to the carbon atom

• pushes the halogen out (leaving it as a halide ion)

• water molecule attaches to the carbon and is deprotonated, forming H3O+ ion with another water molecules in solution

why is ethanol - core prac 4

haloalkanes are not very water-soluble because they are not very polar, therefore ethanol used as a solvent

nucleophilic substitution of primary haloalkanes

• Sn2 mechanism - one-step process with a transition state where the nucleophile attacks the carbon at the same time as the halide leaves

• primary haloalkanes only have one alkyl group meaning the nucleophile can attack the carbon from the opposite side of the halogen

• because both nucleophile and haloalkane are involved in the slow (rate-determining) step, this is Sn2 - bimolecular mechanism

nucleophilic substitution of tertiary haloalkanes

• Sn1 mechanism - two-step process where halide leaves to form carbocation intermediate, then the nucleophile attacks the carbocation