Paper 3 Mistakes Flashcards
Why do unbranded compounds have highest boiling temp?
More London forces as there is less branching
- so surface area increases/points of contact increase
Out of CCl4 , CHCl3 and C6H14, which would be deflected by a charged rod?
CHCl3 deflected only
CHCl3 has polar bonds
As it’s non symmetrical
Experiment to identify group I metal ion in a sulfate:
Why would formation of very small crystals lead to lower mass of dry barium sulfate ?
Crystals are small enough to get through filter paper
Experiment to identify group I metal ion in a sulfate:
Why are crystals rinsed?
Remove excess BaCl2/MCl (this was added in excess earlier on)
Which would otherwise crystallise
What causes the flame colour in flame tests?
Electrons are promoted and THEN
Electrons move down to lower energy levels emitting energy in form of light
Bromination of benzene/cyclohexene reaction?
BENZENE: substitution reaction
Cyclohexene: addition reaction
Cyclohexene also reacts at room temp and with bromine water
Reaction to form CH3CH2MgBr requires bromoethane + magnesium to be warmed under reflux with suitable solvent:
Explain why anhydrous calcium chloride in tube X (tube above reflux condenser) is necessary ?
Prevent moist air entering as gignard reagent will not form in presence of water
Why does the water from condenser flow in from direction shown of diagram (from bottom of condenser)?
Ensure efficient cooling /prevent air bubbles forming in condenser
What type of base is ammonia?
Weak base
Acidity in wine is due to dicarboxylic acid tartaric acid C4H6O6
SO2 added to wine - conc of tartaric acid and SO2 in wine can be determined by titrations
To find total amount of tartaric acid :
One of steps include BOILING SMAPLE TO REMOVE DISSOLVED GASES AND ALLOW TO COOL.
I. State the precaution to carry this out ?
II. What affect would it have on titre if this step was not included?
I. Carry out in fume cupboard
SO2 is toxic
II. SO2 forms acids when dissolved so titre value will be greater
How does the addition of sodium hydrogen carbonate reduce loss of SO2 from flask ?
Produce CO2
Which forms blanket/layer on surface of solution
Ethyl ethanoate + water with HCL catalyst followed using titrimetric method :
I. Why is the mixture added to crushed ice?
II. Why is remaining reaction mixture heated under reflux after an hour before titrating again with NaOH?
I. Quench the reaction
To allow time for the titration to be carried out
II. Ensure hydrolysis / reaction reaches equilibrium so max amount of carboxylic acid formed can be determined
