2024 paper 3 qs Flashcards
(27 cards)
Define relative isotopic mass (2)
Mass of an atom (of an isotope) (1)
Relative to 1/12th of the mass of a carbon 12 atom (1)
Deduce the number of peaks due to molecular ions H2+ in the mass spectrum of this sample (1)
5
2a) Explain how London forces arise (3)
Random movement/ uneven distribution of electrons (1)
resulting in a temporary/ instantaneous dipole (1)
which causes/induces a second dipole in a adjacent molecule (1)
Explain which of the compounds A-D will have the highest boiling temperature (2)
Compound A
as London forces increase as branching decreases /no branching (1)
so surface area and points of contact increases (1)
Explain whether or not each of these liquids will be deflected in this experiment (3)
Liquids; CCl4, CHCl3, C6H14
CHCl3 will be deflected (1) CCl4 and C6H14 won’t
Due to bond polarity in each of the three liquids (1)
Results in non-polar polarity due to CHCl3 being non-symmetrical (1)
Give a reason with reference to the filtration in step three why the formation of extremely small crystals in step two would lead to a lower mass of dry barium sulphate in step five (warm in dry oven) (1)
Crystals would be small enough to get through pores in filter paper
Explain why the crystals were rinsed in step 4 (with deionised water). (2)
To remove excess BaCl2 (aq) (1)
As it would crystallise and increase mass (of the Sulfate) (1)
What effect would placing the glass rod on the lavatory bench when stirring have on the calculated value of the RFM of M2SO4 (2)
Some M2SO4 would be lost (from beaker) (1)
So MOLES/AMOUNT would be less ANDcalculated formula mass would be higher (1)
Describe how the student should amend the procedure (not placing glass rod on bench while stirring) (1)
Rinse glass rod with the ionised water into the beaker
Explain what causes the flame colour in a flame test (2)
Heat causes electrons to be excited to a higher energy level (1)
light is admitted when electrons fall back to a lower level (1)
Give one advantage and one disadvantage of using a flame test to identify a metal cation rather than the method followed by the students in steps one to 5 (2)
Advantage
a simpler quicker process (1)
disadvantage
plain colours are subjective based on eyes //and some metal eyes produce very similar flame colours//and sometimes one or more colours maybe seen due to contamination (1)
Explain why calcium nitrate is less thermally stable than barium nitrate (3)
The calcium ion is smaller with higher charge density (1)
So Ca will polarise (anion) to a greater extent (1)
So weakens the N-O bond in nitrate (1)
Describe a test to confirm that ammonia has been produced (1)
Turns litmus paper blue
Compare and contrast the reactions of bromine with benzene and of bromine with cyclohexene
consider the types of reactions that occur the products that form and any special conditions that may be required 6 MARK
SIMILARITY
M1: Both reactions involve attacked by an electrophile .
DIFFERENCES
M2: Benzene reaction is a substitution. Cyclohexene reaction is in addition
M3: benzene forms Two products cyclohexane forms one product
M4: so benzene reaction requires a catalyst of FeBr3 to induce dipole in bromine
M5: cyclohexane react room temperature with bromine water
M6: benzene is less reactive, as electrons are localised across THE RING
Explain the expected splitting pattern for the peak due to proton environment are circled in the structure (2)
Singlet (1)
No adjacent carbon atoms with hydrogen atoms (1) - only bonded with oxygen in this case!
LABEL THE CH2 AND CH3 AS ENVIRONMENTS FOR THE NEXT Q !!!!!
Devise a reaction scheme for steps two and three of the synthesis include the answer or the agents and conditions the type of reaction in each step and the structure of A (5)
Structure a = CYCLOHEXANOL
M1: Bromocyclohexane with aqueous KOH
M2: nucleophilic substitution
M3: reflux or heat with sulfuric acid and sodium dichromate (VI) (or potassium if not sodium)
M4: oxidation
Explain why the anhydrous calcium chloride in tube X is necessary (2)
To prevent moist air entering (1)
as Grignard reagent will not form in presence of water/ avoid hydrolysis (1)
Describe how you would obtain pure crystals from the precipitate (4)
1) Solid dissolved in minimum amount of hot solvent
2) solution allowed to call and crystallise to form a precipitate
3) solid is filtered under reduced pressure
4) rinsed with cold solvent anddried between sheets of filter paper
Explain why this procedure will give invalid results when using ethanoic acid and a solution of an acid of unknown concentration (3)
Weak base titrated with a weak base (1)
No rapid change in pH (cannot find volume at the end point) (1)
End-point cannot be determined (1)
How should ammonia be replaced (as a base) to give valid results (1)
Use a strong base like NaOH/KOH
State a precaution you were taking carrying out step 3 justify your answer (2)
(boil the sample to remove any dissolved gases and allow it to cool )
- carry out in a fume cupboard (1)
- SO2 is toxic/poisonous (1)
Explain what effect the omission of step three would have on the titre (2)
SO2 form acids when dissolved (1)
Titre value would be greater (1)
The student carrying out the experiment forgot to remove an air bubble from the tip of the burette before carrying out a titration during the titration. The air bubble escaped.
explain the effect of this mistake would have on the value of this titre (2)
The titre value includes the volume of the air bubble
therefore the titre value would be greater than expected
