as 2024 questions Flashcards
Observation when 3 drops
of bromine water are added
Solution P Orange solution
Solution Q Brown solution
Solution R Orange solution
Water Orange solution
Identify the halide ion present in Q.
Give the ionic equation for the reaction that occurs when bromine water is added to Q.
Iodide ion / I–
Br2 + 2 I–
→ I2 + 2 Br–
Observation when 3 drops
of bromine water are added
Solution P Orange solution
Solution Q Brown solution
Solution R Orange solution
Water Orange solution
Explain, in terms of oxidising ability, why the observations from these reactions
do not allow the student to identify the halide ion present in P and the halide ion
present in R.
Bromine not a strong enough oxidising agent to displace chlorine (so
no visible change will be observed)
Bromine not a strong enough oxidising agent to displace bromine (so
no visible change will be observed)
1.3 The student adds a few drops of aqueous silver nitrate solution to
2 cm3 of each potassium halide solution.
Describe a further chemical test that the student can complete on the precipitates
formed to identify the halide ion present in P and the halide ion present in R.
Describe how the observations from this test can be used to identify the halide ion
present in P and the halide ion present in R
Add dilute ammonia
The precipitate containing chloride ions will dissolve/react to form a
colourless solution
The precipitate containing bromide ions will show no visible change
2.1. This question is about the elements in Group 2.
Explain why the third ionisation energy of beryllium is much higher than the
second ionisation energy of beryllium.
Electron is removed from 1(s) (rather than 2(s))
Lower in energy (than 2s) / Less/No shielding / closer to the nucleus
Stronger attraction between nucleus and outer electron
2.2 Magnesium reacts slowly with cold water but rapidly with steam.
Compare these reactions, in terms of the products formed.
You should identify one similarity in, and one difference between, these reactions
Similarity: produce hydrogen / produce gas / produce white solids /
produce Mg2+ compounds / produce a base
Difference: magnesium oxide formed with steam and
magnesium hydroxide formed with (cold) water
2.3. The reaction of calcium with water is a redox reaction.
Explain, in terms of oxidation states, why this reaction involves both oxidation
and reduction
Oxidation state of Ca increases, so Ca is oxidised
Oxidation state of H decreases, so H is reduced
3.1. Define electronegativity.
The (relative) ability of an atom to attract electron density in a
covalent bond
3.2. Explain why the C–Cl bond is polar.
Chlorine has a higher electronegativity (than carbon)
So the electron density is unsymmetrical / so chlorine becomes δ–
and carbon becomes δ+
3.3. Although the C–Cl bond is polar, CCl4 is a non-polar molecule.
Explain why
CCl4 is (a) symmetrical (molecule) / is tetrahedral / there is an even
distribution of electron density
So the dipoles cancel out
3.4. There are van der Waals forces between non-polar molecules.
Explain what causes these forces
(Random) movement of electrons (in one molecule creates a dipole) /
a temporary dipole is formed (in one molecule) / an imbalance in
electron density (in one molecule)
Induces a dipole in another molecule
(These temporary) dipoles in different molecules attract / (temporary)
attraction between δ+ and δ– in different molecules
- A student is provided with separate unlabelled samples of four different solutions
for analysis.
The four solutions are known to be ammonium nitrate, potassium sulfate,
sodium carbonate and magnesium nitrate, but the student does not know which
sample is which.
Outline a series of test-tube reactions that the student can use to identify each of
these solutions.
Include:
* the expected observations
* ionic equations for any reactions.
1a: add NaOH
1b: add NaOH (and warm) then hold damp red litmus
at mouth of tube (if sequential tests performed NaOH
can be scored from 1a)
1c: add nitric acid / hydrochloric acid
1d: add acidified BaCl2 / acidified Ba(NO3)
2a: Mg2+/Mg(NO3)2 will give a white ppt with NaOH
2b: red litmus (at mouth of the tube) will turn blue for
NH4
+/NH4NO3 with NaOH
2c: CO32–/Na2CO3 will effervesce with acid / gas
formed turns limewater cloudy
2d: SO42–/K2SO4 will give a white ppt with BaCl2
2e: the final tube will be the remaining solution (if only
three tests have been done).
- SF6 and SF3
+ have different shapes and different bond angles.
Deduce the shape of SF6 and the shape of SF3
+
State the bond angle in SF6 and the bond angle in SF3
+
Justify the bond angles by referring to electron pairs.
M1: SF6 is octahedral (either in words or as a structure)
M2: SF6 bond angle is 90°
M3: SF6 all the bond pairs repel equally
M4: SF3
+ is (trigonal) pyramidal (either in words or as a structure)
M5: SF3
+ bond angle is 103-107°
M6: SF3
+ lone pair-bond pair repulsion is greater than bond pair-bond
pair repulsion (so bond angle is reduced
6.2. A sample of bromine (Br2) is analysed in a mass spectrometer.
The sample is ionised using electron impact ionisation.
Give an equation, including state symbols, for the process that occurs during the
ionisation of bromine.
Br2(g) → Br2+ (g) + e–
6.4. State how the detector enables the relative abundance of each ion to be determined.
The (relative) abundance is proportional to the size of the current.
8.1 Define standard enthalpy of formation
The enthalpy change when one mole of a substance is formed from
its (constituent) elements.
All substances in their standard states (at 100 kPa and a stated
temperature
