Exam Improvements Flashcards
Which element reacts with water to give a solution that can begave as an oxidising agent?
Chlorine
What colour compounds do group 2 compounds form?
Colourless (NOT DULL)
What is a use for barium sulfate?
In medicine to produce an x-ray image
Which of the following is not a nucleophile?
HBr
rate = k[W][X]²
Reaction 1 = Reduced
Reaction 2 = Oxidised
Reaction 3 = Disproportionates
Ammonia reacts with nitrogen oxides to form harmless products. Write the equation for the reaction between ammonia and nitrogen monoxide, NO.
A chemist performed the reaction “2SO₂(g) + O₂(g) ⇌ 2SO₃(g)” with 1.00 mol SO₂ and 0.5 mol O₂. They repeated the experiment at the same temperature with 1.00 mol SO₂ and an excess of O₂. The gas mixture was compressed to the same volume as previously.
State and explain, in terms of Kc, how the equilibrium yield of SO₃ would be different from the yield in the first experiment:
Adding an excess of O₂ causes the pressure to increase, however, Kc does not change with pressure. As more O₂ has been added, the concentration of O₂ increases. Therefore, the denominator of the Kc expression increases causing the value of the expression to differ from that of Kc. As a result more SO₃ is produced to increase the numerator and restore the value of Kc.
Therefore the equilibrium yield of SO₃ increases
Write the equation for the first ionisation energy of iron
Fe(g) -> Fe⁺(g) + e⁻
What state is Iodine at room temperature and pressure?
solid
What state is Bromine at room temperature and pressure?
liquid
What state is Chlorine at room temperature and pressure?
gas
What is the electron configuration for Fe²⁺
1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁶
Predict the products of Fe(s) reacting separately with I₂(aq), Br₂(aq) and Cl₂(aq)
- Iron will react with Cl₂ to form FeCl₂ and FeCl₃ as +1.36V > -0.44V and +0.77V
- Iron will react with Br₂ to form FeBr₂ and FeBr₃ as 1.09V > -0.44V and +0.77V
- Iron will react with I₂ to form FeI₂ only. This is because +0.54V > -0.44V so iodine can be reduced and iron can be oxidised to Fe²⁺. However, they cannot form FeI₃ as +0.77V > +0.54V and therefore Iodine cannot oxidise Fe²⁺ to Fe³⁺
What is the advantage of using ethanoic anhydride instead of ethanoyl chloride duignt eh manufacture of aspirin?
Ethanoic anhydride is less corrosive
Draw the structure of the product of this reaction
What should you add to a solution of this compound to form benzoic acid?
HCl
Why in the recrystallisation process, must you use the minimum volume of hot solvent when dissolving the product?
To obtain a saturated solution and reduce the amount of product left in solution. This enables recrystallisation on cooling
Why in the recrystallisation process, must you filter the hot solution?
You must filter the solution to remove insoluble impurities, and it must be hot to prevent crystals forming during the filtration process
Why in the recrystallisation process, must you cool the filtrate in an ice bath?
You must cool the solution to decrease the solubility of the solid, allowing crystals to form and for you to obtain more crystals
Why in the recrystallisation process, must you filter of the crystals and wash them with a cold solvent?
To remove soluble impurities
What are 2 advantages of filtration under reduced pressure (Method B) over traditional filtration (method A)?
- Filtration is quicker
- Product is drier
- Melting point lower than the correct value
- Melts over a wide range of temperatures
Why does methylbenzene not react easily with nucleophiles (such as ammonia)?
The delocalised ring of electrons within benzene is electron rich, therefore it repels nucleophiles
In proton NMR, a peak at δ = 4.2ppm is further downfield than the other peaks, what causes this shift?
It is deshielded compared to the others as it may be close to an electronegative atom (such as oxygen)
In proton NMR, a peak at δ = 1.3ppm is split into a triplet, what does this tell us about the structure of the molecule?
The molecules contains a CH₂ group
What does it tell you about the structure of a compound if it does not react with acidified sodium dichromate?
- It does not contain a primary or secondary alcohol group
- It does not contain an aldehyde group
What does it tell you about the structure of a compound if it reacts with an aqueous acid, forming ethanol as one of the products?
An ester group is present
Determine the skeletal structure of compound X:
* Compound X has the molecular formula C₇H₁₂O₄
* It does not react with acidified sodium dichromate (VI)
* It reacts with an aqueous acid, forming ethanol as one of the products
* In the mass spectrum of compound X it forms a fragment peak at m/z = 131
* The proton NMR results are shown below:
IMPORTANT
ONLY 1 and 2
Why doesn’t SiO₂ experience London forces?
Silicon Dioxide has a giant covalent structure, therefore it does not contain small individual molecules and therefore does not contain London forces (as they act between molecules)
Calculate the ratio of C₆H₇O₆⁻ to C₆H₈O₆ and hence the mass of C₆H₇O₆Na in the low acidity vitamin C tablet
pKa of solution = 4.17
- C₆H₇O₆⁻ : C₆H₈O₆ = 0.708 : 1
- C₆H₇O₆Na = 239mg
REMEMBER TO BALANCE CHARGES ASWELL AS ELEMENTS
What must you remember when balancing redox/ionic equations?
The charges must also be balanced! (not just the elements)
MnO₄²⁻(aq) ions disproportionate under acidic conditions in the below equation. MnO₄²⁻(aq) ions are stable under alkaline conditions. Explain this difference in terms of equilibrium
- In acidic conditions, the concentration of H⁺ increases and equilibrium shifts to the right to reduce the concentration of H⁺
- In alkaline conditions, the OH⁻ reacts with H⁺ and the equilibrium shifts to the left to increase the concentration of H⁺
-
Acidic:
Oxidation: H₂(g) ⇌ 2H⁺(aq) + 2e⁻ E° = 0V
Reduction: O₂(g) + 4H⁺(aq) + 4e⁻ ⇌ 2H₂O(l) E° = +1.23V
Overall equation: O₂(g) + 2H₂(g) ⇌ 2H₂O(l)
Total e.m.f: 0 + 1.23 = +1.23V -
Alkaline:
Oxidation: 2OH⁻(aq) + H₂(g) ⇌ 2H₂O(l) + 2e⁻ E° = -0.83V
Reduction: O₂(g) + 2H₂O(l) + 4e⁻ ⇌ 4OH⁻(aq) E° = +0.40V
Overall equation: O₂(g) + 2H₂(g) ⇌ 2H₂O(l)
Total e.m.f: 0.83 + 0.4 = +1.23V
Identify the colour at the end point of this titration
Colourless to pale pink
Mn²⁺ is colourless, but once the reaction has stopped, purple MnO₄⁻ will not be reduced to Mn²⁺ and will remain in the solution. Therefore, at the end point the solution will change from colourless to a pale pink
The student uses the following method for the titration with reaction “MnO₄⁻(aq) + 8H⁺(aq) + 5Fe²⁺ -> Mn²⁺(aq) + 4H₂O(l) + 5Fe³⁺”. Explain the importance of step 1 and 2
1. The zinc will be oxidised and reduce Fe³⁺ to Fe²⁺. This is possible as -0.76 < + 0.77 and so the zinc will reduce Fe³⁺ to Fe²⁺. This allows the combined concentration of Fe³⁺ and Fe²⁺ to be determines as Fe³⁺ has been reduced to Fe²⁺
2. Excess zinc is removed as it may be oxidised by MnO₄⁻ and in turn reduce the MnO₄⁻ to Mn²⁺. This would increase the average titre as more MnO₄⁻ would need to be added to oxidise all of the zinc and Fe²⁺. Therefore it is removed as to not affect the results. This is possible as -0.76 < +1.51 and therefore the redox reaction can occur
What is the bond angle in a trigonal planar molecule?
120°
What is the reaction between an alcohol and a metal?
alcohols behave as an acid, forming salt + hydrogen
What is the most important thing to remember when identifying fragment peaks?
THEY ARE IONS. Do not forget to put the charges on the fragments!
**INCREDIBLY IMPORTANT **
Draw the displayed formula of an unbranched position isomer of pentan-2-ol that can be dehydrated to form a single alkene
Draw an isomer of pentan-2-ol that is not dehydrated when heated with concentrated sulfuric acid
