Chemistry Paper 2 Mistakes Flashcards
(36 cards)
Give one reason why ethanoyl chloride is not used in industrial synthesis
Vulnerable to hydrolysis
Corrosive
Dangerous to use
Explain how carbon dioxide causes global warming
C=O bonds in CO2 absorb infrared radiation.
Infrared radiation emitted by Earth does not escape from atmosphere
Suggest why aqeuous ethanol is a suitable solvent when heating the coconut oil with KOH
It dissolves both the oil and the KOH
State the meaning of fraction, as used in the term petrol fraction
A group of compounds with similar boiling points
Give a reason why carbon dioxide absorbs infrared radiation
It has polar C=O bonds
Suggest why Bioethanol is thought to be carbon neutral, giving relevant equations
Photosynthesis: 6CO2 + 6H2O → C6H12O6 + 6O2
Fermentation : C6H12O6 → 2C2H5OH + 2CO2
Combustion : 2C2H5OH + 6O2 → 4CO2 + 6H20
6 CO2 in and 6CO2 out
What are the environmental impacts of using bioethanol as an alternative to fossil fuels
Deforestation
Less land which can be used to grow crops and food.
Loss of biodiversity and habitats
Not carbon neutral as fuel is used in production and distribution
Give 2 disadvantages of using a glass beaker on a tripod and gauze instead of the clamped copper calorimeter
- Glass is a poorer conductor than copper
- Tripod and gauze reduce heat transfer
Suggest why chemists aim to design production methods with 1) fewer steps and 2.) high percentage atom economy
Fewer steps : Better yield
High percentage atom economy : Less waste
State how CFC’s form chlorine atoms in the upper atmosphere
C-Cl bonds broken
A student completed a series of experiments to determine the order of reaction.
Suggest why 1.0cm^3 portions of the reaction mixture are added to an excess of NaHCO3 solution
To neutralise the acid and so stops the reaction
Suggest when the order of the reaction with respect to a reactant can be ignored
When the concentration and amount of the reactant is much greater than the rest.
This means the concentration of this reactant remains constant.
Explain how the graph shows the reaction is zero order with respect to iodine in the reaction.
The gradient of the graph is constant and graph is a straight line.
The rate of reaction therefore does not change as the concentration of iodine changes
1,6-Diaminohexane can be formed in a 2 stage synthesis starting from 1,4-dibromobutane.
Suggest the reagent and a condition for each stage in this alternative synthesis
stage 1 : ethanolic KCN
stage 2 : H2/Ni
The cyclohexene separated from the aqeuous solution was obtained as a cloudy liquid. The student dried this cyclohexene by adding a few lumps of anhydrous calcium chloride and allowed the mixture to stand.
Give one observation that the student made to confirm the cyclohexene was dry
Liquid goes clear
Give reasons why ethanoyl anhydride is used instead of ethanoyl chloride in industrial synthesis
Vulnerable to hydrolysis
Corrosive
Dangerous to use
State why the dicarboxylic acid can be distinguished from the two diols by high resolution mass spectrometry using electrospray ionisation
The precise masses are different
Explain why NaBH4 reduces 2-methylbutanal but has no reaction with 2-methylbut-1-ene
The H- nucleophile attacks the delta positive carbon in 2-methylbutanal as it is attracted to it.
In 2-methylbut-1-ene there is a carbon-carbon double bond which is a region of high electron density which will repel the nucleophile.
Crude aspirin can be purified by recrystallisation using hot ethanol as the solvent.
Describe two important precautions when heating the mixture of ethanol and crude aspirin
- Use an electric heater to heat the mixture as ethanol is highly flammable
- Heat to temperature below boiling point of ethanol
State why Si(CH3)4 and CCl4 and CDCl3 are used in proton spectrometry and explain how their properties make them suitable for use in proton NMR spectrometry
CCl4 and CDCl3 are used as solvents.
CCl4 is not polar so is a good solvent for non-polar organic molecules
CDCl3 is polar so is a good solvent for polar organic compound.
They both do not contain any hydrogen atoms.
Si(CH3)4 is used to produce a reference peak at 0ppm.
It has a low boiling point so is easily removed from the sample.
It is inert
It only produces one signal far away to the right of all other peaks
Suggest why it is difficult to use Table B in the data booklet to predict the chemical shift for the peak given by the 4th H atom in CH3CHClCOCH(CH3)2
H is attached to both C-Cl and adjacent to C=O so does not fit with data in table B
Why is the reaction of water with ethanal slower than the reaction between chloroethanal and water
The CH3 is electron donating and has a positive inductive effect / Cl has negative inductive effect.
The carbon attacked in chloroethanal is more delta positive and so stronger attraction between delta positive carbon and the nucleophile
Give the catalyst and conditions needed for the catalytic cracking of hexadecane
Zeolite catalyst
High temperature, moderate pressure
Why is the halogenoalkane CH2(OH)CH(CH3)CH2Br attacked by the nucleophile, OH-
The halogenoalkane has a polar C-Br bond so the nucleophile is attracted to the delta positive carbon and attacks it. The carbon of the C-Br bond is delta positive since the bromine atom is more electronegative than carbon. Lone pair on nucleophile is donated to and attacks the partially positive carbon.
