Chemistry Paper 2 Flashcards
Suggest how the student calculated the temperature values in table 1
Measure the temperature at the start and end of the reaction and find the mean
Explain why a small increase in temperature causes a large increase in the rate of a reaction
- Many more particles have activation energy
- More successful collisions
A student has samples of these four compounds but does not know which is which:
butanoic acid
2-methylpropanal
2-methylpropanoic acid
2-methylpropan-1-ol
Step 1: Two of these compounds can be identified by simple chemical tests.
Step 2:
The other two compounds, that contain the same functional group as each other, can then be distinguished using a spectroscopic technique.
Describe how these two steps could be used to identify which compound is which
Stage 1:
2-methylpropanal
Tollens reagent
Silver mirror
Stage 2:
2-methylpropan-1-ol
Acidified K2Cr2O7
Orange to green
Stage 3:
Distinguishing the acids
Use IR spectroscopy to distinguish the two acids
Use finger-print region of IR spectrum
Look for exact match to spectra of known compounds
What is a positional isomer of hex-2-ene
hex-3-ene
There is a very low yield of butan-1-ol from but-1-ene. Explain why
- Formed from a less stable carbocation
- Formed from primary rather than secondary carbocation
What is the x and y axis on the Maxwell-Boltzmann distribution curve?
X axis -> energy
Y axis -> number of molecules
Why does the Maxwell-Boltzmann distribution curve start at the origin?
There are no molecules with zero energy
Why does the highest peak in the Maxwell-Boltzmann distribution curve represent?
The most probable energy
Name the mechanism for a reaction with cyclohexene and Br2
Electrophilic addition
Explain why there is an attraction between a C=C double bond and Br2
- C=C double bond is electron rich
- Br–Br bond becomes polarised
- S+ attracted to C=C
Propanone can be made by reacting propan-2-ol with an excess of acidified potassium dichromate (VI).
The propanone is removed from the reaction mixture by distillation.
Figure 2 shows the apparatus set up by a student to make propanone by this method. Suitable clamps are used to hold all the apparatus firmly in place.
There are three problems with the apparatus set up in Figure 2.
For each problem:
identify the problem
describe the issue it would cause
suggest how the problem can be solved
Stage 1:
No anti-bumping granules
Prevents formation of large bubbles
Add ABG
Stage 2:
Open system with no thermometer
System should be closed (above flask) to prevent gases from escaping
Should be closed with bung and thermometer
To allow collection of only propanone
Stage 3:
The water direction in the condenser
Water flows in the wrong direction through condenser
The condenser is not cool enough
Product may not condense
Explain why propanone has a lower BP than propan-2-ol
- Propanone has I.D.D forces
- Propan-2-ol has HB between molecules
- Propan-2-ol has stronger intermolecular forces
The molecule CFC-11 was commonly used as a refrigerant.
Use IUPAC rules to name CFC-11
Trichlorofluromethane
State the benefit to life on Earth of ozone in the upper atmosphere
Absorbs UV light
Suggest one reason as to why the use of CFCs was not restricted until seven years later
Lack of alternatives to CFCs
CFC-11 is a greenhouse gas that can contribute to global warming.
State and explain how CFC-11 is able to contribute to global warming
- Absorbs infrared radiation
- Molecule has polar bonds
This question is about poly(propene).
The three key steps in the manufacture of poly(propene) from crude oil are shown.
Naphtha is a mixture of alkanes with 6 to 12 carbon atoms per molecule.
For each step, name the process and state briefly the purpose of the process that leads to the formation of poly(propene).
Step 1:
Fractional distillation
Separated into mixtures of compounds with similar boiling points
Step 2:
Thermal cracking
To make alkenes
Step 3:
Addition polymerisation
Molecules joined together or to produce long chain molecule
Poly (propene) is not biodegradable because it is unreactive.
Explain why poly(propene) is unreactive
Non-polar
Scientists are developing new polymers, including some that are biodegradable.
Suggest why it is beneficial for some polymers to be biodegradable
To prevent the build up of waste
Prop-2-en-1-ol can be prepared by reacting 3-chloroprop-1-ene with dilute aqueous sodium hydroxide.
Name the mechanism for this reaction
Nucleophilic substitution
Define enthalpy change
Change in heat energy at a constant pressure
Explain why the value given for the O=O bond enthalpy is not a mean value
O2 is the only substance that has O=O bond
Electronegativity definition
The relative tendency of an atom to attract a pair of electrons in a covalent bond
Deduce two atoms the will form the most polar bond
H and O
