topic 6 - organic Flashcards
what is meant by the term stereoisomers
compounds with the same structural formula where the atoms have a different arrangement in space
explain why different alkanes in crude oil can be separated by fractional distillation
- different alkanes have different boiling points
- because of different chain lengths
why is nucleophilic substitution with potassium cyanide particularly useful in organic chemistry
- increases the number of carbon atoms in the carbon chain/ increases length of carbon chain
explain why in nucleophilic substitution using potassium cyanide, the reactants are heated in a sealed container
- heating increases the rate of reaction
- no sealed tube would result in loss of ammonia gas
suggest a reason why oil companies reform alkanes such as heptane
- more efficient combustion
- allows smoother burning
- more efficient fuel
explain why the general formula of alkanes are different to the general formula of cycloalkanes
- general formula of cycloalkane is the same as alkenes (CnH2n) whilst alkanes are CnH2n+2
- alkenes have a double bond with 2 less carbons
- cycloalkanes have carbons in a ring resulting in 2 less hydrogens
halogenoalkanes practical: give a reason for the addition of ethanol to each test tube
- to increase the solubility of halogenoalkane
halogenoalkanes practical: give a reason why the test tubes were left in the water bath for 5 minutes before adding the halogenoalkanes
- to allow the solutions to reach the same temperature (50)
- to allow the solutions to equilibrate
halogenalkanes practical : explain why halide ions are present in the mixture containing halogenoalkanes which only has covalent bonds
- halogenoalkane is hydrolysed by water
- C-halogen bond breaks heterolytically producing ions
give two reasons why cracking of larger alkane molecules is important in industry
- shorter chain alkanes are more useful products
- produces more fuel
- demand is greater for shorter chain alkanes
- produces alkenes for making plastics/polymers
- smaller alkanes give less pollution
- recycles waste products
- as a source of hydrogen
explain the meaning of saturated
- only contains C-C bonds, no double carbon to carbon bonds
- cant undergo addition reactions
explain the meaning of a hydrocarbon
compounds of hydrogen and carbon molecules only
how would you measure the mass of propane which was burned
measure mass of cylinder before and after burning
( combustion ) suggest one source of error other than heat loss and limitations of equipment
- incomplete combustion
- carbon monoxide or soot forms
give a reason why the value calculated using mean bond enthalpy is less exothermic than the data booklet
- mean bond enthalpy calculation is based on H2O (l)
- data booklet based on H2O (g)
give a reason why the equation in a catalytic converter may not proceed as expected
NO might react to CO
give one reason why biodiesel is now preferred to petrodiesel
- renewable source
- cleaner burning
- better lubricant
explain how oxides of nitrogen and sulfur can be formed from the combustion of fossil fuels
- because sulfur compounds in fuel react with oxygen in air
- because nitrogen in the air reacts with oxygen from air
devise an experiment for the hydrolysis of 1-chlorobutane, 2-bromobutane and 2-iodobutane. state the trends in rate of reaction.
fair test
- use of equal volumes
- warm the tubes in a water bath
silver nitrate + dilute nitric acid + ethanol
find the time taken for precipitate to form
expected trend
- 2-iodobutane>2-bromobutane>2-chlorobutane
- bond enthalpy C-I>C-Br>C-Cl
state the purpose of the condenser
- condenses volatile reactants so they are not lost
- prevents loss of reactants so that they have time to react
what does cracking crude oil do in terms of carbon atoms
- decreases the average number of carbon atoms per molecule
what is the atom economy of polymerisation
100% as only one product
explain why isomers of an alkane has a lower boiling point and are found in the petrol fraction
- isomers in petrol fraction have branched chains
- branched chains have lower surface area / do not pack closely together
- london forces are weaker
what is meant by the term free-radical
particle with unpaired electron
