Organic Chemistry Flashcards
How do the physical properties of alkanes and alkenes change on going down the series (increase in carbon atoms)?
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Their melting and boiling points increase.
- Reason: Alkanes are covalent compounds and have simple molecular structures. Alkanes with more C atoms have a bigger relative molecular mass (Mr). Larger amount of energy is needed to overcome the stronger intermolecular forces of attraction in alkanes with more C atoms.
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They become more viscous (flow less easily).
- Reason: As the molecular masses of alkanes increase, more energy is needed to overcome stronger intermolecular forces in these bigger alkanes.
- They become denser.
- They become less flammable (the fractions burn less easily & burn with a more smoky flame).
State the conditions for Hydrogenation to convert alkenes to alkanes
Conditions: 150 °C, nickel catalyst
State conditions for Bromination to alkenes
Condition: Room temperature (25 °C)
State the conditions of Hydration of alkenes to alcohols
Condition: 300°C, 60 atm, phosphoric(V) acid (H3PO4) as catalyst
State how polymerisation of ethene works
At high temperature and pressure and in the presence of catalyst, the carbon-carbon double (C=C) bonds of the ethene molecules break to form carbon-crbon single bonds (C-C). Many ethene molecules join to form long-chain molecule called poly(ethene).
What is cracking?
Cracking is a process where the larger hydrocarbons molecules, usually alkanes are broken down into smaller hydrocarbon molecules by heat and in the presence of catalyst.
Conditions for catalytic cracking
- high temperature, 600°C;
- pressure of about 1 atm
- presence of finely divided aluminium oxide catalyst, Al2O3 or silicon dioxide / silicon(IV) oxide, SiO2 **
Why is cracking important?
- Cracking is used to produce smaller chain hydrocarbons such as petrol which are in great demand as fuels for cars. (e.g. naphtha cracks to petrol)
- Cracking is used to produce short-chain alkenes such as ethene is produced. Ethene is very useful starting material for making ethanol and plastics.
- Hydrogen produced can be used as a fuel. Hydrogen can be used in the production of ammonia.
What happens to the chemical structure of the oil as the margarine is formed?
In vegetable oil, carbon-carbon double bond (C=C) breaks to carbon – carbon single bond. Hydrogen atoms are added to the carbon atoms to form a solid product, margarine.
State the similarities and differences of Alkanes and Alkenes
- Both hydrocarbons and contain a number of carbon atoms
- Both are flammable. On complete combustion, they form carbon dioxide and water
- Both can react aqueous bromine
- Alkane contains carbon-carbon single covalent bonds while alkene contains carbon-carbon double covalent bonds
- Alkanes are generally unreactive while alkenes are very reactive
State the conditions for the fermentation of Glucose
Conditions: presence of yeast, 37°C, absence of oxygen
Why should there a temperature of 37°C, presence of yeast and absence of oxygen for fermentation of glucose?
- Yeast contains biological enzyme that converts glucose to ethanol and carbon dioxide.
- To prevent the oxidation of ethanol to ethanoic acid.
- This is the optimal temperature (37°C) for yeast to function.
- At a higher temperature yeast will be killed and no fermentation of glucose will take place. At a lower temperature, the rate of the reaction will be too slow.
State the conditions for oxidation of alcohols
acidified aqeous potassium manganate(VII)/potassium dichromate (sulfuric acid), warm the mixture
Conditions for esterification
Conditions: concentrated sulfuric acid catalyst, warming
What are isomers?
Isomers are compounds that have the same molecular formula but different structural formula.
