Organic Flashcards
Properties going down the fractionating column
- Chain length increases
- Volatility decreases
- Volatility refers to the tendency of a substance to vaporise. As the size of the hydrocarbon increases liquids the attraction between the molecules increases leading to a lower chance of them vaporising
- Boiling point becomes higher
- As the molecules get larger, the intermolecular attraction becomes greater. More heat is needed to separate the molecules.
- Viscosity increases
- Refers to the ease of flow of a liquid. As the number of carbon atoms increases, the attraction between the hydrocarbon molecules also increases which results in the liquid becoming more viscous with the increasing length of the hydrocarbon chain. High viscosity liquids are thick and flow less easily
Process of fractional distillation
- The crude oil is heated andvapourises
- The vapours of hydrocarbons enter the column which has atemperature gradient
- The vapours of hydrocarbons with high boiling pointscondenseat the bottom of the column
- The vapours of hydrocarbons with lower boiling points rise up the column and condense at the top
What is the bonding and properties of alkanes
Bonding in alkanes is single covalent making alkanes saturated hydrocarbons
Properties of alkanes
- Generally unreactive (except in terms of combustion and substitution by chlorine)
- Colourless
- First 4 are gases at room temperature, 5-17 are liquids at room temp and above are gases
- Boiling point increases as length increases
Bonding in alkanes
Bonding in alkenes includes a double carbon–carbon covalent bond making alkenes unsaturated hydrocarbons
Process of cracking
- Crackinginvolves heating the hydrocarbon molecules to around 600 – 700°C tovaporisethem. The vapours then pass over a hot powderedcatalystof alumina or silica.
- This process breaks covalent bonds in the molecules as they come into contact with the surface of the catalyst, causingthermal decompositionreactions.
- The molecules are broken up in a random way which produces a mixture of smaller alkanes and alkenes
- Hydrogen and a higher proportion of alkenes are formed at higher temperatures and higher pressure
All alkene addition reaction
Bromine
A dibromoalkane is formed. The reaction is characterized by the decolorisation of the bromine solution
Hydrogen
- Conditions: Temperature 150 degrees, nickel catalyst
When alkenes undergo addition reactions with hydrogen, analkaneis formed
Steam
- Conditions: acid catalyst
- When alkenes undergo addition reactions with steam, analcoholis formed.
- Since water is being added to the molecule it is also called ahydrationreaction
Uses of ethanol
- As a solvent
- As a fuel
Formation of carboxylic acid from alcohol
- Oxidation of ethanol with acidified aqueous potassium manganate(VII)
This involves heating ethanol withacidified potassium manganate(VII)in the presence of an acid. The heating is performed underrefluxwhich involves heating the reaction mixture in a vessel with a condenser attached to the top. The condenser prevents the volatile alcohol from escaping the reaction vessel as alcohols have low boiling points
CH3CH2OH (aq) + 2[O] →CH3COOH (aq) + H2O (l)
- The solution will change from purple to colourless
- Oxidation of ethanol by bacterial oxidation during vinegar production
Themicrobial oxidation(fermentation) of ethanol will produce a weak solution of vinegar (ethanoic acid). This occurs when a bottle of wine is opened as bacteria in the air (acetobacter) will use atmospheric oxygen from air to oxidise the ethanol in the wine
C2H5OH (aq) + O2(g) → CH3COOH (aq)+ H2O (l)
Environmental challenges caused by plastics
Disposal in landfill sites
Waste polymers are disposed of in landfill sites but this takes up valuable land, as polymers are non-biodegradable so micro-organisms such as decomposers cannot break them down. This causes sites to quickly fill up. Additionally, there is visual pollution.
Accumulation in oceans
Plastic waste accumulates in oceans causing marine life to become tangled in it and suffocate and also blocks their digestive system causing them to feel full and starve.
Incineration
Toxic gases are formed from their burning contributing to global warming and causing respiratory distress (especially of poly(vinylchloride) which releases toxic hydrogen chloride gas when burned + carbon dioxide + carbon monoxide if incomplete combustion)
Problem with recycling polymers
The conditions needed to break them down, which are usually high temperatures and pressures, can degrade the monomers making them unusable for re-polymerisation
Why are titrations done
Titrations are carried out to calculate the concentration of an acid or alkali by determining how much acid is needed to neutralise an alkali (or vice versa). They can also be done to produce a soluble salt.
- Known concentration goes in conical flask, unknown goes in burette
- For indicators can either use methyl orange (when base is known) or phenolphthalein (when acid is known) because they have a sharp colour change when turning from acid to alkali
Method of titration with unknown concentration of acid and sodium hydroxide 0.1mol/dm^3 concentration
- Use the pipette filler to place exactly 25 cm^3sodium hydroxide solution into the volumetric pipette and add it into the conical flask
- Clamp the burette on the stand and use the funnel to fill the burette with sulfuric acid
- Place an empty beaker underneath the tap and release a small amount of acid to remove any air bubbles
- Record the initial volume on the burette to the nearest 0.05cm^3
- Place the conical flask under the tap of the burette on top of a white tile (to make colour change more visible)
- Add three drops of methyl orange indicator into the conical flask and swirl to mix
- Run the acid from the burette into the alkali while swirling the solution. As the endpoint approaches, reduce the increments and quickly stop titration when it is reached. (colour changes to red if using methyl orange)
- Record the final volume of the burette in a table
- Calculate the rough titre using Final volume - initial volume = Titre volume
- Repeat the experiment until two titres are found that are within 0.1cm^3 of each other excluding the rough titration
- Calculate the mean titre volume
Chromatography method
Equipment: Chromatography paper, pencil, ruler, suitable solvent, suitable sized beaker, soluble coloured substances
- Draw a straight pencil line across, 1cm from the base of the chromatography paper and place evenly spaced spots of the samples along the line
- Add a small volume of solvent into the beaker, roughly less than 1cm
- Place the chromatography paper into the beaker so that it’s stood upright, ensuring the pencil line is above the level of solvent (so that samples don’t wash into the solvent container)
- Wait for the solvent to travel up the paper through capillary action, carrying the different substances in the pigments with it
- Remove the paper and mark the solvent front (line where the solvent went up to) and allow the chromatogram to dry before taking Rf values
The separation occurs because different substances have different solubilities so they will travel at different rates, causing the substances to spread apart.
Test for Al3+
aqueous sodium hydroxide
white ppt soluble in excess
aqueous ammonia
insoluble in excess white ppt
Test for sulfur dioxide
turns acidified potassium permanganate from purple to colourless
How to test for halogens
chloride, Cl –, bromide, Br –, and iodide, I –, by
acidifying with dilute nitric acid then adding aqueous silver nitrate
