C6 - Alcohol and Ozone Flashcards
What is an alcohol? What are some uses?
- contain carbon, hydrogen, and oxygen bonded together.
- They often burn well
- ethanol is used as fuel for cars, as a solvent in perfumes and aftershaves , and alcoholic drinks
How is alcohol made through fermentation? Word and symbol equation?
Yeast contains enzymes that can convert glucose to carbon dioxide and ethanol, as long as oxygen is kept out.
glucose → carbon dioxide + ethanol
C6H12O6 → 2CO2 + 2C2H5OH
Explain the conditions chosen for fermentation.
Not below 25 °C - yeast is made up of living organisms. They will become inactive if the temperature is too low
Not above 50 °C - Enzymes are proteins that need to maintain a particular shape, otherwise they will not work. If enzymes become too hot, their shape changes irreversibly. They become denatured and stop working.
No air - oxygen causes the ethanol to oxidise to ethanoic acid
How can ethanol be made through the hydration of ethene? Give a word and symbol equation. What is this method used for?
Ethanol is made by reacting ethene with steam. The two gases are passed over a hot phosphoric acid catalyst, causing a hydration reaction to happen:
ethene + water → ethanol
C2H4 + H2O → C2H5OH
This method is used for ethanol intended for industrial use, rather than ethanol intended for alcoholic drinks.
Give the advantages and disadvantages of the hydration method and fermentation.
Hydration advantages:
- high purity of product ( no by - products)
- high percentage yield ( about 100%)
- high atom economy (100%)
- continuous process
Hydration disadvantages:
- non renewable - ethene needed for process comes from cracking crude oil
- needs high temperatures and pressures - expensive
Fermentation advantages:
- low temperatures and normal temperatures ( cheap )
- renewable - raw material = sugar from plants
Fermentation disadvantages:
- low purity of product
- low percentage yield ( about 15%)
- 51% atom economy
- batch process
What is the general formula of an alcohol? Give the formulas for : methanol, ethanol, propanol, butanol, pentanol
General - CnH2n+1OH Methanol - CH2OH Ethanol - C2H5OH Propanol - C3H7OH Butanol - C4H9OH Pentanol - C5H11O
What is ozone and how does it form? Equation? Why is important?
- Ozone is a form of oxygen with the formula O3.
- Sunlight contains ultraviolet light which causes oxygen, O2, to react to form ozone, O3.
- General equation : 3O2 → 2O3
- Important because the ozone layer absorbs most of the ultraviolet light in sunlight, stopping it from reaching the Earth’s surface.
What are CFCs? What were they used for?
CFC = chlorofluorocarbon.
- They were used as refrigerants in refrigerators and air conditioning systems that carry the heat away.
- They were also widely used as aerosol propellants.
How do CFCs damage the ozone layer?
CFC molecules spread out in the atmosphere after release. Ultraviolet light in the stratosphere breaks carbon-chlorine bonds in CFC molecules. For example: CCl3F → CCl2F + Cl
Highly reactive chlorine atoms called chlorine radicals are released. These react with ozone molecules and break them down to form oxygen, O2. Chlorine atoms are formed in this reaction, and they can go on to react with even more ozone molecules. The reactions reduce the concentration of ozone in the ozone layer, letting more ultraviolet light reach the Earth’s surface.
What can increased levels of ultraviolet cause?
• skin cancer
• an increased risk of sunburn
• an increased risk of eye cataracts
• faster ageing of skin, causing more wrinkles and age spots
Explain in detail, with an equation, how radicals form. Then explain how these damage the ozone layer with further equations. Sum it up with an overall equation.
Ultraviolet light can break a covalent bond in such a way that each atom from the bond gets one of the electrons. This produces highly reactive radicals. This equation shows how a CFC molecule can form a chlorine radical:
UV light
CCl3F �� → •CCl2F + •Cl
These chlorine radicals can go on to damage many ozone molecules.
1. Chlorine radical reacts with ozone •Cl + O3 → •ClO + O2
2. New radical reacts with more ozone •ClO + O3 → + 2O2 + •Cl
This sets up a chain reaction in which a lot of ozone is destroyed. Overall equation : 2O3 → 3O2
What are the properties of CFCs?
• low boiling points, so they are usually gases
• insoluble in water
• chemically inert, so they do not react easily with other substances.
Describe briefly the Montreal Protocol.
Experiments, calculations, and observations made in the 1970s showed that CFCs were destroying ozone and depleting the ozone layer. At a meeting in Montreal in Canada 24 countries signed a treaty that placed strict limits on the production and use of CFCs. Since then, almost all countries have signed it.
What are some replacements for CFCs?
They include alkanes, and compounds called hydrofluorocarbons or HFCs. These do not contain chlorine atoms and they do not damage the ozone layer.
