Deck 1: Making and using alcohols Flashcards
What are the two different chemical processes of making alcohols?
- The hydration of ethene, C2H4. - The fermentation of sugars.
Describe the process of hydrating ethene to form ethanol.
- The reaction is carried out at a high temperature and pressure.
Describe the process of making ethanol from fermentation( also give an equation)
- Carbohydrates are converted into ethanol and carbon dioxide. Sugar or starch is usually used as a carbohydrate source.
- Fermentation is carried out in solution at realtively low temperatures, in the presence of yeast. The reaction is catalysed by an enzyme called zymase.
Explain why the reaction is carried out at low temperatures.
The reaction is slow at temperatures below 25C because at temperatures above 37C, the enzyme starts to denature and lose its efficiency.
Why is the ethanol produced by fermentation never higher than the concentration of about 14%?
The toxicity of the alcohol also limits the concentration of ethanol produced, this is because the enzyme ceases to function above an alcohol concetration of 14%.
Why does the fermentation of ethanol have to be done in the presence of no oxygen.
- Fermentation anaerobic
- With oxygen , ethanal or ethanoic acid produced.
Give some general examples of were alcohol is used?
-Used in perfumes, aftershaves, cleaning fluids and alcoholic beverages.
Describe the use of ethanol in methylated spirits.
Methylated spirits consists of ethanol mixed with small amounts methanol and a coloured dye.
- Methylated spirits is used as a solvent for removing paint in ink stains from clothing, and as fuels in spirit burners.
Why do alcohols have relatively high melting and boiling points?
Because they have hydrogen bonding.
Define volatility
Volatility is the ease that a liquid turns into a gas. Volatility increases as boiling point decreases.
What does the presence of hydrogen bonds in alcohol molecules affect its properties?
The presence of hydrogen bonds in alcohol molecules results in alcohols having a lower volatility than alkanes of similar molecular mass.
Why can alcohols dissolve in water?
Alcohols dissolve in water because hydrogen bonds form between the polar -O-H groups of the alcohol and water molecules.
Which members of the alcohol homologous series are soluble in water?
- The first three members:
- Methanol
- Ethanol
- Propanol
Why is it that when 50cm^3 of ethanol is mixed with 50 cm^3 of water in a 100cm^3 measuring cylinder the total volume is only 98cm^3?
When water and ethanol are mixed together, hydrogen bonds form between water and ethanol molecules. These draw molecules closer together than in pure ethanol or pure water, reducing the volume.
