Specifications

Core Practicals

Alcohols and Carboxylic Acids

Homologous Series: Alcohols

Alcohols are one example of a homologous series. They:

  • have the general formula of CH₂ₙ₊₁OH

    • this means that for every 1 carbon atom in an alcohols, there are two times the amount of hydrogens... plus one more, and an OH group

  • differ by CH₂ in molecular formulae from neighbouring compounds

    • increasing the carbon chain length by 1 carbon atom, also increases the number of hydrogens by 2

  • show a gradual variation in physical properties

    • boiling points increase with increased carbon chain length

    • viscosity increases with increased carbon chain length

  • have similar chemical properties

  

Alcohols have the functional group of -OH (hydroxyl), and it gives rise to the ending of alcohol. It is responsible for the general reactions that all alcohols can do.

80 alcohols-01.png

Production of Ethanol

glucose → ethanol + carbon dioxide

  

Most ethanol is made from plants, making it a renewable resource. The process is called fermentation, and requires:

  • water

  • yeast enzymes

  • an absence of oxygen (an anaerobic process)

  • temperatures between 25 - 35 °C

  

The yeast dies when the ethanol concentration reaches about 15%.

  

Fermentation is a slow reaction and takes several days or weeks to finish. If any air is present, the oxygen oxidises the ethanol to make ethanoic acid, making the drink taste of vinegar. 

  

Fermentation will produce a dilute solution of ethanol, and needs to be purified to remove water and other liquids (removed by fractional distillation), insoluble substances (removed by filtration), to produce pure ethanol.

Core Practical 8: Combustion of Alcohols

Apparatus set up to measure the increase in temperature when the different fuels given are burned.

  

This must lead to a comparison of the results for the four alcohols.

Method 

  1. secure a conical flask over a spirit burner so that the lid of the burner can be removed and replaced safely

  2. measure and record the mass of a spirit burner with its lid

  3. use a measuring cylinder to add 100 ml of cold water to the flask, and then record its temperature

  4. place the spirit burner underneath the flask, remove the lid and light the wick

  5. stir the water carefully with the thermometer until the temperature has increased by 20°C, then replace the lid to put the flame out

  6. measure and record the new mass of the spirit burner (with lid), and the maximum temperature that the water reached

  7. repeat steps 2-6 with different alcohols, starting with new water every time

combustion-01.png

Homologous Series: Carboxylic Acids

Carboxylic acids are one example of a homologous series. They:

  • have the general formula of CH₂ₙ₊₁COOH

    • this means that for every 1 carbon atom in a carboxylic acid, there are two times the amount of hydrogens... plus one more, and an COOH group

  • differ by CH₂ in molecular formulae from neighbouring compounds

    • increasing the carbon chain length by 1 carbon atom, also increases the number of hydrogens by 2

  • show a gradual variation in physical properties

    • boiling points increase with increased carbon chain length

    • viscosity increases with increased carbon chain length

  • have similar chemical properties

  

Carboxylic acids have the functional group of -COOH (carboxyl), and it gives rise to the ending of carboxylic acid. It is responsible for the general reactions that all carboxylic acids can do.

80 carb acids-01.png

Reactions of Alcohols and Carboxylic Acids

Alcohols

  • colourless liquids that dissolve in water to form neutral solutions

  • can be dehydrated to form alkenes (produces a water molecule)

  • will react with the alkali metals to produce hydrogen and a metal hydroxide (like sodium would with water)

  • burn in air to produce carbon dioxide and water (complete combustion)

  • can be oxidised to make a carboxylic acid in the presence of an oxidising agent (shown as [O])

Carboxylic acids

  • dissolve in water to form acidic solutions (pH values less than 7)

  • react with metals to form a salt and hydrogen

  • react with bases to form a salt and water

  • react with carbonates to form a salt, water and carbon dioxide

 
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