Scientific Experiment: Decarbonating Soft Drink

To calculate the volume of carbon dioxide gas when decarbonising soft drinks (soda water) at a room temperature (around 25 degrees) and air pressure at 100kPA.

Activity 2 – Decarbonating Soft Drink

Aim

To calculate the volume of carbon dioxide gas when decarbonising soft drinks (soda water) at a room temperature (around 25 degrees) and air pressure at 100kPA.

Background

        i.            Research, record, cite sources for data on CO2 (including solubility in water and any other properties you consider relevant.

Solubility of CO2 gas (g/Kg) in water at 101.325kPA: 0°C – 3.35g/kg, 20°C – 1.69g/Kg, 25°C – 1.45g/kg, 30°C – 1.26g/Kg, 35°C – 1.10g/Kg, 40°C – 0.973g/Kg, 60°C – 0.576g/Kg

      ii.            Use Le Chatelier’s Principle to describe how changes in pressure and temperature can assist in removing CO2 from soda water. Include relevant equations.

Le Chatelier’s principle states that if a system at equilibrium is disturbed, then the system will adjust itself in order to minimise the disturbance. Before a bottle of soft drink is opened, the system is at equilibrium, with a significant concentration of CO2 dissolved in the solution at high pressures:

CO2 (aq) + H2O(l) -> <- H2CO3(aq) -> <- H+(aq) + HCO3_(aq)­

Changes in the equilibrium position can remove CO2 from soda water:

      When a soft drink bottle/can is opened, the high pressure CO2 escapes. When the pressure of CO2 is decreased, the balance of system is upset and in accordance with Le Chatelier’s principle, H2CO3(aq) is decomposed into CO2 to counteract this loss of pressure in CO2. Hence the equilibrium is shifted to the left and CO2 is removed from the soda water.

      Change in total pressure allows pressure to ‘escape’ when opening a bottle. In this case, the equilibrium moves to the direction that loses pressure which is to the left as high pressured CO2 escapes.

      If a soft drink is opened in warmer temperatures, bubbles are produced more rapidly. This is because the equilibrium concentration of CO2 at the higher temperature is lower (as seen in the background information) and so more CO2 escapes as solubility of CO2 in water decreases as temperature increases.

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