Decarbonation of Soda Water

My Year 12 Chemistry class were working on this *exciting* prac this afternoon, as part of developing their understanding of the equilibrium that occurs in the dissolution of carbon dioxide in water.

In the past, I have done this experiment as you might expect – take a small can of soft drink, crack the lid and let it sit for a few days alongside a control containing the same mass of water. You measure the mass of the cans before and after and calculate the mass lost due to CO2 loss. The control can helps to account for any evaporation, which tends to be most of the loss anyway. Not very exciting and not a lot of CO2 lost.

This time around I tried the salting out method, where you add 1-2 g of salt for every 50 mL of soda water. This causes the CO2 to effervesce immediately, leading to a totally flat bottle in about 10 minutes instead of days. Here are some sample photos:


20140522-165027-60627749.jpgAs you can see, some groups added some universal indicator to see if there was any colour change. The fizz at the top was distinctly yellow-orange, but interestingly the rest of the bottle stayed the same colour. A far more effective method – definitely a keeper!

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