278.jpg

Soda Can Corrosion

Packaging is important to any food to retain quality.

Packaging is important to any food because it needs to be ableto retain the food’s quality, and the shelf life of the product isdependent on it. Soda pop is very acidic and, having at least twotypes of acids, it needs the polymeric coating that it has or theacids would eat through the can and the results would bedisastrous. I believe that the soda does not react to the aluminumbecause there is a plastic lining protecting the inside of thecan.

Experiment Materials

  • 1 can of soda
  • 2 containers with lids
  • 1 pair of shears
  • A file

Experiment

  1. Distribute the soda from the can in the containers equally.
  2. Cut soda can with shears into 6 equal sized square pieces.
  3. Score deep lines on the inside surface of half of the pieces.
  4. Equally submerge the pieces in the containers and close the lids.
  5. Record observations for each and take pictures.

How Does It Work?

Soda is made up of carbonated water, sugar, and acid. Coke in particular has 0.06% acid and has a pH between 2.4 and 2.8. The acid is used in the coke to add a slightly bitter taste to your mouth when you drink it. Coke mostly contains phosphoric acid and citric acid. In addition to the acid, carbonated water, caffeine, colors, preservatives, and sweeteners are added to the product for a more appealing taste. Packaging is important to any food because it needs to be able to retain the food’s quality, and the shelf life of the product is dependent on it. Coke is very acidic and, having at least two types of acids, it needs the polymeric coating that it has or the acids would eat through the can and the results of that would be disastrous. Preservatives, of course, are added to keep the product fresh because that is what the consumption is based on.

The decision to buy a product depends on how the customer views the product after being battered and bruised from shipping and the taste of the product due to additives. The cascade effect is a chain reaction. If there is a leakage that comes in contact with all of the cans then they will all rust over time due to an “outside to in” corrosion. If all the cans are exposed to a leakage then corrosion can occur and they all become rusted. There is a type of coating that can prevent this ‘outside to in’ corrosion therefore preventing the effect. Usually epoxy and acrylic are used in this coating and are usually water borne. Antioxidants also slow the cascade effect down significantly.

Additional Info

NOTE FROM STEVE SPANGLER SCIENCE: This project was submitted by a wonderful young man but his name does not appear any place on his experiment. He even interviewed one of our scientists for the project, but we do not have his name attached to his write-up. If you are the author, please contact us immediately so we can give credit where credit is due.

Observations

  • Day 1 The pieces with scratches and the pieces with none look the same.
  • Day 2 The scratched pieces look a little brown and the unscratched pieces remain the same.
  • Day 3 There are a few spots on the scratched pieces but the pieces with no scratches look the same.
  • Day 4 More spots are on the scratched pieces and the unscratched pieces remain the same.
  • Day 5 There are even more spots on the pieces with scratches but the other pieces are the same.
  • Day 6 There are still spots on the scratched pieces and none on the unscratched pieces.
  • Day 7 The spots remain stationary and the pieces with no scratches remain the same.

The problem in this experiment was to see what caused acids in soda to not react with the aluminum can in which it was stored. I hypothesized that there was a lining protecting the soda can from the acid. My hypothesis was correct. To perform this experiment I decided to scrape the lining off to see what would happen for a period of seven days to the scratched can in soda. I saw that the scratched pieces developed spots from rust, while the pieces that had no scratches remained the same. The independent variable was the condition of the pieces of can (whether they were scratched or not). The dependent variable was the amount of rust on the pieces. The controls were the coke and the equipment that I used. I learned a lot during this experiment.

From doing research, I found out about canning and the composition of soda which helped me understand my results better. If I were to change something in the experiment I would observe the pieces with scratches for a longer time to see if there were long term effects of the acid and the can. To expand this experiment we could put scratched pieces of coke cans in different solutions and record the reaction for each using the same set time frame of seven days. Another possibility would be to use different metals like copper and iron and see their reaction to soda and to record how long they took to rust. From doing my experiment I can conclude that soda is very acidic and has a devastating effect on anything unprotected. I thought that this was an interesting project to perform and I learned a lot while doing it.