How much calcium carbonate is in the shell of the snail?

In Year 12 chemistry, we have been doing an experiment in order to find out how much calcium carbonate is in the shell of the snail (don’t worry; no snail was harmed). So first, I had to look around the school grounds to find empty snail shells! This was fun as you can walk around and get some fresh air! It was beautiful weather as well. 

After collecting the shells, I had to grind them up into a fine powder. I then added hydrochloric acid. It immediately fizzed and produced a gas. It was fizzing for about 20 minutes— this was not anticipated— so I stared at the fizzing solution for 10 minutes and realised that fizzing would not stop anytime soon, so I continued on and made sodium hydroxide solution. This part has to be approached with a bit of caution because sodium hydroxide is corrosive and I definitely do not want any chemical burns in my hands.

After making the solution, the fizzing has finally stopped and it was time to filter out all the dirts and sediments using filter paper. This also took some time and involved me looking at slow dripping of snail shell + acid solution (very thrilling, if you ask me!)

Using these two solutions, I now had to carry out a procedure called the titration. This is basically slowly adding an alkali solution to an acid and finding out when two solution became neutral. After finding out the neutralisation point, you can use formulas and other complicated chemistry knowledges— this is a joke, it’s quite simple— to find out how much calcium carbonate was in the shell. The findings from this experiment showed that the snail shell was consisted of 87.5% calcium carbonate. This was lower than our expectation but I’d assume that it was because of impurities in the snail shell (or my research was wrong: they said it was 97%…!).

how much calcium carbonate is in the shell of the snail

This experiment is known as the back titration, because you use titration to not directly find out the calcium carbonate content but work “backwards” to find out the value we want, hence its name “back” titration.

In A level chemistry, experiments are more hands on and experiments are done by ourselves without much help from the teacher. This can be challenging at times, but mostly incredibly fun and teaches you how to work independently. If anybody is considering doing chemistry for their A-level, I would say, go for it! You too can find out how much calcium carbonate is in the shell of the snail and more!

Jaehyeok Hur, Year 12