Time for another seasonal post. It’s nearly Easter so you may wish to have a go at some egg-based science experiments this week.
For an interesting spin on a lesson on chemical reactions you could try making a ‘naked egg’, that is an egg without its shell.
The shells of eggs are mostly calcium carbonate so will react with acids to form carbon dioxide and a calcium salt. This reaction will result in the shell ‘disappearing’ leaving the egg with just its membranes to cover its modesty.
You could carry out this reaction with hydrochloric acid ( 1M- 3M should work) before the lesson. This video shows how:
You could then present the egg in class and ask the students to come up with ideas as to how you removed the shell.
If they have already done some work on neutralisation or acid rain, telling them that the shell is calcium carbonate may give some clues.
You could then demonstrate the reaction again for them whilst asking them to explain their observations e.g. the froth is the carbon dioxide being released, is the shell really disappearing? They can also write chemical equations of the reaction.
The egg will not take very long to be stripped of its shell but be sure to remove it before the egg white becomes denatured and rubbery, as this is not nearly as much fun as a squidgy egg (but could be good for discussions on protein denaturation for a KS4 class – see teaching idea below).
For KS2 classes you could ask them to try this experiment out at home over the holidays using vinegar. They could use sources on the internet to find out why the experiment works.
The naked eggs can be used for experiments looking at osmosis. Students measure the size of the egg before and after leaving overnight in a salt solution or distilled water. The egg in salty water will shrink as water is lost from it via osmosis, the one in distilled water will increase in size.
For another eggy lesson, you could show the students how to ‘cook’ an egg without using any heat. Adding an egg to acid as shown in the video in the weblink below will ‘cook’ the egg white. This is because of the albumin protein in the egg white denaturing because of the low pH. This so-called ‘chemical cooking’ is used in dishes such as cerviche where fish is added to citrus juice. The egg yolk, though, remains unchanged – you can ask students to think about why this is. My hypothesis is that the yolk is mainly fat with little protein so won’t be affected by the acid.
Have a very happy Easter break!
Information on the science of eggs.
Instructions for making a naked egg using vinegar – an experiment suitable for KS2 students to do at home
Cooking an egg in acid video