Investigating osmosis in chickens’ eggs
In this procedure, you can observe osmosis in an animal system by using chickens’ eggs from which the shells have been removed by dissolving in acid. The eggs are weighed and placed in solutions of different strength for 24-48 hours before being weighed again.
You can run this as a demonstration, or a class practical where pairs of pupil have an egg and each pair place their eggs in different solutions (amalgamating results to provide whole-class data). If you can manage the number of eggs, each group could have three eggs.
Apparatus and Chemicals
For each group of students:
Beaker, 200 cm3
150 cm3 of each salt solution to be used.
For the class – set up by technician/ teacher:
De-shelled eggs (Note 1)
Sodium chloride solutions in a range of concentrations, for example, 0%, 10%, 20%. (150 cm3 of each concentration for each working group)
Health & Safety and Technical notes
Hydrochloric acid (HCl) is described as IRRITANT at concentrations above 2.0 M, causes burns and is irritating to the respiratory system. Technicians will need to take precautions when preparing the eggs, but the rinsed eggs should be low hazard for students to handle.
Sodium chloride is described as low hazard. See CLEAPSS Hazcard.
Wear eye protection as some of the sodium chloride solutions are strong.
Rinse hands if splashed by solutions.
1 To de-shell chicken’s eggs, leave overnight in a large beaker of acid (1.5 M - 2 M of hydrochloric acid is ideal). This will dissolve the shells. Weigh down the eggs with a second beaker containing water, so they are pushed down into the acid and do not float above the surface. This ensures all the shell is removed and there is not a patch left. Trying to pick off a patch will break the egg! Rinse the eggs before use. A de-shelled egg is strong enough to handle with care. If consecutive lessons are several days apart, store the eggs in solutions in the refrigerator.
These eggs are sold as foodstuffs and are unlikely to be fertile. There may be ethical issues associated with farming processes, but not specifically with this use of the eggs. Students who are vegetarians or vegans may object to handling animal material.
SAFETY: Make sure the acid is rinsed off the eggs before use.
a De-shell the eggs in acid overnight. Rinse before students handle them.
b Ensure the egg is dry by gently patting it with a paper towel.
c Place the egg on a balance and record the mass in a suitable table.
d Put the egg in a 200 cm3 beaker.
e Pour in enough sodium chloride solution to cover the egg. Record the concentration of sodium chloride used.
f Leave the egg until next lesson – at least 24 hours.
g Pour the sodium chloride solution off the egg.
h Dry the egg carefully using a paper towel.
i Place the egg on the balance and record the mass in the table.
j Calculate change in mass and percentage change in mass.
k Compare the results for the different concentrations of sodium chloride.
The egg is not a single animal cell. However the egg’s membrane is selectively permeable, so it is a good model to show osmotic effects in animal tissue.
Run the practical by following the procedure, or as investigations with the following variations.
- Use a full range of salt solutions 0%, 5%, 10%, 15%, 20% etc.
- Time: Put the eggs in either distilled water or 20% salt solution. Remove and weigh at timed intervals, for example, every 10 minutes.
- Temperature: Put eggs in a fixed solution at different temperatures, such as 0°C, 5°C, 10°C, 15°C, 20°C, 25°C, and weigh after a fixed time, for example, 30 minutes.
Health and safety checked, September 2008
Download the student sheet Investigating osmosis in chickens' eggs (54 KB) with questions and answers.