Secret in the sachet

The Guernsey Flowers Information Bureau needs your help to investigate a homemade flower preservation recipe.

This session should take 70 minutes, though students then need to compare the flowers every week, noting any differences.

Equipment

• Eye protection is essential for preparing the diluted bleach solution
• Measuring cylinders
• Measuring jug
• Beakers
• Glass droppers
• Glass stirring rods
• Teaspoons
• Tablespoons
• Sugar
• Bleach
• Water
• Flowers - carnations (standard and sprays)/roses/ freesias

Health, safety and technical notes

• Read our standard health and safety guidance here.
• This is an open-ended problem-solving activity, so the guidance given here is necessarily incomplete.
• It is advisable to pre-dilute the bleach solution.
• Household bleach solutions (containing sodium chlorate(I) / sodium hypochlorite) sold for the domestic market is most likely to be corrosive (though it may be more dilute and irritant). Even quite dilute bleach is an irritant if more than 0.15 M NaOCl.
• Chlorine gas is released from the bleach, so work should be carried out in a well-ventilated classroom. Pupils with asthma should avoid close proximity to the undiluted bleach. 
• Diluted bleach solutions are of low hazard, but for anything more than very small quantities of bleach, ‘neutralise’ with iron II salts or sodium thiosulphate and then wash to waste.

Possible approaches

Could be used as a ‘fair test’ exercise. Apparently the effect of the preservative solution is most marked on flowers such as carnations (standard and sprays), which have been kept for as long as 3 weeks, and roses. (Freesias have also lasted longer in the preservative solution.)

Don’t use chrysanthemums, as they keep reasonably well anyway.

Always keep flowers in a cool place.

Reason that preservative solution works:

1. Sugar is a food.
2. Bleach kills bacteria.

The flower stems have water channels. Bacteria clog up these channels - the bleach kills the bacteria.

Possible extension

1. What sugar/bleach/water ratio is best?
2. What is the effect of different bleach concentrations?

(If this is investigated, then clearly it will be necessary to make up different pre-diluted bleach solutions, including chlorine and non-chlorine bleaches.)