REGIONAL TECHNICIANS GROUP

Problems and Solutions - Recipes


Ammonia gas and the 'Fountain Experiment'

Getting the 'Fountain Experiment' to work can prove to be very difficult, the dryness of the gas and of the fountain flask being of utmost importance. The standard laboratory preparation of ammonia gas involves heating a mixture of calcium hydroxide and an ammonium salt - water is produced in this reaction as well as ammonia gas.

Using calcium oxide in stead of calcium hydroxide produces half the quantity of water in the reaction, therefore is easier to dry, and more likely to produce a successful 'fountain'.          Good luck!


Blood - artificial

Recipe No.1


Bromine water

Bromine is an extremely dangerous substance to handle - great care must be taken when handling and breaking open the ampoules. To purchase bromine, a poison permit must first be obtained (bromine being a Schedule 7 poison.)

Bromine water may be prepared more safely by adding a few drops of commercial bleach to a strong (0.5M) solution of potassium bromide. The chlorine in the bleach replaces the bromine in solution, and a brown solution of 'Bromine Water' is produced.

This recipe is suitable for preferential solution experiments (i.e. halogens dissolve more readily in organic solvents than in water), but is not as successful with addition and substitution reactions in organic chemistry. For this purpose, it is best to bubble chlorine gas into the potassium bromide solution being careful not to have chlorine in excess (i.e. don't aim for too deep a brown coloured solution!). Chlorine MUST be prepared in a fume cupboard.

Hint 1: See 'Chlorine gas - laboratory preparation' to prepare chlorine without heating.

Hint 2: Turpentine can be used as the organic solvent in preferential solution experiments rather than the more toxic dichloromethane. Ensure that the turpentine is fresh and hasn't started to turn yellow.


Bubble mixture recipes.

Recipe 1 (for general large bubbles):

Recipe 2 (for longer lasting bubbles):

Recipe 3 (for bouncing bubbles):

(this solution will need to be re-heated before use)

All mixtures benefit from the addition of some "toy store" bubble mixture - up to 1 container of bubble mixture in 15 litres of made up solution but quantities may be varied with experimentation.

All recipes courtesy Andrew Suttar, Bubblemania


Chlorine gas - laboratory preparation without heat

Use potassium permanganate in stead of manganese dioxide to prepare chlorine as the reaction does not require heating. This avoids the extra hazard of hot concentrated hydrochloric acid - and the reaction is easier to control if the acid is added via a dropping funnel.

!!ALWAYS prepare chlorine in a FUME CUPBOARD!!


Dialysis tubing - will open easily!

Before cutting lengths of dialysis tubing, rub the end of the tubing between thumb and finger under a gentle stream of running water. When the surfaces of the tube begin to slide over one another, roll out the total length of tubing required and blow into the wetted end. The tubing will open easily and may then be cut into the lengths required.


Euglena culture medium

Stir about ½ teaspoon of yeast powder into 1 litre of boiling water and add 1 frozen pea. When the solution has cooled to room temperature, inoculate with Euglena and loosely cover the container (e.g. with a petri dish lid.) Store the container in a well lit place but not in direct sunlight.

Ensure that all glassware used is scrupulously clean and sub-culture often.

A similar solution may be prepared for Paramecium, but without the frozen pea.


Eyes - freezing for dissection

Sheep eyes obtained for dissection deteriorate rapidly and, if frozen, the lens will go cloudy and no longer be suitable for the dissection exercise.

Eyes will, however, maintain their clarity if placed in 0.9% sodium chloride solution before freezing, making sure that the eyes are immersed lens downward in the solution.

Thanks to Alice Thomas Thornlie Senior High School for this tip.


Food samples - recipes for STAWA Human Biology Laboratory Exercise 19

Sample A. Sample B. Sample C. Sample D.
Starch powder
Gelatin powder
Washed white sand
Glucose powder
Starch powder
Washed white sand
Glucose powder
Starch powder
Gelatin powder
Washed white sand
Glucose powder
Starch powder
Gelatin powder
Washed white sand
Finely grated cheese


Iodine/potassium iodide solution - in less time

The standard recipe for preparing I2/KI solution is 3g iodine crystals + 15g potassium iodide dissolved in 1L water.
To speed up solution of the iodine, dissolve the potassium iodide in as little water as possible (about 20mL) then dissolve the iodine crystals in this solution (iodine dissolves rapidly in concentrated KI solution) - then make up to 1L with distilled water.


Magnets - cleaning off iron filings

Magnets are best protected from iron filings by placing in a small plastic bag or wrapping with cling-film before use. However, when the inevitable happens, it can be a very tedious job trying to pluck the filings from the magnet. 

This job can be made much easier by using adhesive tape to remove the filings.

Thanks to Connie Reed from Hedland S.H.S. for this time saving tip. 


NO2 test solution for "Air Watch" programme - long term storage

Due to the small quantities of solid ingredients used in preparing this solution, it is normal to make up a much larger quantitiy than is required to produce the test papers (which must always be freshly prepared.) Only very small quantities of nitrogen dioxide in the atmosphere will quickly turn the normally colourless solution to pink.

Fran Constable from Ocean Reef S.H.S. has overcome the problem of long term storage by replacing the air inside the volumetric flask, containing the left over solution, with carbon dioxide. The solution has remained useable for over a year.

Thanks Fran for a great time saver.


Nylon - laboratory preparation, an alternative recipe

All stages of this preparation should be performed in a fume cupboard.

Solution A:

Dissolve 5g of 1,6-diaminohexane in 100mL of distilled water.

(Hint: the melting point of 1,6-diaminohexane is around 40oC and is usually solid in the bottle. In a fume cupboard, remove the cap from the bottle, place the bottle in an open watertight plastic bag to protect the label and immerse in a beaker of water held at around 55oC on a hot plate until the 1,6-diaminohexane can be poured - DO NOT heat above this temperature as it will start to decompose. Its flash point is 84oC.)

Solution B:

Dissolve 5mL of adipoyl chloride in 100mL cyclohexane.

(Adipoyl chloride is available from chemical suppliers in 25mL bottles.)

Method:

Pour 20mL of solution A into a 100mL beaker and add 1mL of 6M sodium hydroxide solution.
Carefully pour 20mL of solution B down the side of the beaker to form a layer on top of solution A.
The nylon layer formed can be slowly withdrawn in the normal manner using forceps or a copper hook.
Rinse the nylon produced several times in water before allowing to dry on paper towel.


Paramecium culture medium

Stir about ½ teaspoon of yeast powder into 1 litre of boiling water. When the solution has cooled to room temperature, inoculate with Paramecium and loosely cover the container (e.g. with a petri dish lid.) Store the container in a low light area to discourage the growth of Euglena.

Ensure that all glassware used is scrupulously clean and sub-culture often. Avoid contamination with Euglena as these will quickly take over the culture.

Euglena culture medium can be prepared the same way, but with the addition of a frozen pea.


Philips head screws - removing screws with damaged heads

Damage slots in philips head screws may be lengthened and deepened using an engraver enabling a larger screwdriver to be used.


pH solutions

Standard pH solutions may be easily prepared using the following recipes:

pH2 0.01M hydrochloric acid    
pH3 80mL  0.1M citric acid plus 20mL 0.2M disodium hydrogen phosphate
pH4 62mL  0.1M citric acid plus 38mL 0.2M disodium hydrogen phosphate
pH5 48mL  0.1M citric acid plus 52mL 0.2M disodium hydrogen phosphate
pH6 37mL  0.1M citric acid plus 63mL 0.2M disodium hydrogen phosphate
pH7 18mL  0.1M citric acid plus 82mL 0.2M disodium hydrogen phosphate
pH8   3mL  0.1M citric acid plus 97mL 0.2M disodium hydrogen phosphate
pH10 0.1M sodium hydroxide    

These solutions are sufficiently accurate for use in the cell membrane activity in Biology and also for general pH testing. 

Thanks to Diana Hackett - Kent Street S.H.S. for this information.


Phenoxytol storage solution for preserved animal specimens

An alternative to formalin based or 70% ethanol storage solutions is phenoxytol.

10mL phenoxytol (2-phenoxyethanol)
50mL glycerol
940mL distilled water

It must be noted that this solution is a storage solution only, and fresh specimens must be properly preserved before storage eg. preserve animal specimens in 10% formalin for 3 weeks, wash well to remove the formalin, then transfer to the storage solution.
Already preserved specimens may be transferred to the storage solution after first washing in water. With phenoxytol solutions, specimens do not need to be completely immersed - although for presentation, it is preferred.


Physarium (Slime Mould)  - an alternative culture technique.

Dampen a synthetic kitchen sponge (any colour except yellow) with distilled water and place inside a take-away food container. Inoculate with an oatmeal flake covered in Slime Mould and continue to feed the culture with a fresh oatmeal flake every day, keeping the sponge damp (but not saturated) at all times. Cover the container with a lid or with plastic wrap.

Start a new culture when the old one begins to become contaminated with other moulds. The Slime Mould grows quite happily and synthetic sponges are less expensive than agar and easier to prepare.

Other substrates may also be tried e.g. super-wipe type cloths or paper towels.

Thanks to Joy Unno, Mindarie Senior College, for this information.


Potato as an alternative culture medium for fungus and bacteria.

Peel a large potato and cut into 6mm thick slices.
Place potato slices in boiling water and boil for 1 minute.
Use sterilised tweezers to transfer each slice to a sterile petri dish and allow to cool.
Inoculate the same way as for agar plates.

Potato is particularly good for culturing microbes from soil.


Protein Testing - modified Biuret Reagent

Protein testing using Millon's Reagent and the Sakaguchi Test (which contains 1-naphthol) are potentially hazardous for High School student use. The alternative Biuret Test can also be hazardous as some recipes call for high concentrations of caustic reagents (4M sodium hydroxide or 6M potassium hydroxide). The following is a safer alternative:

Reagent 1 - 'Strong Alkali Solution' - (1M sodium carbonate solution is sufficient)
Reagent 2 - 'Dilute Copper Sulfate Solution' (0.1M  copper-II-sulfate solution)

Method: To a small sample of the material under test, add 1 eye-dropper full of strong alkali solution and 1 drop of dilute copper sulfate solution. The solution will turn violet in the presence of  protein or will remain pale blue in the absence of protein.

Thanks to Carole Peters - PEAC (Primary Science) for this one.


Sakaguchi  recipe for protein testing.

        2 drops of   5% NaOH (sodium hydroxide)
        2 drops of   a-napthol
        2 drops of bleach                                      
        This will give a red precipitate if protein present. 
        A far safer alternative is the recipe above for the modified Biuret Reagent. It is not recommended that the Sakaguchi recipe be used in High Schools.


Saliva - artificial

A solution of 1% diastase (salivary amylase) is a safe substitute for saliva in digestion experiments.
(Make sure that the diastase purchased is free from reducing sugars - click here for suppliers.)

Thanks Eleanor Garrett - Governor Stirling S.H.S. for this info.


The action of saliva on starch - another view.

The standard procedure for this experiment is to react starch solution with saliva and then test for the production of sugar.

As an alternative, add iodine solution to starch solution in two different test tubes then add artificial saliva solution to one of them. Place the tubes in a beaker of warm water (37C).

As the starch is digested by the enzyme, the blue colour gradually disappears, whereas the solution in the tube with no enzyme remains blue.


'Slime' recipe using PVA glue

Inexpensive PVA glue is the most suitable for this recipe.

Prepare a 4% solution of borax (4g sodium tetraborate in 100mL water.)
Mix 25mL of PVA glue with 25mL water and stir well.
Food colouring may be added at this stage if required.
Slowly add 15mL of the 4% borax solution to the diluted PVA, stirring constantly.
Remove the polymer produced and wash well with water.

(Thanks to Dianna Hackett - Kent Street S.H.S. for this recipe.)


Slime - 'Green Slime' using guar gum

Guar gum forms a cross-linked polymer when mixed with sodium tetraborate (borax). The polymer has the consistency of slimy 'goo'. (Guar gum is available from health food shops.)

Solution A:

Add 10mL of glycerine to 200mL of water and mix well..
Add a few drops of green food dye.
Slowly sprinkle in 5g guar gum, stirring continuously until dissolved .

Solution B:

Dissolve 2g borax in 10mL water

Pour solution B into solution A and mix well - the polymer forms rapidly.

(Thanks to Elaine Young - Girrawheen S.H.S. for this one.)


Starch solution - an easy preparation method

Mix the required amount of starch powder into a smooth paste with a small amount of cold water. Pour this paste into the required amount of boiling water and stir rapidly. The starch suspension will form immediately, usually without any lumps.


Universal indicator paper - make your own

Simply dip strips of filter paper into universal indicator solution and allow to dry.
Because of the natural acidity of the paper, the colour turns yellow - this may be buffered slightly by first dipping the strips of filter paper in 0.1% sodium bicarbonate solution and allowing to dry before dipping in universal indicator solution. The resulting strips are coloured green.

(Thanks to Rosemary Gillen - Geraldton Secondary College for this idea.)


Urine - artificial

With the use of body fluids now very questionable in secondary schools, most laboratory investigations can be carried out using artificial solutions. The following recipes provide 500mL each of artificial urine:

To 500mL distilled water add:

  SAMPLE  

GLUCOSE

SALT (NaCl)

 UREA 

ALBUMEN

 pH

A

0.1g

0.6g

2.0g

5.0g

 approx. 6

B

-

0.6g

2.0g

-

 approx. 6

C

1.4g

0.6g

2.0g

-

add 2mL
2M NaOH

D

0.5g

5.0g

2.0g

-

 approx. 6

E

3.0g

0.6g

2.0g

-

 approx. 6

F (control)

-

-

-

-

7

Food colours or stains can be added to 'suit'.

Eggwhite can be used for albumen, but powdered albumen works best. This is available from chemical suppliers, or small amounts can be obtained from cake decorating shops or sometimes from bakeries (product is usually known as "Actiwhite").

Conclusions can be drawn from tests on the above samples regarding the condition of the 'patient'.

Many thanks to Gary Gardener (Governor Stirling Senior High School) for the above contribution.


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