Shipwrecks and Salvage prac

[glenpaul]

Heinemann Chem teacher's resource prac book. Prevention of corrosion prac 9.6
How do you make the Agar solution and how much of the indicator sol do you use?
Glenpaul

[sunray18]

This is what we do here: and I pour the agar just before class, so it is just set.

Chem Yr 12 Corrosion,
Ferroxyl Plates

Ferroxyl Indicator:
10g Sodium Chloride
1g Potassium Ferrocyanide
1g Phenolphthalein
In 500 mL distilled water.

Add to 250 mL of Agar solution…
ie 2.5 gm Agar to 250 ml.

Nails used:
A-Bent Nail
B-Galvanised/scraped nail
C-Galvanised nail
D- Nail with Mg/Cu strip
E-Nail with Zinc strip

[AnnNos]

This is how I did it.

Procedure
1) Place 200 ml of de-ionised water in a 500 mL beaker. Heat until the water just begins to boil. Remove the heat and stir in 8 g of powdered agar. Heat gently while stirring until the agar is evenly dispersed throughout the water.
2) Add about I ml of 0.1 M potassium hexacyanoferrate (Ill.) (potassium ferricyanide) and I ml of 0.1% phenolphthalein indicator to the agar mixture and stir thoroughly.
3) Allow the agar mixture to cool until it is lukewarm but still liquid.
4) While the agar is cooling, clean the four nails with emery paper and place one of them in a Petri dish.
5) Use a pair of pliers to bend a second nail into a right angle, and then place it flat in the Petri dish (not touching the other nail).
6) Wrap a piece of bare copper wire or strip around the third nail in a tight helix so that the wire and nail are in good electrical contact. Place the nail and wire flat in the second Petri dish.
7) Take a piece of zinc strip and clean its surface thoroughly with emery paper. Wrap the strip around the fourth nail in a tight helix so that they are in good electrical contact. Lay the nail and strip flat in the second Petri dish (not touching the other nail).
When the agar mixture is cool, pour it carefully over the nails in the Petri dishes until they are covered to a depth of about 0.5 cm. Allow the agar to cool to room temperature and to solidify. Carefully sketch the arrangement of nails in each dish. Place a labelled cover over each Petri dish.
9) Leave the Petri dishes overnight and observe the nails the next day. The areas of blue colouration indicate the area where iron has had its electrons taken from it, while the areas of pink colouration indicate the area where oxygen has taken the electrons..

Worked perfectly.

[Labbie]

We have used 7.5g agar, 500ml distilled water. 10ml 0.1M Phenolphthalein. 75ml 0.1M Potassuyn Ferricyanide, 5ml Soldium Chloride Saturated.

Boil Water & Agar remove from heat, when cool to about 35c add Phenolphthalein, Potassium Ferricyanide, then Sodium Chloride, a few drops of KOH turns the gel pink, HCL will br it back to clear. This is taken from Chemical Redox reactions page 90, its a old book. makes aabout 15-20 plates.
We also use the above nails in the same way.

[nickykinz]

This is how I make my agar. The students do the setting up so I just make the agar and leave it in the water bath set at 50 degrees so they can pour it when ready. The recipe is per 100ml so depends how many groups you are doing how much you need, just multiply up all the quantities.
1g agar powder and 0.5g NaCl (for 100ml). Mix agar powder with a little cold water to make a paste. Make up to 100ml (or equivalent) and then bring to the boil. Then add Potassium Ferricyanide and phenolphthalein. 5 drops of 0.1M Potassium Ferricyanide and 3 drops phenolphthalein. I usually do 150ml per group for 2 petri dishes. Put in bottles and into waterbath set at 50 degrees.
We do the same experiment from the same book and I have never managed to find out how much of the indicator to use which is why I started doing it like this. We have done it for the last 4 years though and it always works.