The work of Dr. Mahmoud Marsafy

page updated Dec 23rd 2006

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REMEMBER: you must do your own experiment risk assessment, ideas are illustrated but health and safety details are NOT included

1. A simple mg balance and determination of water of crystallisation

• Photos 3 &4 concern the gravimetric determination of the Formula of CuSO₄ Hydrate. Photo 3, demonstrates the weighing of 100mg of the hydrate salt.  A very sensitive, two pan balance is used ,(please kindly  note the emphasis on the potentiality of safe entirely un-hazardous home experimentation).

• Photo 4 outlines the steps of the dehydration procedure, to replace the conventional technique. A small sheet of Al foil is used to weigh the sample, which is then very carefully  folded to enclose the sample quantitatively. This folded Al sheet replaces the conventional experimental containers for heating the hydrate (i.e crucibles, tubes, flasks, or beakers ) as well as the desiccator, for storing the cooled sample.

• The heating (in the photo) was carried out on a metallic surface on a domestic gas cooker, for only a few minute. The folded Al sheet cools almost instantaneously after removal from the hot plate. Many other methods of heating were found to be just as adequate( Spirit lamp, Bunsen Burner, or Hot plate).

• Weighing a precisely 100 mg sample trains the student for extra skills in weighing and makes the further calculation very easy and readily comprehendible. 

• Please kindly note in step 5 the extent of deviation indicating a loss of 36 mgs (the water of crystallisation in 100mg of the  original sample.  

HISTORICAL NOTE

2. Sodium thiosulphate titration of iodine after the Cu²⁺/I^- reaction

• Photo 1 (above)  presents the conventional technique as adopted in the Futures language school in Cairo, where I am responsible for instructing the AS Students for this year's Exam. Only using a 10 ml Pipette instead of the conventional 25 ml., and a smaller conical flask.

• Photo 2 (below), is a modification using a 10 ml  Graduated Plastic Syringe for pipetting and titrant addition.  The various stages of the progress of the titration has been combined in this composite experimental Chart.

• This technique yields identical precise results as the conventional techniques.  A two ml syringe, and even a 1 ml syringe have been found to be reliable, dependable , and just as accurate. In this case a quite small vial replaces also the small conical flask. 

The above diagram presents very safe controlled micro-scale heating with various appliances.  The reaction tube is stoppered with a plug of tissue paper. This is a very useful safety feature incorporated in the design of the experiment. The reaction presented was the mild reduction of Cu²⁺ cation with glucose in alkaline medium resulting in the brick red Cu₂O product.  This of course is the basis of the Fehling and the Benedict reactions, without need for Rochelle's salt or citrate for complexing. Tube heating on a low wattage hot plate is very useful, and very easily carried out by inserting the tubes in an empty glass beaker where the progress of the reaction is readily monitored, and also compared for various related reactions simultaneously.  I believe there is no need to heat in water baths or, in sand baths.

Some of the material in the chart was obtained from other sources.

Simple tests carried out with drops in vials, and on a plastic surface instead of test tubes. The results, in both cases can be preserved for frequent demonstrations. These tests appear very frequently in the recent IG examinations.

(a) Tests for (i) Nitrate(V) NO₃^- and (ii) ammonium ion NO₃^- & NH₄⁺ 

The tests are carried out with drops of reactants in small vials, warmed on a low wattage hot plate. The reactions proceed smoothly and most safely. NH₃ released is readily detected by inserting a wet strip of tissue paper to which is added a drop of phenolphthalein indicator. NH₃ can also be revealed by the white clouds observed when a strip of tissue paper with an added drop of concentrated HCl is exposed to the vapors at the vial openings.

(b) Reactions of iron(II) ion Fe²⁺ 

Small Vials (3ml capacity) are used as a substitute for test tubes. Reactants are added in drop, and heated where required on a low wattage hot plate. Water is added after the reaction for effective presentation. The vials are readily sealed by their hermitic standard rubber closures, and may be preserved as such for demonstrations, for a long time.

Same reactions can be carried out on a plastic surface. The products might be left to dry out, carefully warmed to hasten drying. They can also be preserved by covering with a transparent adhesive tape.  All other test tube reactions can be similarly performed in these vials, or on the plastic surface.

7. Element Reactions

(a) Burning magnesium

(b) Magnesium in acid

Adding a small sample of KMnO₄ solid followed by drops of HCl (conc) into the small vial and immediately stoppering the vial will generate Cl₂. The generated Cl₂ is safely kept for consecutive testing without need of a fume cupboard. This procedure drastically minimizes the release of Cl₂ in the environment. 

Test (i) Insertion of a test tissue paper strip wetted by drops of KI will release I₂ and causes the tip of the strip to be coloured intensely brown.

Test (ii) Dipping a test strip wetted by addition of a Fe²⁺ solution and a thiocyanate reagent, will cause the strip to acquire a very deep red colour. This is due to the oxidation of Fe²⁺ by Cl₂ to Fe³⁺ which complexes specifically with the SCN^- anion forming the characteristic red complex [Fe(SCN)(H₂0)₅]²⁺. 

Test (iii) A test strip moistened with NH₃(conc.) supported on top of the vial will cause the appearance of white clouds of NH₄Cl. The green gas Cl₂ has reacted with NH₃, releasing HCl, which reacts further with NH₃ to yield the observed white clouds.

Safety notes: The vial should only be briefly un-stoppered for testing. It must be kept stoppered always.  NaOH solution should be added to the vial before safe disposal , thus avoiding unnecessary release of any residual Cl2 to the atmosphere. 

8. Simple cell measurements - to measure Emf (E^ø)

Quick and simple way to test different electrode and electrolyte systems.

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