In an experiment, iron filings were heated with sulphur powder to obtain iron sulphide. If the
mass of iron filings taken were 2 g and the mass of iron sulphide formed was 3 g, what was the
mass of sulphur powder used for the experiment?
Answers
Answer:
Prepare a mixture containing iron powder and sulfur powder in the ratio 7:4 by mass. Do this by weighing out 7 g of iron powder and 4 g of finely powdered sulfur onto separate pieces of filter paper (or use weighing boats). Mix the two powders by pouring repeatedly from one piece of paper to the other until a homogeneous mixture (by appearance) is obtained.
Note the appearance of the pure elements and the mixture. Demonstrate that iron can be separated from the mixture by physical means. Do this by wrapping the end of a small bar magnet in a paper tissue or cling film, and dipping it into a teaspoon sized heap of the mixture on a watch glass. The iron will be attracted, but the sulfur remains on the watch glass.
Place about 2 g of the mixture into a borosilicate test tube.
Insert a plug of mineral wool (mineral fibre) into the mouth of the test tube. Clamp the test tube as shown in the diagram.
Heat the powder mixture at the base of the test tube – gently at first and then more strongly (use a blue flame throughout). Heat until an orange glow is seen inside the test tube. Immediately stop heating. Let the students see that the glow continues and moves steadily through the mixture.
Allow the test tube to cool down. At this point the students could carry out their own small scale version of the reaction.
Once cool, it is possible to break open the test tube to show the appearance of the product, iron(II) sulfide. The test tube can be broken open using a pestle and mortar. It is advisable to wear protective gloves.
It may be possible to show that the product, iron(II) sulfide is non-magnetic. However, this is not always successful. It has been suggested that using a very weak magnet is advisable.
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A diagram of the apparatus st-up for the iron and sulfur experiment