Analía Bellizzi – Chemistry Classes

Ronald Reagan Senior High School

Pure substances, Mixtures and Compounds

Elements, Mixtures, and Compounds

Purpose of the lab

To determine the properties of pure substances, mixtures and compounds

Materials

    • Safety goggles
    • Paper (filter paper works well)
    • Balance (digital or triple-beam)
    • Sulfur powder
    • Iron powder
    • Scoop
    • Hand lens
    • Magnet
    • Plastic bag
    • Test tube
    • Test tube clamp
    • Bunsen burner
    • Striker
    • 250-mL beaker
    • Forceps

Procedure

    1. Place a piece of paper on the balance and observe its mass. Scoop out sulfur powder onto the paper until you have added 3 g of the powder. Remove the paper and sulfur powder from the balance.
    2. Use the hand lens to help you observe properties of the sulfur (color and size and shape of the particles). Record your findings in the data table.
    3. Put the magnet inside the plastic bag (so that any particles attracted to the magnet can be easily removed). Run the magnet over the top of the sulfur powder to see if there is any interaction. If any particles are attracted to the magnet, hold the particles over the paper and carefully remove the magnet from the plastic bag so that the particles will fall back onto the paper. Record your findings in the data table.
    4. Keep the sulfur powder on the paper and place it to the side.
    5. Place a new piece of paper on the balance and scoop out 5 g of iron powder. Remove the paper and iron powder from the balance.
    6. Use the hand lens and the magnet to repeat steps 2 and 3 with the iron powder. Record all observations in the data table.
    7. Make a mixture of the two powders together on one piece of paper. Use the scoop to mix them up and make sure that the particles are evenly distributed.
    8. Repeat steps 2 and 3 for the mixture of iron and sulfur particles. Again, record observations in the data table.
    9. Put cold water in the beaker until it is about half-full and then place the beaker to the side.
    10. Carefully pour the mixture of iron and sulfur powders into the test tube.
    11. Light the Bunsen burner and make sure you get a nice flame. (Have your teacher check it if necessary.
    12. Hold the test tube with the test-tube clamp and place it in the flame. (Make sure the mouth of the test tube is not pointed at you or anyone else.) Move the test tube around in the flame to make sure all of the contents are getting heated evenly. Continue this for approximately 2 minutes or until no more changes are occurring in the test tube.
    13. Shut off the gas to the Bunsen burner and quickly place the test tube in the beaker. The cold water should cause the test tube to break. If the test tube does not break, call your teacher over and have her break it for you.
    14. Do not touch any of the pieces in the beaker. Use the forceps to pull the substance from the test tube out of the water and place it on a piece of paper.
    15. Repeat steps 2 and 3 for the compound that was made from the sulfur and iron powders. Record all observations in the data table.

Data Table

 

Physical Properties

Sulfur Powder

Iron Powder

Iron-Sulfur Mixture
(prior to heating)

Iron (II) sulfide compound
(after heating)
Color
Shape of particles
Size of particles
soluble in water?
soluble in water?
Interaction with magnet

Analysis Questions

 

  1. What is the chemical symbol for sulfur?
  2. What physical properties of Sulfur can you observe? color, state of the matter, odor, magnetism, etc.
  3. What is the chemical symbol for iron?
  4. What physical properties of Iron can you observe? color, state of the matter, odor, magnetism, etc.
  5. How does sulfur react in the presence of a magnet?
  6. How does Iron react in presence of a magnet?
  7. How does the iron/sulfur mixture react in presence of a magnet?
  8. What is the chemical symbol for iron sulfide?
  9. what are the properties of Iron Sulfide you can observe?
  10. how do Iron and sulfur mixture differ from iron sulfide?

This is for your teacher. do not attempt to do this by yourself

Demonstration

a 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.

b 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.

c Place about 2 g of the mixture into a borosilicate test-tube.

d Insert a plug of mineral wool (mineral fibre) into the mouth of the test-tube. Clamp the test-tube as shown in the diagram.

 

 

e 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.

f Allow the tube to cool down. At this point the students could carry out their own small-scale version of the reaction.

g 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.

h  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.
Class practical

a Students should be provided with pre-prepared ignition tubes containing the iron–sulfur mixture and a mineral wool plug.

b Using suitable tongs or test-tube holders, the iron-sulfur mix in the tube should be heated until the mixture just starts to glow. Bunsen burners should then be turned off.

c The reaction tubes should be left to cool on the heat resistant mat. It may be sensible to get the students to place all their used reaction tubes onto one heat resistant mat set aside for this purpose (e.g. on the teacher’s desk or in a fume cupboard).

Teaching notes

On heating the reaction mixture, the sulfur melts and reacts with the iron exothermically to form iron(II) sulfide. The mineral wool plug in the mouth of the test-tube prevents sulfur vapour escaping and possibly catching fire. If, despite all precautions, the sulfur vapour does ignite, students must be trained to extinguish it by placing a damp rag firmly over the mouth of the tube.

The signs that a chemical reaction occurs are: the glow, and the fact that a new substance (black iron sulfide) is formed which cannot be separated by using a magnet. Although see note h in the Procedure section.

This may be an opportunity to introduce or reinforce the ‘rule’ that if only two elements are combined together, the name of the compound ends in ‘-ide’.

Health & Safety checked, 2016

Credits

This Practical Chemistry resource was developed by the Nuffield Foundation and the Royal Society of Chemistry.

© Nuffield Foundation and the Royal Society of Chemistry