Practical: Comparing Element, Compound and Mixture

This is my first Chemistry practical lesson since I was absent during last week's practical. So I was actually very excited for the session!

-Focus Question: What are some common characteristics of mixtures and compounds that can be used to distinguish them?

-Hypothesis: Mixtures can be separated by physical means but compounds cannot be separated by physical means.

-Conclusion: My hypothesis is correct! (but not complete)
To add on, the substances in a mixture can be mixed in any proportion. No energy change takes place when a mixture is formed. A mixture has the properties of its constituent substances.
On the other hand, properties of a compound have different physical properties from its constituent substances. A compound cannot be separated by physical means. A chemical reaction takes place when a compound is formed when there is energy change.

WHAT WE DID
(here I took pictures of our investigation in progress with my lousy camera phone! :P)

Here are some of the materials we used for the whole investigation.

Shown in the picture on the left are iron fillings, sulfur powder, thongs, test tubes, crucibles, filter paper, magnets and bunsen burner.

We also used a tripod stand for heating and a stirrer for stirring the mixture and compound with water.

Of course, we had to put on our safety goggles (shown in picture) as a safety measure.





PART A:
We recorded our observations of the two substances, iron fillings and sulfur powder after putting them on a piece of filter paper.
The iron fillings appeared silvery-grey while the sulfur powder appeared bright yellow.
Then, we mixed the two substances together.
We then felt the bottom of the filter paper to feel if it was warm but it was just cold.
Next, we tried to separate the iron fillings from the mixture using a magnet and it worked!
We then put the mixture into a test tube filled with water. What we observed was that both substances were insoluble in water and that the sulfur powder is suspended near the surface of the water while the iron fillings sank to the bottom of the test tube. This was because the density of iron fillings is higher than that of sulfur powder.

Sulfur and iron.

Mixing them! 

Iron fillings being attracted by the magnet at the bottom of the filter paper.

PART B:

We mixed one spatula of sulfur powder and half a spatula of iron fillings in a crucible. Then, we set up the bunsen burner and left the crucible covered with a lid to heat for 10 minutes under a strong flame. As I missed last week's practical, I did not know how to use a bunsen burner at all and I was pretty lost. Luckily my partner patiently explained to me the steps involved in setting it up, making me feel much more confident of using it. 

After heating, we allowed it to cool, and we got a black hard solid substance in the crucible. 

The compound did not separate iron from sulfur when we used a magnet. Neither did the two constituent substances separate when placed into the test tube with water. The black compound was also insoluble in water. 

Heating up the mixture under a strong flame

After 10 mins of heating

Along the lesson, I came to learn that this compound is known as iron sulphide and I actually googled for it's chemical formula, just out of curiosity. So it's FeS. Then I got really confused. I came across another term, iron sulphate. I have not the slightest idea which is which and how they are different but I think I will probably find out soon. 

Extra stuff I've learnt also include that adding too much iron will cause the final compound to have excess iron fillings. 

Some reflections I have for the day...

I feel that reading instructions carefully is very important. Another group in class added one spatula of iron fillings into the crucible instead of the half spatula which was specified. Although it was good that everyone could learn something out from their mistake (about how the final compound would be affected if there were more iron fillings), it could be really dangerous if there was a harmful chemical reaction that would take place whenever there were excess substances. I also think that I should be more accurate and alert while doing the experiment. While setting the crucible to heat, I did not take note of the time we started heating but luckily, we quickly realised that we forgot to watch the time and tried to start counting from where we left off. I think it's always better to be accurate and precise.

I've learnt so much from such a simple science practical and I could finally try it out for myself to make compounds and mixtures. I'm looking forward to the next science practical!