Table to show the results obtained in the experiment:
The type of
bonding present in each substance:
- In the first substance there’s an ionic bond. Ionic bonds form hard crystal lattices. They normally have high melting and boiling points and they conduct electricity when they are dissolved in water.
The second and third ones are covalent bond. However, the second one is simple and the third one is giant.
- Simple covalent compounds contain only a few atoms held together by strong covalent bonds.They normally have low melting and boiling points and they don’t conduct electricity.
- Giant covalent structures contain a lot of non-metal atoms, each joined to nearby atoms by covalent bonds. They have high melting and boiling points and a variable conductivity.
- The fourth one there’s a metallic bond. Metallic bonds have high boiling and melting points and they are good conductors.
Table to show the expected results
Conclusion
As we can see in both tables, our results were fairly accurate. If we compare the first and second table we can se that the column of melting points had a few mistakes, as we said that Zinc had a medium melting point and after researching we found ou that it had a high melting point. Also, we said that Magnesium Chloride (Hexahydrate) wasn't soluble in acetone, however, it is fairly soluble. Finally, we also stated that Magnesium Chloride (Hexahydrate) didn't conduct enough electricity when dissolved because tha bulb didn't light up. After researching some information we discovered that yes, it conducts electricity.
We can see in question 2 that the expectation's table is correct as they match.
Evaluation
The method we used was fairly accurate, our results weren't perfect but they were good enough for us to see what it happens during the experiment. There are lots of things we can improve for the next time we do this experiment. Some of the most important are:
In the first place, the way we were meant to measure the amount of substance we needed (½ spatula) isn’t accurate as we can’t get exactly the same half a spatula of each substance as it will always be a bit less or a bit more each time. A solution to this, will be weighing (g) exactly the same amount of each substance, so that the experiment becomes more accurate.
Also, the results of the melting point aren’t accurate either, because we hadn’t heat all the substances for the same time, so this could have originated an error as the time we heated the substances was different every time. We removed the substance from heat when we thought it had melted or when we saw that it wouldn’t melt. The only thing the instructions in the method said was to wait approximately for 2 minutes as the maximum time(this is for high melting point), but we didn’t know the exact time because we weren’t using a watch or a stopwatch. We decided if it was medium, low or high by heating the substance and depending on the time it took (lots of time, some time or little time) to start melting, we then decided, but this isn’t accurate. So, as a solution, we could state beforehand a certain timing for each of the boiling points (low, medium or high), for example; low: from 0 to 50 seconds, medium from 51 to 100 seconds and high: from 101 to 150 seconds so that then, when we start heating up the substance, we can see by using a stopwatch the exact time it takes to start melting, and then classify it into one of the boiling points, depending on the time it took for it to start melting.
Furthermore, the way we tried to dissolve the substance in water wasn’t precise because we might have stir it with different forces each time and in different ways and sometimes stirring is not enough. As a solution we could use a machine which mixes the substance with the water, which is much more accurate than what we did.
Moreover, the light bulb or other components of the circuit, might have been a bit broken or didn't work well enough, so maybe the substance was a conductor but because of this, we wouldn't be able to know. As a solution, we could make sure everything works okay with something we are 100% sure is a conductor before the experiment. There might have also been not enough amount of each substance to light the bulb up, because even though it is a conductor there might have not been enough of any of them to light it up, so we could get more of each substance so that there is enough to light a small bulb up.
Finally, each time we lit and turned off the bunsen burner because we wanted to melt something, there wasn’t the exact same amount of heat coming off of it, so this could have originated a problem because maybe some have a higher melting points than others, but because of this, we thought that they had a lowe point. So, this could be solved if you keep it lit up on a corner of the lab so that anyone gets burnt, but it still emits always the same amount of heat.
We could have done more tests to get more precise and reliable results but we didn’t have time to do it. To finish, there is also a thing that could be the cause of a mistake: In our group, we took turns to fill up the test tube with 5 ml of stirred water or acetone. Maybe one of us, didn't fill it with exactly 5 ml. Another thing that makes our experiment imprecise is that we used the same volumetric pipet throughout the experiment, so if a bit of stirred water stayed there and mixed with acetone or vice versa it could have make our results to vary. A solution to this is to take a different volumetric pipet each time or if there are not enough, clean it and dry it before using it again.
Bibliography
- Bbc.co.uk,. (2015). BBC - GCSE Bitesize: Covalent bonding - giant covalent structures. Retrieved 9 October 2015, from http://www.bbc.co.uk/schools/gcsebitesize/science/add_aqa_pre_2011/atomic/differentsubrev3.shtml
- Bbc.co.uk,. (2015). BBC - GCSE Bitesize: Metal properties and uses. Retrieved 9 October 2015, from http://www.bbc.co.uk/schools/gcsebitesize/science/add_ocr_pre_2011/chemicals/metalpropertiesrev1.shtml
- Deshpande, A. (2015). Properties of Graphite. Buzzle. Retrieved 9 October 2015, from http://www.buzzle.com/articles/graphite-properties.html
- Npi.gov.au,. (2015). Zinc and compounds | National Pollutant Inventory. Retrieved 9 October 2015, from http://www.npi.gov.au/resource/zinc-and-compounds
- Scbt.com,. (2015). Magnesium Chloride, Hexahydrate | CAS 7791-18-6 | Santa Cruz Biotech. Retrieved 9 October 2015, from http://www.scbt.com/datasheet-203126-magnesium-chloride-hexahydrate.html
