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What is the best method to classify a chemical substance - Coggle Diagram
What is the best method to classify a chemical substance
Variables
Independent Variable
In a practical, the independent variable is the variable that is being changed and the investigation will look at the variables impact on the results. The independent variable in the case of identifying and classifying unknown substance, will be the substance being tested as it is what is being changed each time.
Dependent Variable
In a practical, the dependent variable is the variable that is being measured and this will measure the impact of the changing independent variable on the results obtained. In this cases, the properties of each different unknown substance is measured in the hopes to find enough properties to be able to classify the type of bonding that is occurring within the substance.
Control Variable
For a experiment to have a limited quantity of errors, many things need to be kept constant which is known as a control variable. In this case some things that should be kept controlled is the batch of substance used, the equipment used, method of the test and quantity of substance used for each test.
Uncontrollable Factors
Machinery Errors
In this practical something that I believe would be uncontrol able is machinery errors. Many machines may be used to identify and classify a substance but one specific example may be a conductivity test. Unfortunatelly these kits may be prone to not effectivelly conducting due to factors such as being very old and possibly unused for long periods of time. This may then cause errors in the data as it may not give the accurate results in relation to electricity conductivity meaning that a substance may be able to conduct electricity, but the charge may be so low that the conductivity kit is unable to pick up on it. This cannot really be controlled unless a new kit is bought.
Chemical Impurities
Although all of the chemicals and substances may be used from the same batch and quantitty, there still may be some impurities. This cannot be controlled because these cannot necessarily be seen by the naked eye as these impurities will most likely be very minor. If it cannot really be seen, that means I will be unable to prevent it in the first making it uncontrolable with the amount of knowledge and equipment that I have available to me. However I still think that they are able to impact the results in some way because these impurities may be what leads the results to be different or even harder to understand. This may then lead to incorrect data to be collected.
Environmental Factors
Another factor that cannot be controlled in this investigation are just common environmental factors. This could include things like the humidity and temperature in the room where the tests are being conducted in. This cannot be controled throughout the practicle because even if things like the temperature can be attempted to control, there will always be some variation regardless.These factors can impact the results because the results obtained from the tests may be becauese of the environmental factors not the substance changing meaning it may be difficult to find the correct classification.
Variability In Samples
One factor that I did have the goal of keeping consistent was the batch of the same which I would use to conduct each of the test but something that I also find I cant really control, is the variability within this sample. This could happen during the creation of the sample where then, some of it may be mixed with another batch of the same substance which may have different properties in some scale and may react differently to the tests being conducted. This is not really something I can control since I am not the one creating the samples. This could impact the results because the substance could react differently to each test because of this variation.
Types of Chemical Substances
Ionic Compound
Ions are created when an atom either gives away an electron, or it takes one from another atom with the goal to create a stable octet. An ionic compound is created when an positively charged cation (metal ion) bonds with a negatively charged anion (non metal) . Because these ions are of opposite charges, they will attract and will thus form the ionic compounds
(Stewart, K, 2023)
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EXAMPLES
Sodium Chloride (NaCl)
Sodium Hydroxide (NaOH)
Potassium Iodide (KI)
Lithium Chloride (LiCl)
Covalent Molecular
In some cases, non-metals will bind with other non metals and this is when covalent bonding occurs. This is when the two atoms, instead of giving and taking like in ionic compounds, they will share their outer shell electrons to achieve a stable octet. Unlike a covalent network, these will not form lattices as these structures will exist as discrete molecules instead and the force holding it together is weaker
(Tutor Chase, 2023)
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EXAMPLES
Water (H2O)
Carbon Dioxide (CO2)
Methane (CH4)
Glucose (C6H12O6)
Covalent Network
A covalent network solid is a structure that is made up of a network of atoms that are covalently bonded together meaning that they will be sharing electrons to achieve a stable octet in their outer shell. They are also bonded in a 3D structure known to be a crystalline lattice
(Study Smarter, 2019)
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EXAMPLES
Diamond (C)
Boron Nitride (BN)
Silicon (Si)
Germanium (Ge)
Metallic Compound
The final main type of chemical bonding that commonly occurs, is metallic bonding which creates metallic compounds. A metallic bond occurs when two or more metals attempt to bind together. When this happensthe outermost electron shells will all overlap with a large number of neigbouring atoms and the electrons will be delocalised due to this. This process will leave behind positive ions which attributes to many of the metallic properties
(Encyclopaedia Britannica, n.d)
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EXAMPLES
Gold (Au)
Silver (Ag)
Copper (Cu)
Aluminium (Al),
Methods to Classify
Melting Point Test
Another property that is unique depending on the type of bonds taking place within a substance is the melting point of a substance. This test can be done by placing some of the substance on a watch glass over a Bunsen burner and see whether it melts and if so, how long it may take. This can further help to classify the substance because covalent molecules will have low melting points because it will take less energy to break the bonds while any other type will commonly have a higher melting points meaning it would take a long time or it may not melt all together.
Solubility Test
This test will also help to identify the type of substance being tested. This test would be very simple to conduct as the only thing that needs to be done is to take some of the unknown substance and then dissolve it in distilled water. This would then help as substances such as metallic compounds do not dissolve in water while ionic compounds do tend to dissolve in water. Covalent compounds can sometimes be a mix with it occasionally dissolving but in other scenarios not doing so. This test could then help with identifying the nature of this substance.
Conductivity Test
Each substance will also have different properties in relation to its ability to conduct electricity and energy. This can then be tested using a conductivity kit where when the substance is dissolved in water, it can be placed into the solution to see if it has the ability to conduct. If it is a metallic compound, it will not even need to be dissolved as they can conduct electricity when in the solid form. This test can then help to differenticiate between substances that are ionic or covalent because ionic can conduct electricity while covalently bonded molecules cannot do so.
Hardness Test
This is another test that could be done to help identify and classify different types of substances. This can first be done via observation by touching the substances to see if they form harder crystals or if they are soft and malleable to touch. This test can also be done by taking a hammer and smashing the substance and seeing what happens. If it is hard it will most likely shatter into smaller peices while if it is softer it may be more malleable and not break. This can help identify as covalent molecules and metllic compounds are often soft while ionic compounda and covalent networks are mainly found to be very hard.
Physical Observation
This is not exactly something that could be used in every case, but in some cases, physical observations can help to classify in some cases. For example, if the substances appears to be very shiny and looks metallic, it will most likely be a metallic compound meaning that there will be no reason to conduct any other test. This however alone will not be enough in the case of ionic compounds and covalent molecules as they both often will have some very similar appearances.
Properties of Chemical Substance
Ionic Compound
An ionic compound also has a set list of properties which is also different in comparison to other types of bonding. These types of substances will have a high melting and boiling point. This is because once again it requires a high quantity of energy to break all of the ionic bonds. These compounds are generally hard yet they are brittle as when smashed, ions of like charges will repel each other
(Chemistry Libre Texts, 2022)
. These substances cannot conduct electricity while solid but when molten or dissolved the compounds will separate into charged ions meaning energy can be conducted. It can also be dissolve in water mostly.
Covalent Molecular
These substances also have a set few properties which could maybe be used to help identify them. First, these substances will have relatively low melting points. This is because, unlike a network, a molecule will have a very small number of atoms meaning it will take less energy to break all of them
(BYJU, 2022)
. These are also commonly soft and in some cases for a similar reason of their bonds commonly being weakened leading to becoming somewhat flexible. Covalent molecular substances also cannot conduct electricity because it will not have any free charges when solid and they mainly cannot be completely dissolved in water either
(BBC Bitesize, 2019)
Covalent Network
Like every type of substance, a covalent network has a set of properties that is mainly unique to the type of bonding that is occurring. First, these substances will have a high melting point and this is because it will take a lot of energy to break all the covalent bonds in this network
(BBC Bitesize, 2013)
. They also will be hard due to their crystalline structure which keeps all of their electrons engaged in the bonds making it very difficult for the atoms to move
(Study Smarter, 2019)
. They also cannot be dissolved in water. These types of substances also do not conduct electricity because there are no free charges that can move and then conduct energy.
Metallic Compounds
Once again there are a few properties that are mainly unique to metallic compounds. These compounds will have a high melting point. This is because there is a very high force of attraction and it takes a very high quantity of energy to overcome this force. Metallic compounds are malleable and ductile that if smashed will not break and instead will be shaped differently and they can also be stretched into wires if needed. These compounds also have a metallic lustre in most situations meaning that they can be seen to have a shine to them if a light is shined onto them. Finally, metallic compounds can also conduct electricity and energy because of the delocalised electrons and their movement not being restricted
(BYJU, 2019)
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