What is the best method to classify a chemical substance?
Variables
Methods of Testing
Limitations
Background Information
Appearance
Physical
Odour
Conductivity
Solubility
Brittility
Ductility
Malleability
Lustre
Substance given is unknown
Limited Amount of UNKNOWN substance
Methods of testing may not be done in controlled environment (Extraneous Variable)
Independent
Dependent
Controlled
Extraneous
Risk Assessment
Brittility Test: Hammer use (Injury-Prone)
Conductivity Test: Short Circuit/Shock Possibility
Bunsen Burner Used: Burn Hazard
Odour: May be strong and unpleasant (Can be a biological hazard)
Lustre Test (Sand-Paper) can cause Scraping Hazard
Structures (In Bonding)
Ionic Structure
Metallic Structure
Covalent Network Structure
Covalent Molecular Structure
Type of Substance Tested: 5 Substances tested (Differing Properties = Different Subtance). The variable being changed is that we are using a Substance unknown (A-E) each time, and so only one of these should be used for each test at one time, and once all tests are done and data collected, cycle through the 5 unknown substances
Type of Equipment Used
Methods of Testing (ALL Substances get tested with the same Methods)
Same amount of substance used for each test
Same Equipment (but refurbished use) for each test; same exposure to all equipment but should not come in contact with any other chemical substance (that it is not supposed to), E.g. A beaker with Substance A should not be used [without proper sanitation] to then be tested with Substance B.
Results from Methods = Dependent Variable (Measured Data)
Observed and Numerical Data obtained from "Methods of Testing" below = Dependent Variable/s
Environment Tested
Any residue of substance that resides on equipment (E.g. Rust or Soot that cannot be removed)
Safe disposal of Chemical (They are unknown and so could damage certain surfaces)
Electrostatic Force of Attraction between oppositely charged particles, forming a crystal lattice structure
Electrons GAINED and LOST
Metals and Non-Metals
Electrostatic Force of Attraction between Metal Cation and Delocalised Electron
Metals Only
Uniform throughout and Strong
Factors Affecting Key Substance Measured (Errors)
Atoms covalently bonded within a large, 3D network of layers
Type of Bond Substance Has
Different Type of Bond = Different Properties
Properties
HIGH Melting and Boiling Points
Hard and Brittle
Conductive in Liquid/Molten BUT not solid state
Crystal Lattice Structure
NOT ductile or malleable
Non Metals Only
Sharing of Electrons
Properties
Soft/Flexible
LOW Boiling and Melting Points
Poor Conductors of Heat and Electricity
Less soluble than ionic
Dissociates/dissolves well in water
Solid at Room Temp.
Gas, Liq, or Solid at Room Temp.
Properties
HIGH Melting and Boiling Points
Hard/Strong/Highly Dense
Good Conductor of Elec. and Heat in ALL states
Malleable/Ductile
Very Strong Metallic Lattice (Metal Cations and Sea of Delocalised Electrons)
Lustre
Atmospherical Conditions (Systematic)
Room Temp.
Humidity
Wind Draft
Faulty Equipment (Systematic)
Conductivity Tester can be electronically faulty or short circuited
Coated Equipment (E.g. Rusted Metallic Objects)
Fragile Apparatus (Can crack, damage, even possibly coated by substance, causing skewed results)
Beakers use, therefore glass shard hazard (Cutting hazard), if BROKEN
Tarring (Scale)
Continuous 3D Lattice of layered atoms, covalently bonded, usually of the same element.
Properties
HIGH Melting and Boiling Point
Hard/Brittle
Generally DO NOT conduct electricity (Exception Graphite)
Can conduct heat to limited extent (based on substance)
Reference List:
Lumen Learning (2014). Solids | Introductory Chemistry – 1st Canadian Edition. [online] Available at: https://courses.lumenlearning.com/suny-introductorychemistry/chapter/solids-2/#:~:text=Generally%2C%20covalent%20network%20solids%20are,100%20times%20less%20thermally%20conductive. [Accessed 31 Oct. 2023].
Nagwa (2020). Network Covalent Structures. [online] Available at: https://www.nagwa.com/en/videos/838187643063/#:~:text=Network%20covalent%20structures%20have%20consistent,the%20presence%20of%20delocalized%20electrons. [Accessed 31 Oct. 2023].
Chemistry LibreTexts (2015). 12.5: Network Covalent Solids and Ionic Solids. [online] Available at: https://chem.libretexts.org/Bookshelves/General_Chemistry/Map%3A_General_Chemistry_(Petrucci_et_al.)/12%3A_Intermolecular_Forces%3A_Liquids_And_Solids/12.5%3A_Network_Covalent_Solids_and_Ionic_Solids [Accessed 31 Oct. 2023].
Nagwa (2020). Comparing Molecular Solids and Covalent Networks. [online] Available at: https://www.nagwa.com/en/videos/219181717247/#:~:text=Molecular%20solids%20have%20low%20melting,together%20by%20weak%20intermolecular%20forces. [Accessed 31 Oct. 2023].
University of North Carolina (2023). Measurements and Error Analysis. [online] Available at: https://www.webassign.net/question_assets/unccolphysmechl1/measurements/manual.html [Accessed 31 Oct. 2023].
US NRC (2023). What is a Chemical ? [online] Available at: https://www.nrc.gov/reading-rm/basic-ref/students/science-101/what-is-a-chemical.html [Accessed 31 Oct. 2023].
Google Sites Y10 Spec Chemistry IB E-Textbook
PPT Information Provided on 10 Spec Chem Google Classroom
Halide Test
To test for metallic structure as only Metallic structures consist of lustre. (E.g. Sand Paper)
Ionic substances dissociate in water to conduct electricity (and so can be tested to see if Substance X as an aqueous can conduct).
Certain lattices can be determined from their appearance to narrow down the search (E.g. Ionic = Crystal Lattice, metallic structures have lustre and smoothness, etc)
How brittle or hard something is can determine the type of compound (e.g. Ionic compounds such as salt, is brittle. Graphite is brittle and leaves black residue on surfaces)
Only certain structures can conduct. Ionic can conduct in solution or as molten. Covalent structures, in general, cannot conduct (Exceptions apply)... EXPAND
To test whether a certain substance fits with the Halogen Group, to narrow the search
All these Methods are used to narrow the substance to a certain structure and to the name of the given "X" Compound (if necessary). Therefore best method is to work the way down through these list of experiments to identify properties of "X" substance, to then classify substance.
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Conductivity: Testing meter illuminating or not
Brittiliy: Whether become powder or not
Halide Test: Identify what precipitate forms to identify substance
Physical Properties: Qualitative Observative Measurements
Substance Chemical Change in exposure to atmosphere
What is a chemical substance?
Certain form of matter (Element, Compounds, Mixtures) that have a certain constant chemical composition with define characteristic properties.
How to identify?
Determine what characteristic a certain substance has (through Methods) to identify how they are composed and how they react, to narrow down individual properties to structures (E.g. An Ionic substance can ONLY conduct as solution and molten, Covalent cannot conduct at all in most cases and Metallic CAN conduct in all states, so there is a noticeable characteristic difference that can be used to narrow what substance "X" can be).
Limited type of methods available (E.g. pH Test, Halide Test, etc, can all be implemented to identify substance but we are restricted to certain experiments we've already done)
Protective Gloves to reduce chance of skin being damaged
Proper PPE (Apron, Gloves and Eye Protection) as well as careful handling of heated equipment
Use tissue paper to wrap substance + use hammer on floor to avoid damage to person and surface. Keep at safe distance before testing.
Test the equipment with a control (such as tap water or distilled water) and check result. Also check for any damage. Ensure equipment is accurate and SAFE before using for unknown substance
Take whiffs of substance at safe distance, and avoid smelling too close to substance. If uneasy, then STOP procedure immediately.
Ensure safe practice and handling of glass materials. If it breaks, have dustpan, protective gear (gloves) and glass disposal unit on standby for safe broken glass handling and disposal.
Testing
Test melting/boling point to understand how high or low it may be
If suspected of excpetion such as graphite, then test for conductivity and brittility.
OTHER THAN EXCEPTION, identify inability to conduct either as solid or liquid or aqueous.
Testing
Dissolve then test conductivity as ions should be free in ionic substance and should conduct
Test brittily
Test MP/BP
Test brittility (Shouldn't be brittle)
Testing
Test its flexibility and softness
Conductivity Testing
Melting and Boiling Points
Same tests as COVALENT NETWORK (except check for the difference in MP/BP, physical brittility and solubility to evaluate)
Testing
Visual physical properties (Lustre, smooth, hard and NOT brittle)
Conductivity (Should conduct in ANY state)
Melting and Boiling Points
Use hammer to see if it breaks or merely indents/changes shape
Time Limit (Only Approx. 1 Lesson to Identify Chemical Substances)
Observative Results on Physical attributes, Odour, etc
Amount of Substance used for each test (Random)
Different amounts can vary the results of each test and we are limited so not every test can have a controlled amount (E.g. I may need more for a conductivity test to actually detect conduction as opposed to brittility in which I only need a few particles to test if they turn into a powder). This variable may be considered extraneous.
Hammer test to see if substance deforms or changes shapes (Meaning it is metal as only metal is malleable. Other structures are brittle and would shatter.
Hammer test or if thin enough, roll with equipment, to see if substance deforms or changes shapes (Meaning it is metal as only metal is malleable. Other structures are brittle and would shatter.
(E.g.) Iron Oxide had Unpleasant Odour when reacting with HCI, therefore using research, the reactant and odour can identify the derivative of the substance tested.
(Ionic Compounds as well as certain covalent compounds are brittle, however metals ARE NOT) so by beating (with hammer or hard object), test if substance shatters or not.
First Aid
Have proper cleansing and decontaminating wipes to clean any wounds that may occur
Bandaids (Gauze, Crepe, Adhesive)
Tweazers
Cast