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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
?
Background information
Chemical substance
Any substance with a definite and constant chemical composition or multiple chemicals combined together in the same ratio
classify
Arrange objects in categories or groups according to similar characteristics
The best method
consider safety, accuracy, cost-effectiveness and speed
Physical properties
electrical/heat conductivity
aqueous, molten and solid state
Test: using a conductivity kit and checking the conductivity in the 3 above states
Positives
insight into the bonding type
solubility
Test: If the substance is a solid, putting the substance in water, stirring and observing whether it dissolves
Positives
Provides information on the bonding type as well as the physical properties
Limitations
Other than the substance's physical properties, the solubility is also affected by the stirring rate, time and pressure
melting/boiling point
Test: using a melting point apparatus or using a bunsen burner and measuring the time taken for the substance to melt
positives
can be used to generalise substances with high, moderate and low melting points
Limitations
The melting point appratus may not be available in a school setting
Appearance
includes
colour
luster
hardness
density
shape
Test: The physical characteristics of the chemical substance can be evaluated by observing it and noting down
qualitative observations
regarding colour, hardness and luster.
Limitatations:
Observing the appearance provides qualitative results that are subjective, can't be statistically analysed, and can't be generalised into groups. This means that observing physical appearance may not be a great method of classification.
Positives:
Qualitative research can complement and back up statistical evidence
malleability
Test: by hammering down a small quantity of the substance and noting down whether the substance breaks apart or bends
Limitations
If the substance is a liquid or gas at room temperature, the malleability can only be tested by lowering the temperature, which may not be achievable in the time span provided
Positives
The malleability provides insight into the bonding type as metallic bonds will bend while ionic and covalent compounds are brittle
Ductility
can't be tested in a school setting due to lack of equipment
chemical properties
includes
flammability
Test: place a quantity of the substance above a bunsen burner and measure how quickly it catches on fire using a stopwatch
Limitations
Random errors such as reaction time could limit the reliability of the results.
Definition
How quickly a substance can catch on fire and the intensity it burns with
acidity (ph level)
ph level test can be used to identify whether the substance is basic or acidic
Positives
provides a numerical approximation of the ph level
reactivity (with other substances)
toxicity
definition
Any properties that are evident during or after a chemical reaction
ability of a substance to react and form a new substance
chemical structure
Bonding
ionic
metallic
Testing
electrical conductivity test
solubility test
polarity test
melting point test
The physical properties of the substances can be used to identify the chemical structure an bonding
Limitations
Some substances have intermediate bonding characteristics, making it difficult to classify them into one category. For example, polar covalent compounds have some ionic characteristics due fractional charges.
some chemical substances could be a combination of different bondings
covalent
Pure substances
elements, compounds
atoms, molecules or lattices
organic vs inorganic
Most organic compounds contain both carbon and hyrdogen while inorganic compounds don't.
organic substances are derived from living beings while inorganic are derived from non-living components
Test: Flame test for carbon. If the substance burns and blackens, it contains carbon.
Positives
All substances are either organic or inorganic
Limitations
This only classifies the substances into two groups and does consider any other differences in their chemical structure
Phases of matter
solid
liquid
gas
testing
Observing the substance and its appearance
Limitations: The physical state of a chemical substance depends solely on the temperature. Increasing or decreasing the temperature ecan change the phase.
Positives: This method definitively classifies all chemical substances into 3 seperate groups