Unit 1.0 Flashcards
Difference between physical and chemical properties
Physical property can be
* observed or measured without forming a new substance(colour,density)
VS
* chemical properties describes how a substance reacts with another substance when forming a new substance ( combustibility, iron
rusting, glucose and yeast
fermenting, TNT exploding)
Chemical property
- the ability of a substance to react with
another substance and form one or more new
substances - are exhibited during a chemical reaction
what are examples of Chemical Properties:
- reactivity with other substances
- combustibility
- stability
- toxicity
Reactivity with
Water
➢ Calcium carbide
(a compound)
combines with
water to form
acetylene gas
(C2H2
)
➢ CaC2 + H2O
→ C2H2 +
Ca(OH)2
Cavers use acetylene gas as a
light source.
Reactivity with
Oxygen
➢Aluminum metal reacts
with oxygen to
produce
aluminum oxide
➢ Al + O2 →
Al2O3
Aluminum oxide protects these grain storage bins from coroding
Reactivity with acids
➢ Baking soda
(sodium
bicarbonate) reacts
with vinegar to
produce carbon
dioxide gas (CO2
).
➢ NaHCO3 +
CH3COOH →
CO2 + H2O +
Na2CO3
In baking, carbon dioxide gas makes the dough rise
reactivity with another pure substance
➢ Sodium and chlorine
(two highly reactive
elements) combine to
form sodium chloride
(salt).
➢ Na + Cl2 → NaCl
Knowing how pure substances react help chemists to create
new products.
Chemical Properties of Common Gases
- hydrogen gas (H2)
- Water vapour** (H2O)**
- Carbon dioxide** (CO2) **
- oxygen gas (O2)
how to test to see if you can prouduce hydrogen gas (H2)
bring a flaming splint close to the top of a slanted test tube
containing the gas. Hydrogen gas will ignite and burn rapidly down
the test tube, producing a “whoop” or “pop” sound.
how to test to see if Water vapour (H2O) is produced
with a piece of cobalt chloride paper. The blue paper will turn pink in the presence of water.
how to test and see if oxygen gas (O2) is being produced
involves bringing a glowing splint (one
that is no longer flaming) into the slanted test tub. If oxygen gas is
present, the splint will re-ignite.
Combustiblity
- the ability of a
substance to burn in
air - e.g. propane (C3H8
) is
combustible and
reacts with oxygen
(O2
) in air to release a
large amount of heat
* C3H8 (g) + 5 O2 (g) ⎯→
3 CO2 (g) + 4 H2O(l
H = -2220 kJ
Stability
- the ability of a substance to
remain unchanged - how easily the substance breaks
down or decomposes - more stable substances take
longer to decompose - for a chemical to be useful, it
must have enough stability to
exist long enough to carry out its
required function
Toxicity
- the ability of a substance to cause harmful
effects in plants and animals - almost all chemicals are poisonous at high
enough concentrations - e.g. you need oxygen to breathe, but too
much will kill you
facts about toxicity
- toxicity is reported as a LD50 value
– the dose required to kill 50% of the exposed
population - e.g. only 0.000 000 001 g/kg body mass of
Clostridium tetani is needed to kill a person!
2 types of toxicity
- acute toxicity
– severe and sudden toxicity
– Eg. Iron (Fe) - Iron overdose has been one of the
leading causes of poisoning deaths in children
younger than 6 years. - chronic toxicity
– long-developing toxicity due to prolonged exposure
over time
– Eg. Lead (Pb) - there is a wide range of neurological
effects associated with lead exposure, some of which
may likely be irreversible.
acute toxicity
– severe and sudden toxicity
– Eg. Iron (Fe) - Iron overdose has been one of the
leading causes of poisoning deaths in children
younger than 6 years.
chronic toxicity
– long-developing toxicity due to prolonged exposure
over time
– Eg. Lead (Pb) - there is a wide range of neurological
effects associated with lead exposure, some of which
may likely be irreversible.
2 chemical properties that are linked
stability and toxicity
Stability and toxicity
- stability and toxicity are often linked
- e.g. DDT is stable, thus it does not easily break
down and thus bioaccumulates (stability) and
biomagnifies (toxicity).
Physical Properties
– Can be observed without changing a substance
into another substance.
* Boiling point, density, mass, volume, etc.
Chemical properties
– Can only be observed when a substance is
changed into another substance.
* Flammability, corrosiveness, reactivity with acid,
etc.
Evidences of chemical change
- gas formation
- precipation formation
- odour change
- energy production
Gas formation
- usually observed as bubbles
