Transcript Physical properties

Chapter 3
• Physical and Chemical Properties
• Physical and Chemical Changes
Physical Properties
• Physical properties can be observed or
measured without changing the
composition of matter. Physical properties
are used to observe and describe matter.
• Physical properties include: appearance,
texture, color, odor, melting point, boiling
point, density, solubility, polarity, and
many others.
• NOT RELATED TO INTERACTION WITH
OTHER MATERIALS
What physical properties can you
observe?
Physical Properties of Magnesium
• Description:
– Grayish-white metal.
• Atomic Mass Average: 24.305 amu
• Boiling Point: 1363K 1090°C 1994°F
• Conductivity
• Density: 1.738g/cm3
• Enthalpy of Fusion: 8.95 kJ/mole
• Melting Point: 922K 649°C 1200°F
• Molar Volume: 13.97 cm3/mole
• Physical State (at 20°C & 1atm): Solid
• Specific Heat: 1.02J/gK
Chemical Properties
• Chemical properties of matter describes its
"potential" to undergo some chemical change or
reaction by virtue of its composition.
• It is quite difficult to define a chemical property
without using the word "change". Eventually you
should be able to look at the formula of a
compound and state some chemical property. At
this time this is very difficult to do and you are
not expected to be able to do it.
Chemical Properties
• “Reactivity” is really the only chemical property.
Anything that describes how a substance reacts
is a chemical property.
• For example hydrogen has the potential to ignite
and explode given the right conditions. This is a
chemical property.
• Metals in general have they chemical property of
reacting with an acid. Zinc reacts with
hydrochloric acid to produce hydrogen gas. This
is a chemical property.
Chemical Properties
• A chemical property of magnesium is that it reacts
with carbon dioxide producing an intense light.
Magnesium reacting with dry ice.
Physical Changes
• A physical change takes place without
any changes in composition. The same
element or compound is present before
and after the change.
Chemical Changes or Reactions
• Chemical changes result in one or more substances of
entirely different composition from the original
substances. The elements and/or compounds at the start
of the reaction are rearranged into new compounds or
elements.
• Magnesium reacts with oxygen from the air producing an
extremely bright flame. This is a chemical change since
magnesium oxide has completely different properties than
magnesium metal or oxygen.
• The atoms are rearranged - diatomic oxygen molecules
are split apart so that one oxygen atom combines with
one magnesium atom.
PHYSICAL CHANGE
Do not change the chemical
makeup of the changed material
CHEMICAL CHANGE
Result in a new material with a
different chemical makeup
being formed
Change only the physical
properties of a material
Change both physical and
chemical properties of a
material
relatively simple to reverse
very difficult to reverse
Look to be fairly simple changes
Look more dramatic
Not Likely to be accompanied by
changes in color, temperature,
state (unforced), or smell.
Often accompanied by change in
color, temperature, state
( unforced), or smell.*
Changes of State are physical changes
but can accompany a chemical change
• Physical Change
• Chemical Change
Precipitate
Precipitate
• A solid insoluble substance that forms when
solutions are mixed.
Distillation
• Distillation is used to purify a compound by separating it
from a non-volatile or less-volatile material. When
different compounds in a mixture have different boiling
points, they separate into individual components when
the mixture is carefully distilled.
Distillation
• Distillation is used to purify a compound by separating it
from a non-volatile or less-volatile material. When
different compounds in a mixture have different boiling
points, they separate into individual components when
the mixture is carefully distilled.
• Distillation is the process of heating a liquid until it boils,
capturing and cooling the resultant hot vapors, and
collecting the condensed vapors.
Distillation
• Distillation is used to purify a compound by separating it
from a non-volatile or less-volatile material. When
different compounds in a mixture have different boiling
points, they separate into individual components when
the mixture is carefully distilled.
• Distillation is the process of heating a liquid until it boils,
capturing and cooling the resultant hot vapors, and
collecting the condensed vapors.
• Mankind has applied the principles of distillation for
thousands of years. Distillation was probably first used
by ancient Arab chemists to isolate perfumes evidence
of which dates back to 3500 BC.
Distillation
• Distillation is used to purify a compound by separating it
from a non-volatile or less-volatile material. When
different compounds in a mixture have different boiling
points, they separate into individual components when
the mixture is carefully distilled.
• Distillation is the process of heating a liquid until it boils,
capturing and cooling the resultant hot vapors, and
collecting the condensed vapors.
• Mankind has applied the principles of distillation for
thousands of years. Distillation was probably first used
by ancient Arab chemists to isolate perfumes evidence
of which dates back to 3500 BC.
• In the modern organic chemistry laboratory, distillation is
a powerful tool, both for the identification and the
purification of organic compounds.
Fractional Crystallization
• Separates different solutes from a solution
based on differences in their solubility.
• A process by which a chemical compound is
separated into components by crystallization. In
fractional crystallization the compound is mixed
with a solvent, heated, and then gradually
cooled so that, as each of its constituent
components crystallizes, it can be removed in its
pure form from the solution.
What is the solubility
of KNO3 at 80ºC?
At what temperature
is the solubility of
KBr equal to
60g/100g H2O?
Example of Fractional
Crystallization
• The solubility of compounds changes with temperature,
and different compounds will respond differently to a
decrease in temp. For example, if compound A is
soluble at 30 to 35ºC, but compound B is insoluble at 30
to 35ºC, and if they are both soluble at 50ºC, then what
happens if you lower the temperature of a mixture of the
two solutions from 50 to 30ºC?
Example of Fractional
Crystallization
• The solubility of compounds changes with temperature,
and different compounds will respond differently to a
decrease in temp. For example, if compound A is
soluble at 30 to 35ºC, but compound B is insoluble at 30
to 35ºC, and if they are both soluble at 50ºC, then what
happens if you lower the temperature of a mixture of the
two solutions from 50 to 30ºC?
Answer: Compound A will still be in solution, but
compound B will have precipitated (crystallized).
Homework
• Chap 3 Worksheet 3-1