Transcript seperation of mixtures - personals.okan.edu.tr

GENERAL CHEMISTRY
Sources for the lecture:
1. Author: Petrucci & Harwood
General Chemistry: Principles and Modern
Applications
2. Author: Mortimer;
Modern University Chemistry
Contents:
Topic 1: Matter: Properties & Measurement
Topic 2: Atoms and The atomic Theory
Topic 3: Electron Structure of Atoms
Topic 4: Chemical Compounds
Topic 5: Chemical Reactions
Topic 6: Gases
Topic 7. Thermochemistry
TOPIC 1: Matter—Its Properties
and Measurement
What is the matter?
• Matter: Everything that has a certain mass and
volume can be defined as matter.
• The matter can be defined as any object which
can be perceived through our 5 senses (water,
soil, plants, air, etc.). On the other hand, we can
observe some substances(the particles which
come out as a result of radioactive disintegration
or cosmic radiation) only by means of some
instruments .
• The matter which has a certain shape and is
described within this concept is called body.
The intensive(distinguishable)
and extensive(common)
characteristics of matter
• EXTENSIVE PROPERTIES:The common
characteristics of matter depend upon the
amount of the substance (mass, volume, ).
• INTENSIVE PROPERTIES:The
distinguishable properties do not depend
upon the amount of matter(density, boiling
point,melting point, solubility, expansion,
conductivity,
elasticity,
odor,
color,
hardness)
Physical and Chemical Properties
of Matter
• Physical Properties: These are the ones that a
sample of matter shows without changing its
composition Examples:
•Melting point
•Freezing point
•Density
•Color
• Chemical Properties: These are described as
the abilities of a sample of matter to undergo a
change in composition under stated conditions
• Example
• :Whether the matter is active or not, can be combusted with the
oxygen or not, can react with acids and bases or not, etc.
STATES
OF
MATTER
(Deposition)
SOLID↔ (melting/freezing) ↔ LIQUID↔ (evaporation/ condensation) GAS
(sublimation)
Transactions during the change from the solid state to
gas state:
•
•
•
•
•
•
•
•
The distance between the molecules increases
The kinetic energy of the molecules rises
The tensile forces between molecules decline
The mass remains unchanged
The chemical property remains unchanged
The physical property changes
The density generally falls down
The entropy rises
State of Matter
SOLID
LIQUID
GAS
The 3 Phase Transitions of water in
Temperature verse Time plotted Graph
At 1 atm. pressure
( Ek = Kinetic Energy Ep = Potential Energy )
Matter
Substances
Compounds
Seperation by physical
changes
Elements
Homogeneous
Decomposition by chemcial changes
Mixtures
Heterogenous
Elements - Compounds
• An element is a substance comprised of a
single type of atom (mercury, gold, etc.).
There are overall 111 well known
elements existing in the world. These are
listed in the periodic table. The elements
which are listed in the table after 92.
element Uranium, have come across as a
result of nuclear reactions,whereas the
others are naturally present.
• A compound is a substance in which
atoms of different elements are combined
with one another(e.g water,salt).
Mixtures
• Homogenous Mixtures are uniform in
composition and properties throughout a given
sample, but the composition may vary from
one sample to another. Examples:
• air : gas-gas mixture
•
•
•
•
Salty water :solid-liquid mixture
Beverage gas: liquid mixture
Alcohol-water: liquid-liquid mixture
14 carats gold : solid-solid mixture
Mixtures
• Heterogenous mixtures are mixtures in
which the components seperate into
distinct regions.Thus, the composition and
physical properties vary from one part of
the mixture to another.
• Examples: Salad dressing
• A slab of concrete
• The leaf of a plant
• Olive oil-water
Example for heterogenous mixtures: Iron powder
and sand mixture
PROPERTIES OF MIXTURES
1.They can be mixed up at any ratio
2. The substances constituing the mixture do not
lose their own characteristics
3. The properties of a mixture relies on the ratio of
the substances making up the mixture.
4. They can be seperated into their components by
physical methods
5. They do not have any formula
6. They can be either homogenous or heterogenous
PROPERTIES OF COMPOUNDS
1. There is a certain ratio between the substances
constituing the mixture.
2. The substances which are being a part of the
compund lose their own properties
3. Compounds can be seperated into their
components by some chemical methods.
4. The melting and boiling points of the
compounds are constant.
5. They have a specific formula
6. They are homogenous.
SEPERATION OF MIXTURES
The process of recovering the substances induvidually building
up a mixture has been defined as seperation or purification. The
seperation methods are modified on the basis of the different
properties of components . The seperation techniques can be
divided into two headlines:
A- SEPERATION OF HETEROGENOUS MIXTURES BY
PHYSICAL METHODS
B-SEPERATION OF HOMOGENOUS MIXTURES BY
PHYSICAL METHODS
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gözlemlersiniz.
A) SEPERATION
PHYSICAL METHODS
OF
MIXTURES
BY
1. Seperation by means of electricity
If an ebonite or plastic bar is rubbed against a piece
of material made of wool, it is charged electrically. .
When this electrically charged bar has been brought near
to a mixture made up of sulphur and sand , it is observed
that it draws the sulphur powder,whereas it does not
draw the sand . What it remains after the seperation is
just sand.
This method is applied only for small amounts. It is
non-convenient for the industrial use. We can seperate
some mixtures from each other by making use of the
different induction capability of each matter.
2. Seperation by a magnet
The substances such as iron,cobalt, nickel can be drawn
by a magnet,whereas the others such as sulfur, salt,
copper, gold are not affected by a magnet.When a
magnet is closed up to the mixture of sulphur and iron
powder, the iron particles are seperated by the magnet.
(Figure1.1).
Figure 1.1 When a magnet is closed up to the mixture of
sulfur and iron powder, the iron particles are seperated from
the sulfur powder.
2. Seperation by a magnet
By means of this method the pins or clips
made of iron can be seperated from the pile of
papers. Therefore , it is used in the paper
industry.
Those substances which can be induced
magnetically can be seperated from the other
substances which do not show this manner. As
a result, this method is generally suitable for
solid-solid mixtures.
3. Floating and Precipitation(Seperation by the
difference of density)
• How can we seperate in a mixture the iron powder
and the pellicle components?
• In order to seperate these components, water that is
not reactive with the components is added into the
mixture.
Figure 1.2. Precipitation process(k,k: pellicle, water : in
the middle of the mixture and iron powder: at the bottom
of the container
3. Floating and Precipitation(Seperation by the
difference of density)
• While the iron powder which has a
greater specific density than water is
sinking at the bottom of the container, the
pellicle which has a smaller specific
gravity than water is collected over the
surface of water (Figure 1.2). With the help
of a spoon, the pellicle can be removed
from the mixture. As the water is filtered
slowly, the iron powder remains at the
bottom of the container. In this way, the
components are seperated successfully.
4. Seperation by Filtering
• If a heterogenous mixture comprises solid and liquid
components with different densities, than a further
precipitation process is applied in order to seperate
these components. This process is also called
sedimentation.
• After the solid component is precipitated completely,
the liquid component is transferred into another
container. This process is called as decantation.
• Unless there is a great difference between the densities
of solid and liquid components and the solid
components has large-diameter particles, the
decantation process becomes difficult. In this case,
filtering process is applied.
For example; When the
soil and water are mixed up
thoroughly, the water is
filtered through the filter
paper and the insoluble soil
particles remain over the filter
paper. So the muddy water has
been seperated into its Figure 1.3. Seperation of the
components (Figure 1.3).
muddy water by filtering
In filtration method, several filters with different pore
sizes can be used. In order to perform the filtration
process thoroughly, a filter paper with a smaller pore
size than the diameter of the solid particles must be
selected.
5. Centrifuging:
If the solid particles in the liquid are very small
and there is no great difference between the
densities of the solid and liquid components,
filtration can not be sufficient to seperate these
components.
The instruments called centrifuges are used to
precipitate the solid particles. This process is also
applied in the other regular seperations and is
time saving.
6. Seperation Funnel:
To seperate two liquid components with different densities and
showing nonsoluble characteristics within eachother a funnel can be
used. To illustrate; Olive oil-water mixture has been poured into the
funnel.
The olive oil is collected at the
top of the funnel, while the
water that has a greater density
than olive oil is collected at the
bottom of the funnel. (Figure
1.4). After waiting for a while,
the tap is turned on and the
water is poured into another
container. With this way the
liquids have been seperated.
Figure 1.4. Seperation of two liquids
with different densities by a funnel
7. Seperation by the difference in solubility
Since the solubility is a distinguishable property for
the matter, mixtures can be seperated easily by using this
principle
Figure 1.5. Seperation of salt and sand components by the
difference in solubility
• E.g; sand and salt are mixed up in the
water. Salt is soluble in water, whereas the
sand particles precipitate because they are
not dissolved in water. The solution is
seperated by dissolving from sand. When
salty water is evaporated, the rest
remaining from the evaporation is just
salt. As a result, salt and sand are
seperated.
• This method is only applicable when one
of the components is able to be dissolved
in the solvent and the other component is
not.
B) Seperation Techniques of Homogenous Mixtures
1. Distillation
Every substance has a different boiling point.The process
of changing the state of a component into gas phase and
condensating it to recover each component seperately by
making use of this property is identified as distillation
The liquid in the distillation flask is evaporated . Further,
the vapor is passed through the cooler and the vapor
condensate is accumulated in the collector. The liquid
obtained by this way is defined as distillate. So, a solid
component and and a volatile liquid component are
seperated. (Figure 1.6).
Distillation has been classified according to the nature of the
matter in two ways:
a) There are two methods for the seperation of the substances
which have very high boiling points and are not exposed to
degradation :
Simple distillation: It is applicable if there are two
components with very different boiling points. The two liquid
components are heated up. Both of them are vaporized. The
liquid with a lower boiling point exists in the vapor with
considerably greater amounts. This vapor mixture is then
condensed in the reflux cooler. As a result, the liquid in the
collector contains a little of the liquid with a higher boiling
point as impurities. Hence, simple distillation is not a
convenient method for obtaining two components in a
mixture purely. By making a second simple distillation, the
purer form of the liquid with lower boiling point can be
achieved
Figure 1.6 Seperation by Distillation
Fractional distillation: To seperate two liquids which have very
close boiling points to each other, an engaged fractional colomn is
used in additon to the simple distillation mechanism. This colomn
is filled up with the glass particles which do not interact with the
liquids. The rising vapor is gradually condensed over these glass
particles. While the liquid flowing downward, it is heated up again
with the rising vapor and some part of the liquid is vaporized and
goes upward. This vapor contains greater amount of the vapor
from the liquid with lower boiling point, compared to the amount
of vapor at the beginning of the distillation.
When the vapor reaches to the end of the column as described
above, it does not contain any vapor of the liquid with high boiling
point and is collected in the reflux cooler as pure liquid by getting
condensed. This process is defined as Fractional Distillation(Figure
1.7).
Figure 1.7 Fractional Distillation
b) Two different distillation methods are used to seperate
two liquids which have very high boiling points and
degradate before reaching the boiling point :
- Vacuum distillation: The ordinary distillation
mechanism is closed and a vacuum pump has been
engaged into the mechanism. Thus, the components
building up the mixture start to boil at lower boiling
points.
- Water vapor distillation: This system performs the
distillation at 100oC. It is used for the separation of
some volatile vegetable oils which do not get mixed
with water(e.g production of lemon essence)
2) Condensation.
In order to seperate the components of gasgas mixtures, the property of different
condensation points of gases is used. For
example; Nitrogen and oxygene are
obtained, from liquid air since they have
different condensation points.
3) Extraction
If one of the solutes in a solution is dissolved in another solvent
more efficiently and this solvent does not mix with the solvent of
the solution , the second solvent is added into the solution. After
the addition of the second solvent a second phase has been
observed. This mixture is poured into a funnel and shaken
strongly.
During the process the matter in the solution has been carried
into the second solvent which has a better solving ability. This
process is called Extraction.
After the phase seperation has been completed, the second
solvent is seperated through the funnel and after the evaporation
of the solvent the matter is obtained purely. E.g ; Some organic
compounds and metal complexes dissolved in water can be
recovered by means of chloroform which is a better solvent for
these substances than water.
4) Crystallization
The solubility in water of the solid
components building up a mixture vary
according to the temperature. By making use of
this property the solids can be seperated.
Mixtures can be seperated into their
components through the differences in
solubility.
4) Crystallization
Figure1.7. Seperation by the
difference in solubility
A saturated solution at high
temperature of a solid whose
solubility
varies
with
the
temperature is prepared and
allowed to cool down. After a
while, the solid precipitates
(Figure 1.7.). The substances
whose solubility falls with the
decrease in temperature, are
accumulated
as
ordinarily
geometric shaped solids.This event
is named as crystallisation, the
solid particles which have a
certain geometrical form are called
crystals
DECOMPOSITION OF THE
COMPOUNDS
In the previous chapters we learnt how
mixtures can be seperated into their
components by using physical methods. Now,
we are going to analyse how the compounds
are decomposed into the substances
The substances used in casual life and in the
industry, are obtained by the chemical
decomposition of the compounds. To achieve
this, some chemical methods described below
are used.
a. Decomposition by Heat Energy
Some substances are decomposed by the
exposition to heat. For example; When
Mercuryoxide is heated , two different substances
namely Mercury and Oxygene are produced.
Mercuryoxide (HgO) → Mercury (Hg) + 1/2 O2(g)
By means of heat energy two different elements or
two different compounds can be produced from a
single compound. This method is applied very often
in the industry
Mercury (Hg) + O2 → Mercuryoxide (HgO)
HEAT
Mercuryoxide is a compound. When
heated,
It is decomposed into the substances
Mercury
and Oxygene
b. Decomposition by electrical energy (Electrolysis)
Some substances which can not be decomposed by heat energy can
be decomposed into pure substances through electrical energy.
What is electrolysis?
Decomposition of a substance through the passage of electric current
is called electrolysis. The solution which is conducting electricity during
electrolyse is defined as electrolyte. The metal rod or plate which is
dipped into the electrolyte is defined as electrode
For example; Water can be converted into
Oxygene and Hydrogene gases through
electrolyse. A large beaker is filled up with
water. Then, 2 experiment tubes held by the
supporting rods are immerged upside down into
the water.(Air pass into the tubes must be
avoided).
Later, the steel electrodes are connected into
the power supply and installed in the tubes.
After the power supply is adjusted to 9 V and
when the electric current starts to pass through
the tubes, there will be no observable changes
in the tubes.
After the electric current has been cut off and
sulfuric acid is poured into the water and the current
is allowed to pass through the tubes again, gas flow
is observed in both tubes. H2 gas comes out of the
tube connected to the cathode(- ) ,O2 gas comes out
of the tube connected to the anode(+).
Addition of Sulfuricacid(H2SO4) helps the
water to conduct the electric current.
During the electrolysis the gas flows and the events
are described as follows:
H+ ions go to cathode and are reduced in the cathode.
4H+ (aq) + 4 e-  2H2(g)
Oxygen atom in water is oxidated in the anode
2 H2O  4H+ (aq) + O2(g) +4 eNet reaction : 2 H2O  2H2(g) + O2(g)
• Do the oxygene and hydrogen gases have the
same amount of volume after the electrolysis?
• No, they have different volumes. Since , in the
electrolysis proces the volume ratio of the
hydrogen to oxygen is 2/1.
EXAMPLE
After the electrolysis, it is determined that 30 cm3
gas is
collected in the cathode. What will be the amount of volume of
which gas collected in the anode?
Solution
Hydrogen is collected in the cathode, oxygen is produced in the
anode
2 cm3 hydrogen
produced
30 cm3 hydrogen
1 cm3 oxygen is
and
and
X
____________________________________________________
X = (30x1)/2 = 30/2= 15 cm3 oxygen gas is produced
Electrolysis
The electrolysis method is often feasible in
the industry to obtain a lot of substances
purely.
E.g: NaCl(aq)  NaOH + Cl2(g). When the
product NaOH is exposed to electrolysis, Na
metal is produced. Besides metals such as
copper, nickel, gold are obtained in a pure
form by the electrolysis.
c. Other Seperation Techniques
Convertion of some pure substances to other pure
substances can be performed by other methods
except heat and electrical energy.
In nature, metals are abundant in form of oxides. In
order to obtain metals in their purest form, the
metaloxides are put into reaction with the carbon.
E.g; Iron (III) oxide reacts in the high temperature
ovens with the carbon(coke) and iron is produced.
2 Fe2O3 (s) + 3 C(s)  4 Fe (s) + 3 CO2 (g)
c. Other Seperation Techniques
Another way of producing purer metals from
metaloxides is reacting metal solutions with another
metal which is more active.
E.g;When Zink is immerged into the Copper(II)
sulfate solution , it is observed that the Zink rod is
coated with copper and the color of the solution is
changed. Meanwhile the copper is produced in its
pure form.
CuSO4 (aq) + Zn (s)  Cu (s) + ZnSO4 (aq)