Download Solution is

Inorganic
and
analytical chemistry
Types of Mixtures
Matter surrounding us is broadly
divided into three phasessolids, liquids and gases.
:
1) Pure Substance
A pure substance can be either an element (just one
type of atom) or a compound.
elements
Mercury
compounds
water
silver
NaCl
Oxygen
sucrose
Mixtures
Most objects around us are mixtures.
– Example: most foods and beverages, air, the chair you
are sitting in.
• The components are physically mixed together and can
be separated by physical methods.
• The properties of mixtures depend on the identity and
amount of each component in the mixture
– Therefore to fully describe a mixture, the composition
of the mixture must be stated.
• Example: 5% Starch solution, 75:25% Zinc/Copper Alloy
•
Mixtures can be either uniform in composition (homogeneous) or the
composition can vary throughout the sample (heterogeneous).
• Homogeneous mixtures = uniform throughout, appears to be one
thing
– Homogenous mixtures are called solutions.
– Solutions can be liquid, gas, or solid
– Examples:
Sugar dissolved in water (liquid)
Air (gas)
14-karat gold (solid mixture of gold, silver, and
copper)
• Heterogeneous
mixtures = non-uniform,
contains regions with different properties
than other regions
– Examples:
chocolate chip cookies
sand in water
Solution is a homogenous mixture of molecules,
atoms , or ions of two, or more different substances
.Generally one of the components is in large quantity
and the others are in small quantities. The large
quantity part of the substance is called the solvent in
which the smaller quantities called solutes are mixed
which is termed as dissolution
Solutions in which water is the solvent are called aqueous
solutions
•
Solubility
is defined as the amount of solute that dissolves in
a given quantity of solvent to form saturated
solution.
The solubility depends on a number of factors:
Kind of solvent, kind of solute, temperature,
pressure and physical state of matter.
Table 1
General Rule
Like dissolves like"
*Polar solvent ( water ) is a good solvent for
ionic compounds (NaCl).
*Gasoline (non polar compounds is a good
solvents for other non polar organic
compounds (oil).
For example, both carbon tetrachloride (CCl4)
and benzene (C6H6) are nonpolar liquids. The
only intermolecular forces present in these
substances are dispersion forces .When these
two liquids are mixed, they readily dissolve in
each other, because the attraction between CCl4
and C6H6 molecules is comparable in magnitude
to the forces between CCl4 molecules and
between C6H6 molecules.
• Electrolytes
Are compounds that dissolve in water to form ions.
– The consequences of having too much or too little of a
particular electrolyte can have profound effects on your
health.
The mode of electrolytic and non-electrolytic solutions has
been used to explain all the physical properties of
solutions(osmosis and dialysis)
– Ions important to your health:
• Na+, K+ = transmission of nerve impulse
• Ca2+ = muscle contraction and blood clotting
Arrhenius Theory of Electrolytes
When ionic compounds are dissolved in water, the ions
released and they distribute themselves uniformly in the
water.
Polar covalent bonds form ions when dissolved in water,
non electrolytes dissolve in water, neutral molecules are
released.
Hydration: is a close association of water molecules with an
ion and the ion said to be hydrate.
According to Arrhenius model, the total number of ions
formed per mole of electrolyte depends on the chemical
formula of the electrolyte. (See table below):-
Number of ions formed per mole of electrolyte
Chemical formula
Ions formed in
aqueous solution
Number of ions in 1
mole off electrolyte
NaCl
Na+ Cl-
2*6.02*1023
KNO3
K+ NO-3
2*6.02*1023
CaCl2
Ca+ Cl- Cl-
3*6.02*1023
Na3PO4
Na+ Na+ Na+ PO4-3
4*6.02*1023
Colloids and Suspensions
In a true solution, the maximum diameter of a solute
particle is about 1 nm.
Colloid: A suspension in solvent in which the solute
particle diameter is between 1 nm and 1000 nm.
Colloid particles have very large surface areas, which
causes colloidal systems to have two properties:
They scatter light (Tyndall Effect) and, therefore,
appear turbid, cloudy, or milky, not transparent.
They form stable dispersions; that is, they do not settle
out.
Colloids are intermediate between homogeneous and
heterogeneous mixtures.
Properties of Colloids
Tyndall effect: a characteristic of colloids in which light
passing through the colloid scatters.
When we see the beam of a flashlight through smoke, dust
or fog we are observing the Tyndall effect.
Brownian motion: the random motion of colloid-size
particles.
An example of Brownian motion is the motion of dust
particles in the air; what we see is not the dust particles
themselves but the flashes of scattered light passing
through the colloid due to the Tyndall effect.
Suspensions scatter light.
Colloids often scatter light
Properties of Colloids
Why do colloidal particles remain in solution despite all
the collisions due to Brownian motion?
In liquids, most colloidal particles are surrounded by a large
solvation layer; if the solvent is water, as in the case of protein
molecules in the blood, the large number of surrounding water
molecules prevents colloidal molecules from touching and
sticking together.
In gases and liquids, because of their large surface area,
colloidal particles acquire static charges; for example,
they all may become negatively charged. When a
charged colloidal particle encounters another particle of
the same charge, they repel each other.
Examples of Colloids: Milk
• Milk appears to be homogeneous. But under a
microscope you see that milk contains globules
of fat and small lumps of the protein casein
dispersed
in a liquid called whey. Milk is colloid because
the particles of casein do not settle out after
standing.
• A suspension contains large particles
suspended in a liquid.
• The particles will eventually, slowly settle to
the bottom in the absence of agitation
Suspensions: Muddy Water
Summary of Solutions, Colloids ,And Suspensions
Diffusion
and
Osmosis
Diffusion and Osmosis
Liquid molecules travel randomly in all directions
and mix quickly with other liquid molecules in a
process called diffusion.
Diffusion is the movement of one substance within
another substance until it is evenly distributed.
Substances move from areas of higher concentration to
those of lower concentration by diffusion.
Certain membranes, called
semipermeable membranes,
are barriers to diffusion because
they allow solvents, but not all
solutes to pass through.
• The semipermeable
membrane in the image allows
water to pass but not the Na+ or
Cl- ions
Although water moves back and forth through most
semipermeable membranes, it flows more forcefully from
the side of the membrane with lesser solute concentration
to the side with greater solute concentration.
The net movement of water across a membrane from a
solution of lesser solute concentration to one of
greater solute concentration is called osmosis.
Osmotic Pressure
Semipermeable membrane: A membrane with tiny pores that are
big enough to allow solvent molecules to pass through them, but
not big enough to allow the passage of large solute molecules.
Example: a cell wall!
Osmosis: the movement of solvent particles through a
semipermeable membrane from a region of lower solute
concentration (higher solvent concentration) to a region of higher
solute concentration (lower solvent concentration).
Osmotic pressure: the pressure necessary to prevent osmosis.
Osmolarity (Osmol): the molarity multiplied by the number of
particles produced by each formula unit of solute.
The pressure associated with the
transport of water in the osmosis
process is called: osmotic pressure.
The greater the difference in solute
concentrations across the semipermeable
membrane, the greater the osmotic pressure
b. As a osmolarity (1 osmole = 1 mole
(Avegadros’s # of particles) in 1 kilogram of
water)
(1) Osmolarity is a reflection of the number of
particles in a solution and not the type of particle
in a solution.
(2) The osmolarity of body fluids is important
because it influences the movement of water in
and out of cells.
*Isotonic
solution: a term used
primarily in the health
sciences to refer to a solution
with the same osmolarity
as blood plasma and red blood
cells.
*Hypertonic
solution: a solution
with higher osmolarity
than red blood cells.
*Hypotonic
solution: a solution
with lower osmolarity
than blood plasma and red blood
cells
*Hemolysis:
the swelling and
bursting of red blood cells
because they cannot resist the
increase in osmotic pressure
when put into a hypotonic
solution.