Transcript 3Solutions 1011

Solutions
Mathematicians
have Problems,
But Chemists
have Solutions!
Ionic Solvation
Covalent Solvation
Objectives
 To
compare and contrast solute and
solvents
 To determine if a molecule is ionic, polar
covalent, non-polar covalent, or metallic
 To describe how a non-polar solute will
dissolve in a non-polar solvent.
What is a solution?

A solution is a mixture of 2 things,
the solute and the solvent.

solute
solution
Another word for a solution is a
homogenous mixture. A homogenous
mixture is when 2 or more things are
mixed, but you only see one thing.

A solute is what dissolves or
disappears, like salt or sugar.
 A solvent is what does the
dissolving. It is what you see when
you look at a solution. Water is
called the universal solvent.
 You will always have more
solvent than solute.
 Solvation is the scientific way of
saying “dissolving.”
solvent
Solvation Examples
 Example:


Salt
What is the solute?___________
water
What is the solvent?___________
 Example



Salt water
– 70% ethanol solution.
Water
Solute _______________
ethanol
Solvent________________
Why? If 70% is ethanol, then it must be the solvent.
The remaining 30% is water, the solute.
Studying Solvation

We want to predict what
solutes will dissolve in Heterogeneous
which solvents.
Mixture:
 In order to do this, we
need to know what type Different Bond
Types
of molecule the solute
and solvent are.
 The type of molecule and
the IMFs that form will
help us to determine if
solvation will occur.


Like molecules will hang
out with each other to
form a solution
Molecules that are not
alike will separate from
each other.
Solvent:
H2O (polar)
Homogeneous
Mixture:
Same Bond
Types
Solvent:
H2O
(polar)
Solute: any
non-polar
Solute:
any polar
or ionic
Bond Review

How can you tell if a molecule is
ionic, polar covalent, non-polar
covalent, or metallic?
 Ionic:





Electronegativity difference of 1.8 or
more
1st element in groups 1-3, metals, 2nd
element is in groups 5-7 non-metals
strongest IMF
Metallic: two metals combining
electrons
Covalent:
1.
2.
Polar has un-bonded pair of e- on
central element (usually grps 5 or 6)
or
Polar will have 2 different elements
bonded to central element (usually
groups 3 or 4)
Solvent: Water
molecules
Solute: Na+ or Cl-
Determine what type of bond hold
the molecule together
 KCl
Ionic
 H2O
Polar covalent
 CaCO3
Ionic (polyatomic)
 CO2
Non-polar covalent
 Sugar
Polar covalent: memorize
 Benzene
Non-polar covalent
Water
 Water

H
H
is a polar molecule. Why?
O
Because oxygen has 2 unbonded pairs
 This
means the oxygen is negatively
charged and both hydrogens are positively
charged. Why?

Because oxygen hogs the e-
 What

type of IMFs will water have?
Polar molecules can have dipole-dipole or
hydrogen bonds. Water has both H & O, so
molecules are held together by hydrogen
bonding, the strongest IMF.
Ionic Solubility Rules
We can predict if a solute will dissolve in a solvent
by using looking at the bonds of each molecule.
“Like Dissolves Like”
 Ionic
or Polar solutes will dissolve in
ionic or polar solvents
 Alcohols (ending in –ol or OH) will
dissolve anything BUT polar covalent
solids.

Ethanol, methanol, isopopanol are alcohols
and will dissolve anything except polar
covalent solids like sugar.
 Water
is considered a universal solvent
because it can dissolve both ionic and
polar covalent compounds
Ionic Compounds & Water

In an aqueous solution, water is the solvent.
HCl (aq), NaCl(aq), CuSO4 (aq)
 Ionic solutes will dissociate into its ions when
dissolved in water. Why?

Because the charged parts of ionic bonds
are heavily attracted to the charged parts of
water.
 NaCl (in water)  Na+ + Cl
K2SO4 (in water )
2K+ + SO42-
Ionic Solvation: NaCl & H2O
1. Salt solute is added to water.
2. Salt randomly moves around until it bumps into or “hits
on” the water molecules.
The Na+ part of the salt is very attracted to the bad boy
Oxygen and his negative charge.
The Cl- part of the salt is very attracted to the good little
girl Hydrogen and her positive charge
3. Salt dissociates or breaks up into Na+ and Cl-.
4. Each ion is completely surrounded by water molecules
“groupies!”.
When the ion can no longer be seen, it is said to be
dissolved.
Ionic Solvation
Cl
Na
+
H
H O
+
+
Na+
+
Cl+
H
+
H O
Solvation Animation
Ionic Solvation Animation #1
Ionic Solvation Animation
Polar Covalent Solvation: Sugar
Water
1. Sugar is added to water.
2. Sugar will randomly move around until it bumps into the
water molecules
3. The partially charged part of sugar is very attracted to
part of the oppositely charged part of water.
4. The covalent solute (the sugar) DOES NOT break up.
5. Instead, the sugar becomes a cheater by staying
bonded and forming a partial relationship with the water.
6. When the sugar is completely surrounded by solute
“groupies,” we say it has been dissolved.
Ions that are completely surrounded by water molecules
form hydration spheres and are said to be “hydrated”.
Polar Solvation

Polar molecules will
dissolve in water
because of the
attractions of the
charges
 The charged parts of
the sugar are attracted
to partial charged areas
of water
 Water surrounds the
sugar
Solubility Rules

We can predict if a solute will dissolve in a
solvent by using looking at the bonds of each
moelcule.
“Like Dissolves Like”
 Ionic
or Polar substances will dissolve in
ionic or polar solvents
 Non-polar substances will only dissolve in
non-polar substances.
 Alcohols (ending in –ol or OH) will
dissolve anything BUT polar solids.
 Water is considered a universal solvent
because it can dissolve both ionic and
polar covalent compounds
Like Dissolves Like
You must first identify if the molecule is
ionic, polar, or non-polar.
Will NaCl dissolve in water?
Ionic Solid +
Polar solvent =
Will CO2 dissolve in water?
Non-polar +
Polar solvent =
Solution YES!
No solution NO!
Will oil dissolve in vinegar?
Ionic Solid +
Polar solvent =
Solution YES!
Will sugar dissolve in water?
Polar Solid +
Polar solvent =
Solution YES!
Solvation Stories
What happens when molecules face
temptation!
AKA: Celebrity Marriage… TMZ Style
Objectives
 When
given a solute, determine if it is ionic
polar covalent, or non-polar covalent
 To describe what happens to an ionic
solute when it dissolves in a solvent
 To describe what happens to a polar
covalent solute when it dissolves in a
solvent
 To identify 4 ways to increase the solubility
of a solute
 To interpret a solubility curve
Solvation Animation
Ionic Solvation Animation #1
Ionic Solvation Animation
Factors that Affect Solvation
We can speed up the process in a couple of
ways:
1. Shake or stir the mixture
2. Increase the temp (solids or liquids only)
3. Increase the surface area of solute
4. Increase the pressure (gases only)
Why does each of the above work?
Because it will increase the number of
collisions!
Solubility
Curves

Solubility depends on
the molecule and the
temp
 Graph allows us to
predict the solubility
under different temps
 Which one is the only
molecule where solubility
decreases as you
increase temp? Why?
 Because it is a gas.
Solubility Curves
Questions
1.
2.
3.
What is the solubility
of KCl at 70°C? 47 g
How many grams of
KClO3 will dissolve
in 100 grams of
water at 40°C ? 15 g
How many grams of
KClO3 will dissolve
in 50 grams of
water? 15 g KClO3 =
100 g H2O
x
50 g H2O