Classification of Solutions

Solutions can be classified according to:

1. Polarity of the solute and the solvent
2. Electrolyte and nonelectrolyte solute
3. Particles size of the solute
4. Maximum solubility of the solute
5. Osmotic pressure
6. Polarity of the solute and the solvent

Both of the solute and solvent should have the same polarity to mix and form a homogenous mixture.

In the tables below, two solvents with different polarities are used; namely cyclohexane as none polar solvent and water as a polar solvent. The solubility of these solvents are tested with different solutes: sugar, potassium permanganate and sodium nitrate as polar solutes and oil and iodine as none polar solutes.

One can predict a solution formation if the polarities of the solute and solvent are the same.

This principle is known as: “Like Dissolves Like”

A You Tube illustrate the principle of Like Dissolves Like:

One therefore can distinguish between polar solution from none polar solution.

Solvent	Solute	Solution is Formed?	Reason
Water	Sodium nitrate	Yes	Both solute and solvent have same polarities
Water	Potassium permanganate	Yes	Both solute and solvent have same polarities
Water	Sugar	Yes	Both solute and solvent have same polarities
Water	Iodine	No	Both solute and solvent have different polarities
Water	Oil	No	Both solute and solvent have different polarities

Solvent	Solute	Solution is Formed?	Reason
Cyclohexane	Sodium nitrate	No	Both solute and solvent have different polarities
Cyclohexane	Potassium permanganate	No	Both solute and solvent have different polarities
Cyclohexane	Sugar	No	Both solute and solvent have different polarities
Cyclohexane	Iodine	Yes	Both solute and solvent have same polarities
Cyclohexane	Oil	Yes	Both solute and solvent have same polarities

Molecular Workbench activity illustrates the distribution of large fatty acids molecules with polar part is attracted and soluble in water and none polar part is attracted and soluble in oil.

http://mw.concord.org/nextgen/#interactives/chemistry/solubility/polar-nonpolar-interface-chemistry

Molecule movement in a mixture of oil and water.

Observe how molecules with hydrophilic molecules (which likes to be dissolved in water: polar) and hydrophobic molecules (which dislike to be dissolved in water: nonpolar) are moving between the two regions of the mixture of oil and water, and pay attention to changes in potential energy over time. Move and rotate the molecules to see how they interact with their surrounding environment.

Questions:

1. Explain the alignments of the fatty acids polar part in water with the corresponding potential energy.
2. Explain the alignments of the fatty acids none polar part in oil with the corresponding potential energy.
3. When the fatty acid molecules are rotated, do the polar part and none polar part exchange their regions (i.e. oil region versus water oil)? Why and why not? Explain.

Molecule polarity is illustrated in a Phet simulation activity below:https://phet.colorado.edu/sims/html/molecule-polarity/latest/molecule-polarity_en.html

In the simulation above, the students can explore:

Predict how changing electronegativity will affect the bond polarity.

Explain the relationship between the bond dipoles and the molecular dipole.

Determine if a non-polar molecule can contain polar bonds.

Describe how the ABC bond angle effects the molecular dipole.

Compare the behavior of non-polar and polar molecules in an external electric field.

Two Atoms Screen

Change the electronegativity of the atoms, view the resulting electrostatic potential or electron density, and predict the bond polarity.

Three Atoms Screen

Explore the relationship between the bond dipoles and the molecular dipole, and observe the molecule in an electric field.

Simulation conclusions:

The electronegativity slider ranges from 2 to 4, but the value is never displayed. The resulting electronegativity difference between two bonded atoms varies from 0 to 2.

Bond dipoles are parallel to the bond axis, and their length is linearly proportional to the difference in electronegativity. Note that this is a simplification; in reality, the dipole is not influenced solely by electronegativity.

The molecular dipole is the vector sum of the bond dipoles. In the Two Atoms screen, the molecular dipole is not shown, as it is equivalent to the bond dipole. In the Three Atoms screen, manipulating electronegativity results in an understanding of summing vector magnitudes, while manipulating bond angles results in an understanding of summing vector angles.

The magnitude of an atom’s partial charge is linearly proportional to the electronegativity difference between the bonded pair. If an atom has a higher electronegativity than the atom at the other end of the bond, then the partial charge’s sign is negative; otherwise it is positive. For atoms that participate in more than one bond (e.g., atom B in the “Three Atoms” screen), net partial charge is the sum of the partial charges contributed by each bond.

The electrostatic potential and electron density are linearly proportional to the electronegativity difference set by the sliders. These surfaces are not implemented for the triatomic molecule in the Three Atoms screen, because the manipulation of bond angles results in undefinable surfaces.

The Three Atoms screen allows for students to change the bond angle between the outer atoms C). The    AB and BC bonds are treated independently, and the model does not allow for these atoms to    repel     each other. To explore how atoms would repel one another when the bond angles are changed.

Questions:

1.       Explain how the polarity of a molecule is related to the electronegativity of the atoms within the molecule. Use your knowledge gained from the previous chapters.

2.       Explain how is the solubility of a solution is affected with the polarity and electronegativity

2. Electrolyte and nonelectrolyte solute

Solutes that are soluble in water and can dissociate in water and produce ions are called electrolytes such as sodium chloride (kitchen salt). Electrolytes can conduct electricity because they can produce ions when dissolved in water. Solutes are soluble in water and cannot dissociate in water and cannot produce ions are called nonelectrolytes such as sugar. Nonelectrolytes cannot produce ions and hence cannot conduct electricity.

Electrolytes can be divided into weak electrolytes and strong electrolytes.

Weak electrolytes are solutes that dissolved and dissociate partially in water and conduct electricity to limited extent while strong electrolytes dissociate completely in water and conduct electricity to greater extent.

The table below illustrates the different types of electrolytes.

Electrolyte Type	Dissociation in water	Ions are formed?	Examples	Electricity Conduction
Weak Electrolytes	partially	limited number of ions +large amount of undissociated molecules	weak acids and bases and all metal ions other than group 1A and 2A.HF, HNO2, H3PO4Al(OH)3, Fe(OH)2	partial, weak conduction
Strong Electrolytes	completely	only ions	strong acids and bases and groups 1A and 2A metal ions are forming strong electrolytes:HCl, HNO3, HBr, H2SO4NaOH, KOH,Mg(OH)2	complete, strong conduction
None Electrolytes	No	No	Sugar C6H12O6Ethanol C2H5OHHoney	No

A You Tube explains how to identify electrolytes (weak and strong) and nonelectrolytes:

3. Particles size of the solute

According to the particles size of the solutes, one can differentiate between three types of mixtures: homogeneous mixture (normal solution), heterogeneous mixture (colloid) and another heterogeneous mixture called suspension.

Normal solutions have solutes with smaller particles size and the particles not be seen by the naked eyes or any other optical tools such as microscopes. The size of particles is below 1.00 nm (nano meter) and the particles cannot be seen by naked eyes. Normal solutions are considered as homogenous mixtures.

Colloids have solutes with larger particles size. The size of particles is between 1.00 nm – 100.0 nm and therefore the particles can be seen by optical tools such as microscopes but not by naked eyes. The particles can be seen by a Tyndall Effect by which a colloidal solution is exposed to a light source. The light is scattered and reflected due to the particles size of the solutes and the particles of solute can be exposed and seen then by naked eyes. Colloids are considered as heterogeneous mixtures.

Furthermore, colloidal solutions are not stable and cannot pass through membranes or semi membranes.

The suspensions have solutes with the largest particles sizes. The size of particles is great than 100.0 nm and therefore they can be seen by naked eyes. Suspensions tend to settle out

A YouTube video illustrate the difference between the three solutions

The table below can summarize the differences between solutions, colloids and suspensions

	Mixtures Appearance	Particles size	Tyndall Effect	Settling Out	Semi Membranes Separation	Examples
Solutions	transparent	Less than 1.00 nm	No	No	No	Sugar dissolved in water
Colloids	Cloudy, homogeneous	1.00 nm – 100.0 nm	Yes	No	No	Foam, Smoke, Clouds
Suspensions	Cloudy, heterogeneous	Greater than 100.0 nm	No, if particles settle out	Yes	Yes	Char Coal suspension in water

4. Maximum solubility of the solute

There are three types of solutions according the maximum solubility of the solute in the solvent:

1. Unsaturated solution

The solute amount in the solution is less than the maximum amount. An example of unsaturated solution is sodium chloride in water. Maximum solubility of sodium chloride in water at room temperature of 25 ^O C is 357 mg/mL. If sodium chloride amount is less than 357 mg/mL (less the maximum solubility of solute in solution), then the solution is considered to be unsaturated solution and it is homogeneous. Most of the solutions used in the chemistry laboratory are unsaturated. They tend to be very stable and very often are called stock solutions.

2. Saturated solution

The solute amount in the solution is equal to the maximum solubility of 357 mg/mL at room temperature. The solution is still homogeneous mixture and tend to be more viscos. Any addition of the solute after the saturation point is reached will lead to the extra incoming solute particles to settle out of the solution.

3. Supersaturated solution

The amount of the solute is large and it exceeds the maximum solubility amount of 357 mg/mL at room temperature. The solution tends to be heterogeneous and the solute particles tend to settle out.

A You Tube illustration can be seen below:

The table below summarizes the three types of solutions

Solution	Amount of Solute	Appearance of the Solution	Mixture type
Unsaturated	Less than the maximum solubility of solution in solvent	Transparent	homogenous
Saturated	Equal the maximum solubility of solution in solvent	Thick, viscos	homogenous
Supersaturated	Very large, exceeds the maximum solubility of solution in solvent	Particles settle out	heterogeneous

Maximum Solubility calculations:

Example:

The maximum solubility of NaCl is 35.7 grams in 100.0 gram water at room temperature of 25 ^oC. If there is a solution made of 95.0 grams of NaCl in 200.0 grams water at room temperature 25 ^oC. Answer the following questions:

1. How many grams of NaCl will be dissolved
2. How many grams of NaCl will not be dissolved and remain in solution
3. Is this solution is saturated or supersaturated?

1. How many grams of NaCl will be dissolved?

Grams of NaCl = [200.0 g H₂O] x [35.7 g NaCl / 100.0 g H₂O] = 71.4 g NaCl

1. How many grams of NaCl will not be dissolved and remain in solution

Undissolved NaCl = 95.0 g NaCl – 71.4 g NaCl =23.6 g NaCl remaining

1. If 95.0 g NaCl is added to 200 grams at room temperature, 23.6 g NaCl will not dissolve and settle out at the bottom of the mixing container. The solution then is said to be supersaturated.

Osmotic pressure

Osmosis is the diffusion of a solvent such water with higher amount (less amount of solute) through a semi membrane into a solution with higher solute concentration and less solvent amount.

A You Tube video illustrates the osmosis concept.https://www.youtube.com/embed/-g-VJymtAf4?feature=oembed

The solution is classified as isotonic, hypotonic and hypertonic according to the amount of the solvent outside and inside a cell. Red A blood cell has the concentration of glucose about 5% and sodium chloride amount 0.9% and rest is water

The table below exhibits the details difference between these three tonic solutions

Solution	Glucose 5%	Sodium Chloride 0.9% inside cell	Water inside cell	Sodium Chloride 0.9% outside cell	Water outside cell	Status of cell
Isotonic	No change	0.9%	No Change	0.9%	No change	Healthy, normal red cells sizes
Hypotonic	No change	Higher than 0.9%	Lower amount	Less than 0.9%	Higher amount	Hemolysis, red cells are swollen
Hypertonic	No change	Lower than 0.9%	Higher amount	Higher than 0.9%	Lower amount	Crenation, red cells are shrunk

A You Tube video illustrates the different types of tonicity of the solutions according to its osmosis.https://www.youtube.com/embed/BGtLQSfFQsA?feature=oembed