Solutions

Key Terms

Suspension

Colloid

Emulsion

Solution

Solute

Solvent

Alloy

Any sample of matter is either a pure substance or a mixture of pure substances

Heterogeneous Mixtures

The amount of each substance in different samples of a heterogeneous mixture varies

Particles in a suspension are larger and eventually settle out

Suspension is a mixture in which particles of a material are more or less evenly dispersed throughout a liquid or gas.

Particles in a suspension may be filter out.

Particles in suspensions are usually the size of or larger than the tip of an extremely sharp pencil.

Particles of this size are large enough that they can be filtered out of the mixture.

You can classify a mixture as a suspension if the particles settle out or can be filtered out.

Some mixtures of two liquids will separate.

The two liquids separate because they are immiscible. Meaning they do not mix.

In order to separate two immiscible liquids we can pour the less dense liquid of the top by a process called decanting .

Particles in a colloid are too small to settle out

Colloid is a mixture consisting of tiny particles that are intermediate in size between those in solution and those in suspension and that are suspended in a liquid, solid, or gas.

What is the Tyndall effect?

It is the scattering of light though a colloid mixture

Other familiar materials are also colloids

The particles in most colloids are composed of many atoms, ions, or molecules, but individual protein molecules are also large enough to form colloids.

Some immiscible liquids can form colloids

Mayonnaise is a colloid consisting of very small droplets of oil suspended in vinegar.

Mayonnaise is an emulsion

An emulsion is a colloid in which liquids that normally do not mix are spread throughout each other.

Like other colloids, an emulsion has particles so small that it may appear to be uniform.

Homogeneous Mixtures

Homogeneous mixtures not only look uniform but are uniform.

Homogeneous mixtures are solutions

Solutions are homogeneous mixtures of two or more substances uniformly dispersed throughout a single phase.

Solute in a solution, the substance that dissolves in the solvent

Solvent in a solution, the substance in which the solute dissolves

Mixtures are homogeneous when the smallest particles of one substance are uniformly spread among similar particles of another substance.

All homogeneous mixtures are also solutions

Miscible liquids mix to form solutions

Two or more liquids that form a single layer when mixed are said to be miscible

How can we separate miscible liquids?

By a process call distillation. Distillation works only when the two miscible liquids have different boiling points.

Liquid solutions sometimes contain no water

What are some examples of liquid solutions that do not contain water?

1. Nail-polish remover2. paint strippers3. gasoline

Other states of matter can also form solutions

Solutes and solvents can be in any state.

Solids can dissolve in other solidsAlloy is a solid or liquid mixture of two or more

metals.

The mixing of solids is when they are in a liquid state then turned back into a solid.

Alloys are important because they have properties that the individual metals do not have.

Not all alloys contain metals. Some types of steel are alloys containing the nonmetal element carbon

1. a. homogeneous b. homogeneous c. heterogeneous d. heterogeneous

2. Particles in a suspension are larger than those in a colloid. As a result, the particles in a suspension settle out and can be filtered out, but those in a colloid do not settle out an cannot be filtered out.

3. Air, Mixtures of gases, dental amalgam, sterling silver, brass, bronze, and other metal alloys

4. Water is the solvent and baking soda or sodium hydrogen carbonate is the solute.

5. Sugar water, egg white, muddy water6. Distillation can separate liquids that have different boiling

points. The boiling points of formic acid and water are too close together for separation by distillation.

7. Show her that the drink is sweet which is evidence that the sugar is still present. Allow the water to evaporate, showing that the crystalline sugar is regained, although contaminated with the drinking flavoring.

Key Terms

Polar Compound

Hydrogen Bonding

Nonpolar Compound

Water: A Common Solvent

Two-thirds of Earth’s surface is water and three-fourths of your body weight is water. Many different substances can dissolve in water. For this reason water is sometimes called the universal solvent.

Water can dissolve ionic compounds because of its structure

Polar Compound is a molecule that has an uneven distribution of electrons.

A polar molecule has a distinct positively and negatively charged side. Water molecules attract both the positive and negative ions of an ionic compound.

Polar water molecules pull ionic crystals apart.

Dissolving depends on forces between particles

To dissolve an ionic substance, water molecules must exert a force on the ions that is more attractive than the force between the ions in the crystal. This is true for all solvents

Water dissolves many molecular compounds

Water has a low molecular mass, but it is a fairly dense liquid with a high boiling point. Water has these properties because of hydrogen bonding.

Besides ionic compounds, water also dissolves many molecular compounds, such as ethanol, ascorbic acid, and table sugar.

Like dissolves like

A rule of thumb in chemistry is that like dissolves like. For example, water is a polar molecule because it has positive and negative ends. So, water dissolves ions and polar molecules, which also have charges.

Nonpolar Compounds are compounds whose electrons are equally distributed among its atoms. Usually will not dissolve in water.

The Dissolving Process

Remember that molecules are always moving (Kinetic theory of Matter). Since the molecules are always moving they are colliding with each other and other objects. As the molecules of a solvent collide with a solute the solute begins to dissolve.

Solutes with a larger surface area dissolve faster

Stirring or shaking a solution helps the solute dissolve faster

Solutes dissolve faster when the solvent is hot

Solutes affect the physical properties of a solution

By adding sodium chloride to water you can increase the boiling point and also lower the freezing point

1. Water is a polar molecule, which means that one end has slight positive charge and the other end has a slight negative charge. These charged ends are attracted to opposite charges on the other polar molecules, such as methanol and to charged ions in ionic substances, such as ammonium chloride. As a result water molecules can pull polar molecules and ions into solution.

2. Solvents can dissolve a substance only if the attraction of the solvent molecules for the particles of the substance is greater than the attraction between the particles of the substance.

3. The larger crystals of salt have less surface area exposed to water than the same mass of smaller crystals. Therefore, more sodium and chloride ions are attracted by water molecules at the surface of the smaller crystals.

4. Water will dissolve glycerol because the polar water molecules attract the polar groups of glycerol and pull it into solution.

5. Raising the temperature of the water, shaking, or stirring the mixture would increase the rate of dissolving of the salt.

6. The presence of a solute lowers the freezing point of a solution below that of the pure solvent. So, the freezing point of the drink mix is lower than that of water, and the drink mix has not become cold enough to freeze, although that water has.

Key Terms

Solubility

Concentration

Unsaturated Solution

Saturated Solution

Supersaturated Solution

Molarity

Remember that not all substances dissolve in water. If a substance does not dissolve it is said to be insoluble.

Solubility in Water

As you know substance are not soluble in water. However, substance that are soluble in water have a limit to how much of the substance will dissolve in water. The maximum amount of substance that will dissolve in water is called solubility.

Solubility is the maximum amount of a solute that will dissolve in a given quantity of solvent at a given temperature and pressure.

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Example:

The maximum amount of salt that can be dissolved in 100g of water at room temperature is 36g.

There are some substances that are completely soluble in water. This means no matter how much you add it will all mix with water to form a solution.

Some ionic compounds, such as silver chloride (AgCl), are almost completely insoluble in water.

Different substances have different solubilities (Table 1 pg 240).

Even closely related compounds can have very different solubility. The solubility of a compound depends on the forces acting between water molecules and solute particles compared to the forces acting between the solute particles

Concentration is the quantity of solute dissolved in a given volume of solution. If the solution contains a large amount of solute it is concentrated. If there is only a small amount it is dilute.

Unsaturated solutions can dissolve more solute

An unsaturated solution is a solution that contains less solution than a saturated solution does and that is able to dissolve more solute.

At some point, most solution become saturated with solutes

Once a solution becomes saturated with solutes it is no longer able to dissolve the solute.

Saturated solutions cannot dissolve any more solute under the given conditions

Heating a solution usually dissolves more solutesaturated

So by changing the given conditions, we are able to dissolve more solute into a solution. This cause the solution to become a supersaturated solution.

A supersaturated solution is a solution that is holding more dissolved solute than is required to reach equilibrium at a given temperature.

What happens to the solute when the temperature decreases?

The solute will remain in solution until something is added to cause the solute to dropout. The solute will continue to fall out until the solution is saturated at the cooler temperature.

Temperature and pressure affect the solubility of gases

Concentration of Solutions

Describing a solution as concentrated, dilute, saturated, or unsaturated still does not reveal the quantity of dissolved solute.

http://www.radiochemistry.org/periodictable/index.shtml

1. Some substances are only slightly soluble in water. For example, only 0.32g of calcium sulfate dissolves in 100g of water. Such a solution is saturated because it contains the maximum amount of solute, but still dilute because it contains only a little solute per unit volume.

2. The solution can be heated and additional solute dissolved. When the solution is cooled to the original temperature, it will be supersaturated.

3. By adding small amounts of salts we can determine if the saltwater is unsaturated, saturated, or supersaturated. If it dissolves, the solution is unsaturated. If it remains undissolved, the solution saturated. If new crystals form in the solution, the solution is supersaturated.

4. Acetic acid is completely soluble in water, while olive oil is completely insoluble in water. The solubility of olive oil is zero, and the solubility of acetic acid is effectively infinite.

5. Evaporation would take place faster at 37% humidity because the solution of water vapor in air is less saturated than it is at 92% humidity.

6. 0.5 M7. Gases such as nitrogen and oxygen, from the air are

dissolved in the cold water. Gas solubility decreases with increasing temperature, so the dissolved gas has come out of solution, forming bubbles as the temperature of the tap water increases.