SOLUTIONS 19.2

Chapter Nineteen: Solutions

19.1 Water

19.2 Solutions

19.3 Acids, Bases, and pH

Chapter 19.2 Learning Goals

Explain how solutions are formed.

Define solubility and interpret solubility graphs.

Describe factors that affect the concentration of solutions.

Compare and contrast solubility of solid, liquid, and gaseous matter.

19.2 Water and solutions

A solution is a mixture of two or more substances that is uniform at the molecular level.

19.2 Water as a mixtureMuddy water not a solution.

Muddy water is heterogeneous because it contains larger particles of soil or plant debris.

19.2 Water and solutions

Although we often think of solutions as mixtures of solids in liquids, solutions exist in every phase; solid, liquid, or gas.

Solutions of two or more solids are called alloys.

Steel is an alloy (solution) of iron and carbon.

19.2 Suspensions

In a mixture called a suspension the particles can range widely in size.

Muddy water, a suspension, will settle when it is left still for a period of time.

19.2 Colloids

Colloids are mixtures, and look like solutions, but their particles are too small to settle to the bottom of their container over time.

Examples of colloids are mayonnaise, egg whites, and gelatin.

19.2 Tyndall effect

Tyndall effect is occurring if you shine a flashlight through a jar of liquid and see the light beam.

19.2 Types of mixtures How can you tell the difference between a solution, a colloid and a suspension?

First, try filtering it, then look for the Tyndall effect.

19.2 Water and solutionsA solution contains at least two components: a solvent, and a solute.

The solvent is the part of a mixture that is present in the greatest amount.

Which of these is the solvent?

19.2 Water and solutionsWhen the solute particles are evenly distributed throughout the solvent, we say that the solute has dissolved.

19.2 SolubilityThe term solubility means the amount of solute (if any) that can be dissolved in a volume of solvent.

Is there a limit for how much seltzer (solute) can dissolve in water (solvent)?

19.2 SolubilityChalk and talc do not have solubility

values.

These substances are insoluble in water because they do not dissolve in water.

19.2 SolubilityA solution is saturated if it contains as much solute as the solvent can dissolve.

Any solute added in excess of the substance’s solubility will not dissolve.

What will happen to any un-dissolved gas when you unscrew the cap of seltzer water?

Solving Problems

Seawater is a solution of water, salt, and other minerals.

How much salt can dissolve in 200 mL of water at 25 °C?

1. Looking for: …grams of solute

2. Given … v = 200 mL; T = 25 C

1. Looking for: …grams of solute

2. Given … v = 200 mL water; T = 25 C

3. Relationships: Solubility table for reference 38 g of salts in 100 mL water at 25 °C

4. Solution …if there are 38 g salt/100 mL water, then “x” g/ 200 mL water = 76 g salts are need in 200 mL of water

Solving Problems

19.2 SolubilityA solution is saturated if it contains as much solute as the solvent can hold.

An examples of a saturated solution is air.

Air can be saturated with water. (We call it humidity!)

19.2 Solubility

For something to dissolve in water, the water molecules need to break the bonds between the solute molecules.

Water dissolves each substance differently because the chemical bond strengths between atoms found in different solutes are not the same.

19.2 Solubility graphsSolubility values for three solutes are

plotted in this temperature-solubility graph.

19.2 ConcentrationIn chemistry, it is important to know the exact concentration of a solution—that is the exact amount of solute dissolved in a given amount of solvent.

19.2 Concentration

Two other common ways of expressing the concentration of a solution are molarity and mass percent.

19.2 Concentration

Molarity is equal to the moles of solute per liter of solution.

19.2 Concentration

The mass percent of a solution is equal to the mass of the solute divided by the total mass of the solution multiplied by 100%.

Solving ProblemsHow many grams of salt (NaCl) do you

need to make 500 grams of a solution with a mass percent of 5% salt? The formula mass of NaCl is 58.4 g/mol.

What is the molarity of this solution?

1. Looking for: …grams of solute

2. Given … mass solvent = 500 g; concentration = 5% …formula mass = 58.4 g/mol

3. Relationships: Mass percent = mass of solute x 100%

total mass of solution Molarity = moles of solution liter of solution

4. Solution … 5% = (mass of salt ÷ 500 g) × 100% …0.05 × 500 g = 25 g # of moles = 25 g = .4 moles

58.4 g/mol Assume 1 L of solution = .4 moles/L = .4M

Solving Problems

19.2 EquilibriumWhen a solute like sugar is mixed with

a solvent like water, two processes are actually going on continuously. Molecules of solute dissolve and go into solution. Molecules of solute come out of solution and

become “un-dissolved.”

When the rate of dissolving equals the rate of coming out of solution, we say equilibrium has been reached.

19.2 EquilibriumWhen a solute like sugar is mixed with

a solvent like water, two processes are actually going on continuously. Molecules of solute dissolve and go into solution. Molecules of solute come out of solution and

become “un-dissolved.”

When the rate of dissolving equals the rate of coming out of solution, we say equilibrium has been reached.

19.2 Equilibrium

When a solution is unsaturated its concentration is lower than the maximum solubility.

A supersaturated solution means there is more dissolved solute than the maximum solubility.

19.2 Solubility of gases in liquids Some solutions have

a gas as the solute.

When you drink carbonated soda, the fizz comes from dissolved carbon dioxide gas (CO2).

19.2 Solubility of gases in liquidsWhen temperature increases,

the solubility of gases in liquid decreases.

19.2 Solubility of gases in liquidsThe variety and no. or organisms

is controlled somewhat by the relationship between dissolved oxygen and temperature.

19.2 Solubility of gases in liquids Oil and vinegar

salad dressing separates because oil is not soluble in water.

Liquids that are not soluble in water may be soluble in other solvents.

19.2 Solubility rulesA set of solubility rules helps predict when an ionic compound is soluble or insoluble.

Investigation 19C

Key Question:How is the solubility of a gas affected by

temperature?

Solubility of CO2