Honors Chemistry Chapter 16 Notes - Solutions

Honors Chemistry Chapter 16 Notes - Solutions (Student edition)

Chapter 16 problem set: 49, 54, 55, 57, 77, 78, 81-83, 87-89, 91

16.1 Properties of Solutions

Mixtures -A combination of kinds of matter, each retains its own .

Homogeneous: a mixture with composition (ex: water).

Heterogeneous: a mixture without composition (ex: water).

Solutions - A homogeneous mixtures in a single .

Properties: 1) distribution of particles 2) won’t 3) 4) can’t be (small particle size)

Two parts to a solution:

Solute: the part that gets dissolved. Solvent: the part that does the dissolving.

Aqueous: (aq) a solution that contains as the solvent.

Tinctures: solutions that contains as the solvent.

Examples: I2 in alcohol, phenolphthalein solution

Types of Solutions

Type of Solution Example Gas with gas liquid with liquid solid with solid Brass, (metallic solution), amalgam (mercury solution) solid with liquid gas with liquid gas with solid Hydrogen in platinum Antifreeze - It is used to keep water from in a radiator (ethylene glycol).

1 Hydrometer: used to measure the of a liquid.

Specific Gravity: Sg = density of the /density of

Solubility degree and rate of solution

Degree of Solubility: the amount of substance required to form a saturated solution in a certain amount of solvent at a certain temperature.

solute + solvent ↔ solution ( )

If you wish to dissolve a substance, you can help by:

1. 2. 3.

Solubility depends on:

1. The nature of the solute and solvent:

Polar/ionic versus nonpolar

2. Temperature

For most solids, solubility increases as temperature

Graph for solids:

Solubility grams solute 100 g H2O

Temperature oC

For gases, solubility decreases as temperature . (think )

2 a graph to explain soda and dead fishies......

Graph for gases: Hey – label each axis!

3. Pressure ( only)

As pressure increases, solubility .

Henry’s law: solubility is proportional to .

Effervescence: the escape of a gas from a solution.

Graph for gases:

Solubility, the nature of solute and solvent, and the energy changes during solution formation

Dissolving an ionic compound in water:

Na+ Cl- Cl- Na+ O-2

+ H+ H+  Cl- Na+ O-2 Na+ Cl- H+ H+

Step #1 Step #2 Step #3 Breakup the Breakup the Formation of the

( ) ( ) ( )

If step #1 plus step #2 are more than step #3, then the overall reaction is .

3 Energy Level Diagram:

Energy (most solutions are )

Time (solution process)

If step #1 plus step #2 are less than step #3, then the overall reaction is .

Energy Level Diagram: Hey – You label each axis!

Heat of Solution: The amount of heat when a solute dissolves in a solvent.

Heat of Hydration: energy when are surrounded by molecules.

The # of water molecules used depends on the .

↑ Heat released (more ) as the size of the ion

Li+1 -523 kJ/mole versus Na+1 -418 kJ/mole

↑ Heat released (more ) as the charge of the ion

Na+1 -418 kJ/mole versus Mg+2 -1949 kJ/mole

Li and Mg are close to the same size, so...

- separation of ions - the process of solute particles caused by the action of the solvent. being surrounded by water Remember: polar/ionic dissolves polar/ionic ( ).

4 O2 and CO2 are nonpolar. They don’t dissolve very much in water (just enough for sodas and fishies).

Solubility curves and tables

soluble (definition): more than 1 g of solute dissolves per 100 g of water slightly soluble: between 0.1 and 1 g dissolves insoluble: less than 0.1 g dissolves

d = ni - - not been found to form

Saturated, unsaturated, and supersaturated solutions

Saturated Solution: holds as much solute as it can at a given temperature and certain amount of solvent.

must be stated when determining solubility.

For gases, must also be stated when determining solubility.

Unsaturated Solution: the solution is currently dissolving than the maximum amount of solute at a given temperature.

Saturated with undissolved salt: The solution holds the maximum amount of solute for certain conditions and some extra solute settles to the bottom.

Supersaturated Solution: the solution currently holds than the maximum amount of solute at a given temperature.

How is this possible? These solutions are created by saturating a hot solution and allowing it to .

example - sodium acetate and Na2S2O3 (sodium thiosulfate) “hypo” to printers

Now it’s time to do some sample problems with reading solubility graphs. There are three skills to know: a) how to read a graph b) ratio and proportion and c) subtraction

Dilute Vs. Concentrated – show with graphs

: a small amount of solute in a large amount of solvent.

5 : a large amount of solute in a small amount of solvent.

Do not confuse with .

16.2 Concentrations of Solutions

Molarity A method used to calculate concentration.

Molarity (M) =

When you talk about a solution with a label of 6 M HCl, we say, “ Six molar solution.”

Molality Another method used to calculate concentration.

molality (m) =

When you talk about a solution with a label of 6 m HCl, we say, “ Six molal solution.”

The dilution formula: = ( = )

Ex: What is the molarity of a solution made by adding 35.0 ml of a 6.00 M HCl solution to 100.0 ml of water?

6.00 M 100 ml HCl + water = 35 ml 135 ml ? M HCl

% Solution Example: Suppose we have a solution that contains 50.0 ml of alcohol (solute) and 50.0 ml of water (solvent). If the density of the alcohol is 0.800 g/mL, calculate the following percent solutions. General Formula  (solute/solution)100 = %

6 Three ways to calculate the % solution:

#1 Volume of solute x 100  Volume of solution

#2 Weight of solute x 100 Volume of solution

#3 Weight of solute x 100 Weight of solution

16.3/16.4 Colligative Properties of Solutions and Calculations

Freezing point depression

Solutions that conduct electricity contain electrolytes. Ionic compounds :

NaCl(s) + H2O(l) yields

MgCl2(s) + H2O(l) yields

Acids (dissociation of a covalent compound):

HCl(g) + H2O(l) yields

H2SO4(l) + H2O(l) yields

Substances that are not acids, bases, and salts do not dissociate/ionize. When solutes dissolve in liquids, they the freezing point.

Two factors affect the degree of change in the temperature: the amount of the and the nature of the .

Colligative properties: a property that depends on the . Freezing point and boiling point are colligative properties.

7 ∆tf = kf (m) book formula - not true ∆tf = kf (m)(x) true x = # of produced when the solute dissolves

o kf water = -1.86 C/m

Why does freezing point depression occur?

O Na+ O

H H ………… O ………… H H

H H Cl-

The solute (NaCl) interferes with crystal formation. (ex: antifreeze) As the number of solute particles increase, the freezing point .

Boiling point elevation

Same concept as freezing point depression except boiling point .

o kb water = 0.512 C/m Why does boiling point elevation occur? The solute takes up space on the of a liquid. This decreases the ability of the liquid to . Thus, the vapor pressure . Boiling occurs when the atmospheric pressure the vapor pressure. So, an in energy is needed to increase the vapor pressure to reach the atmospheric pressure.

= solvent versus = solute

“A” “B”

Which would produce more vapor?

Which would have a higher vapor pressure?

Which would take less energy to raise the vapor pressure to atmospheric pressure?

8 Which would have a higher boiling point?

Ex1: Calculate the boiling point of a solution of 10.00 grams of NaCl in 200.0 grams of water. Calculate the freezing point of the same solution.

NIB Ion Pairing

When experiments are done regarding freezing point depression and boiling point elevation, the actual answers are different than the answers (surprise, surprise!).

9 Example: a solution of NaCl in water:

Concentration Actual change in the Theoretical change in % dissociation (molality) freezing point the freezing point .1 - 0.346 - 0.372 .01 - 0.0361 - 0.0372 .001 - 0.00366 - 0.00372 .0001 - 0.000372 - 0.000372

Sodium Chloride can dissociate at a rate of 100% if the concentration of the solution is very . With increased concentration, ions may come in contact with each other and resulting in than 100% dissociation. Only at low, low concentrations do solutions have their approach the theoretical value.

A picture of ion pairing:

Theoretical: Actual:

Na+ O Cl- O Na+ O Cl- Na+ O Cl- O Na+ O Cl- Cl- O Na+ O Cl- O Na+ Cl- O Na+ O Cl- O Na+ O Cl- O Na+ O Cl- O O Cl- O Na+ O Cl- O O Na+ O Cl- O Na+ O Na+ O Cl- O Na+

X = 14 ions X = 10 “ions”

10 Ex1: What is the solubility of potassium chlorate at 50.0 oC in 100.0 ml of water?

20.0 g of potassium chlorate in 100.0 grams of water

Ex2: What temperature will result in a saturated solution of 80.0 grams of sodium nitrate and 100.0 grams of water?

10.0 oC

Ex3: If 40.0 grams of ammonium chloride are placed in 100.0 grams of water at 50.0 oC, is the solution saturated or unsaturated? If saturated, how much salt remains undissolved? If unsaturated, how much more salt can be dissolved?

The solution is unsaturated and can hold 10.0 more grams of ammonium chloride.

Ex4: If 80.0 grams of potassium nitrate are placed in 100.0 grams of water at 44.0 oC, is the solution saturated or unsaturated? If saturated, how much salt remains undissolved? If unsaturated, how much more salt can be dissolved?

The solution is saturated with 10.0 grams of ammonium chloride undissolved.

Ex5: What is the solubility of lithium sulfate at 90.0 oC in 50.0 ml of water?

At this temperature the 100.0 ml of water can hold 30.0 grams of this salt. So, if half as much water is present, half as much salt will dissolve. Show the math:

30.0 g = x

11 100.0 ml 50.0 ml

x = 15.0 grams of lithium sulfate in 50.0 grams of water

At this temperature the 100.0 ml of water can hold 30.0 grams of this salt. So, if twice as much water is present, twice as much salt will dissolve. Show the math:

30.0 g = x 100.0 ml 200.0 ml

x = 60.0 grams of lithium sulfate in 200.0 grams of water

At this temperature the 100.0 ml of water can hold 30.0 grams of this salt. So, if 68.2 % of the water is present, 68.2% of the salt will dissolve. Show the math:

30.0 g = x 100.0 ml 68.2 ml x = 20.5 grams of lithium sulfate in 68.2 grams of water