Ch 13 Solutions

Question 1

Air is a solution, what is the solvent and the major solute?

Answer 1

Solvent is nitrogen

Majority solute is oxygen

Question 2

3 types o f Solutions?

Answer 2

1) Gas - Formed by gas/gas
2) Solid - Formed by solid/solid
3) Liquid - Formed by liquid/gas, liquid/solid, or liquid/liquid

Question 3

True or False? Gases are always soluble in each other?

Answer 3

True

Question 4

Define Miscible

Answer 4

When two substances are soluble in each other in all proportions

Question 5

What is the solubility of NaCl in 100g of water?

Answer 5

36g at 25 deg Celsius

40g at 100 deg Celsius

Question 6

What is the “Chemists Rule of Thumb”?

Answer 6

Like dissolves like - Polar molecules and ionic compounds will dissolve in polar solvents. Non polar molecules will dissolve in non polar solvents.

Question 7

Textbook examples of exothermic and endothermic reactions?

Answer 7

1) Exothermic - When NaOH is dissolved in water, heat is released and the container gets hot.
2) Endothermic - When NH4NO3 dissolves in water, heat is absorbed from the surroundings and the container gets cold.

Question 8

4 common textbook Polar Solvents?

Answer 8

1) Water (H2O)
2) Acetone (CH3COCH3)
3) Methanol (CH3OH)
4) Ethanol (CH3CH2OH)

Question 9

4 Common textbook Non-Polar Solvents?

Answer 9

1) Hexane (C6H14)
2) Diethyl Ether (CH3CH2OCH2CH3)
3) Toluene (C7H8)
4) Carbon Tetrachloride (CCl4)

Question 10

Define Enthalpy

Answer 10

The sum of the internal energy of a system and the product of its pressure and volume; the amount of energy associated with the breaking and forming of bonds in a chemical reaction.

Question 11

Define Enthalpy (heat) of Reaction

Answer 11

The Enthalpy change for a chemical reaction

🔺Hsoln = 🔺Hsolute+🔺Hsolvent + Hmix

Question 12

What is the Heat of Hydration? 🔺Hhydration

Answer 12

The combination of 🔺Hsolvent and 🔺mix.

Question 13

If |🔺Hsolute | < |🔺H hydration| then then the reaction is ______?

Answer 13

The reaction is negative and therefore exothermic.

Question 14

If |🔺Hsolute | > |🔺H hydration| then then the reaction is ______?

Answer 14

The reaction is positive and therefore endothermic.

Question 15

If |🔺Hsolute | = |🔺H hydration| then then the reaction is ______?

Answer 15

The reaction is equal therefore neither exothermic nor endothermic.

Question 16

What is the opposite of dissolving? What are it’s practical use?

Answer 16

Recrystallization - it’s a good way of purifying substances.
Purification involves dissolving a solid in a hot solvent until the solution is saturated and as the solution SLOWLY cools, the solid crystallizes out, leaving the impurities behind.

Question 17

What is the significance of the Solubility Curve of Solids?

Answer 17

It’s a graph that shows that for most Solids, the solubility of the solid increases as the temperature increases.

Question 18

What is one exception to the Solubility Curve of Solids?

Answer 18

Cesium Sulfate Ce2(SO4)3

It’s solubility decreases as the temperature increases.

Question 19

Define Saturated, Unsaturated and Supersaturated?

Answer 19

1) Saturated - When a solution has the solute and solvent in dynamic equilibrium; if you add more solute, it will not dissolve.
2) Unsaturated - A solution that has less solute than saturation; more solute will dissolve at this temp.
3) Supersaturated - A solution that has more solute than saturation.

Question 20

How can a solvent hold more solute beyond dynamic equilibrium? aka supersaturation?

Answer 20

Saluting can be made saturated at no-room conditions and then allowed to come to room conditions slowly. For some solutes, instead of coming out of solution when the conditions change, they get stuck between the solvent molecules and the solution becomes supersaturated.
Supersaturated solutions are unstable and lose all the solute above saturation when disturbed.
i.e. shaking a carbonated beverage

Question 21

Give and example of a Supersaturated Solution and it’s practical use?

Answer 21

Sodium Acetate NaC2H3O2 - used for heating packs. Can hold a Supersaturated state for a long time if not disturbed/cracked.

Question 22

How does the temperature of solvent affect the solubility of gases?

Answer 22

For ALL gases, the solubility of the gas decreases as the temperature increases (the opposite of Solids).

Question 23

How does the solubility of gasses in water compare to ionic and polar Covalent Solids’ solubility in water?

Answer 23

Gases generally have lower solubility in water than ionic or polar Covalent Solids because most are non polar molecules.

Question 24

Explain Henry’s Law

Answer 24

Henry’s Law (Sgas = kH Pgas) - States that the solubility of a gas (Sgas) is directly proportional to its pressure (Pgas).

Question 25

What are the Henry’s Law Constants for the following gases in water at room temperature (25 degrees celsius):
O2
N2
CO2
NH3
He

Answer 25

1) O2 = 1.3 x 10 ^ -3
2) N2 = 6.1 x 10 ^ -4
3) CO2 = 3.4 x 10 -2
4) NH3 = 5.8 x 10 ^ 1
5) He = 3.7 x 10 ^ -4

Question 26

Why is Henry’s Law Constant for Ammonia (NH3) so much larger than most other gases?

Answer 26

Because it is polar and will dissolve better in water (also polar) than most other gases that aren’t.

Question 27

Define Concentration

Answer 27

Amount of solute in a given solution

Question 28

How does the calculation for molality differ than the rest of the concentration calculations?

Answer 28

Molality is calculated using solute/solvent, whereas most other concentration calculations uses solute/solution. Where solution = solute + solvent.

Question 29

How do you calculate Mole Percent?

Answer 29

Mole Percent = Mole Fraction x 100

Question 30

How do you calculate percent by mass?

Answer 30

Solute/(Solute+Solvent)

Question 31

Define Colligative Properties?

Answer 31

Properties whose values depend only on the number of solute particles and not the on what they are.
Value of the the property depends on the concentration of the solution.

Question 32

What are the four Colligative Properties discussed in the textbook?

Answer 32

1) Lower Vapor Pressure
2) Lower Freezing Point
3) Higher Boiling Point
4) Osmotic Pressure

Question 33

Describe Raoult’s Law?

Answer 33

The vapor pressure of a solution = the mole fraction of the solvent times the vapor pressure of the solvent at the same temperature.

Question 34

Describe Vapor Pressure Lowering

Answer 34

The difference between the vapor pressure of the the pure solvent and the vapor pressure of the solvent in solution.

Question 35

How do you calculate Kelvin?

Answer 35

Kelvin = Degrees In Celsius + 273

Question 36

How do you convert from atm to torr(mmhg)?

Answer 36

1 atm = 760 torr(mmhg)

Question 37

What is the value of R that represents the ideal gas constant of (atm-L)/(mol-K)?

Answer 37

R = 0.08206

Question 38

Examples of isotonic solutions?

Answer 38

5% glucose

0.9% NaCl

Question 39

What is crenation?

Answer 39

When RBCs shrink and shrivel up. Usually caused by hypertonic fluid outside the RBC that cause all the water to leave the cell via osmosis.

Question 40

Describe the molecular make-up is soap?

Answer 40

Soap is a fatty acid that forms a colloid with a hydrophilic/ionic head and a hydrophobic/nonpolar tail.

Question 41

What are the 5 types of Colloidal Dispersions?

Answer 41

1) Aerosol - Fog (water droplets in air)
2) Solid Aerosol - Smoke (ash in air)
3) Foam - Whipped Cream (air bubbles in butter fat)
4) Emulsion - Milk (milk fat globules in water)
5) Solid Emulsion - Opal (water in Silica glass)

Question 42

Describe Miscelle Formation?

Answer 42

I.E. when soap forms a colloid, the head attract water molecules and the tails turn away forming a “bubble like structure”.

Question 43

How do you calculate Freezing Point Depression and Boiling Point Elevation?

Answer 43

FPD = molality x Kf

BPE = molality x Kb