Exam 1 Review

Question 1

According to Henry’s Law, if the pressure increases to 2 atm and equilibrium is restored, which represents the equilibrium at 2 atm.

Answer 1

• The one where there are less gas molecules where there is 2 atm of pressure.
• the more pressure the gas has the more it will dissolve in the liquid.

Question 2

KI does not dissolve well in nonpolar solvents because…

Answer 2

• solute-solute interactions are much larger than solvent-solvent or solute-solvent.

Question 3

What are the major solute-solvent interactions created when HOCH2CH2OH dissolves in water?

Answer 3

• hydrogen bonding because a solute is bonding to water, which creates hydrogen bonding.

Question 4

What is expected to have the highest surface tension @ 25C?

Answer 4

• Which ever has the most OH- groups, the more OH- groups the higher its surface tension.

Question 5

BP os a liquid is 64C and the enthalpy change of this liquid to gas is 32.21 kJ/mol. What is the entropy, Svap?

Answer 5

• dS= dH/T

32.21/337.15 x 1000 = 95.5 J/mol * K

Question 6

Which has the highest viscosity?

Answer 6

• Which ever has the most OH- groups, the OH- groups the more viscous.

Question 7

What is the weight percent of vitamin C, in a solution made by dissolving 1.30 g of vitamin C, C6H8O6, in 55g of water?

Answer 7

• weight percent= mass of solute/total mas of solution x 100

1.3/(55+1.3) x 100 = 2.31%

Question 8

According to the diagram, the solid phase of this substance…

Answer 8

• is more dense than the liquid phase.

Question 9

The temperature and pressure at which all 3 phases can coexist in equilibrium…

Answer 9

• is wherever the 3 lines touch, because that is their equilibrium state.

.45atm & 130C

Question 10

How much heat is required to convert 3.12 moles of liquid benzene at 75.1C to gaseous benzene at 115.1C?

Answer 10

• Q= (n x Cm x dT) + (n x dH) + (n x Cm x dT)
• heat total = (heat required to get to boiling point) + (heat required to vaporize) + (heat required to get to gas)
• don’t forget to convert J to kJ

2.164 + 95.84 + 3.99 = 101.994 kJ

Question 11

What is the freezing point of a solution of 2.86 MgCl2 in 100 g of water? Kf for water is 1.86

Answer 11

• Tf = i x Kf x m
• i= van’t hoff factor
• m= molality (moles of MgCl2/mass of water in Kg) = .3
• 0 - 1.67, because is freezing

3 x 1.86 x .3 = 1.67, 0 - 1.67= -1.67

Question 12

How many cations M are in the unit cell?

Answer 12

• 1 because there is one on each corner and takes up 1/8 each

Question 13

What is the empirical formula of the mineral?

Answer 13

• M(8) x 1/8 (on the corners), M’(1) x 1 (it is in the center), A(6) x 1/2 (they are on the faces).

MM’A3

Question 14

What is the mole fraction of ethanol in a solution made by dissolving 7.3 g of ethanol, C2H5OH, in 53.6 grams of water?

Answer 14

• mole fraction formula: X= number of moles of ethanol/ (number of moles of ethanol + number of moles of water)
• Find the number of moles of each thing before plugging into formula

Question 15

Manganese crystallizes in a body centered cubic structure. What is the coordination number?

Answer 15

unit cells coord. # atom #
* simple unit cell 6 1
* body centered cubic 8 2
* face centered cubic 12 4
* cubic closest packed 12 4

8

Question 16

How many atoms are in one bosy-centered cubic unit cell of a metal?

Answer 16

2

Question 17

Germanium crystallizes in a face centered cubic unit cell and has an edge length of 452 pm. What is its density?

Answer 17

• face centered cubic unit cell has 4 atoms total (corners+face)
• mass of 1 unit cell = 4 x mass of Germanuim atom / Avogadros number
• volume of 1 unit cell = (edge length)^3 (and convert to cm (10^10)
• density = mass/volume

5.22 g/cm^3

Question 18

When 2.36g of a nonvolatile solute is dissolved in 100g of solvent, the largest change in freezing point will be achieved when the solvent is…

Answer 18

• dTf= Kf x m
• the greater the Kf value the more will be the decrease in freezing point

tert-butanol, Kf = 9.1

Question 19

An element forms a body-centered cubic crystalline substance. The edge of the cubic unit cell is 287pm, and the density of the crystal is 7.92 g/cm^3. Calculate the atomic weight of the substance.

Answer 19

• body centered cubic crystal has 2 atoms (center + corners
• volume = a^3, and convert pm to cm
• mass of unit cell = density x volume
• multiply by avogadros and divide my number of atoms

56.4 g

Question 20

What volume of a .716M KBr solution is needed to provide 10.5g of KBr?

Answer 20

• number of moles of KBr= weight of KBr/molar mass of KBr
• molarity = moles/ vol. in L
• Vol. in L = moles/Molarity

.08823 mol/.716 M = .123L = 123 mL

Question 21

When a liquid is heated at its boiling point, the…

Answer 21

• temperature of the liquid remains the same as long as any liquid is present

Question 22

Identify the packing shown in the figure below…

Answer 22

simple cubic

Question 23

Which of the following forms an ionic solid?

Answer 23

• metal + nonmetal = ionic solid

CsNO3

Question 24

Which of the following phase changes has a positive value for its entropy change?

Answer 24

• liquid to gas = dS increases
• solid to gas = dS increases
• solid to liquid = dS increases

creating steam

Question 25

KI crystallizes in a cubic unit cell with I- ions on each corvers and face. How many K+ and I- ions are in each unit cell of KI?

Answer 25

3 face and 1 on corner each = 4

4K+ ions and 4I- ions