Scratch Paper Chem. 111

Scratch paper

Chem. 111 Fall 2004 CLS NAME ______LAST FIRST EXAM III 100 POINTS - There are 5 pages to this exam SHOW ALL YOUR WORK. YOUR ANSWERS MUST HAVE THE CORRECT NUMBER OF SIGNIFICANT FIGURES AND UNITS. CORRECT SPELLING MUST BE USED . ______(14 pts.) 1. Fill in the blank: a. An emulsion can be destroyed/broken by adding ______

b. A liquid with weaker intermolecular forces will have a ______vapor pressure than

the vapor pressure above a liquid with stronger intermolecular forces.

c. The rates of evaporation will ______with substances with weaker intermolecular

forces.

d. Critical temperature of a gas is the ______temperature

______.

e. The ______is the pressure and temperature where solid, liquid, and

gas all coexist simultaneously.

f. An ______solution is a solution where additional solute will dissolve.

g. A ______from ______law occurs when the

intermolecular forces between A and B are weaker than the intermolecular forces between A—A and

the intermolecular forces between B-B.

h. Osmotic pressure for an FeCl2 aqueous solution will be ______than the osmotic

pressure for an aqueous solution of glycerin (polar molecule)

(8 pts.) 2. Write the total and net ionic equations for the following:

Molecular equation: K2S + Mn(NO3)3 --->

Total ionic______

3+ 2_ Net ionic______2 Mn (aq) + 3S 9aq)  Mn2S3(s)______

Molecular Equation: Sn(OH)4 + H3PO4 -->

Total ionic______

Net ionic____3Sn(OH)4(s) + 4H3PO4(aq)  Sn3(PO4)4(s) + 12 H2O (l)______

(18 pts.) 3. 2.00 L of 0.672 M Tin (V) nitrate is added to 3.00L of 0.775 M of Potassium carbonate

Sn(NO3)5 + K2CO3  Sn2(CO3)5 + KNO3

a. Write the total ionic equation

b. Calculate the mass of precipitate formed

ANSWER______249 g Sn2(CO3)5 ______e. Calculate the molar concentration of all species remaining in solution after the reaction has taken place.

Concentration of Tin(V) ions = 0.0824 M

Concentration of Nitrate ions = 1.34 M

Concentration of Carbonate ions = 0 M

Concentration of Potassium ions = 0.928 M

(12 pts.) 4. Methanol, CH3OH and ethanol, C2H3OH , form an ideal solution. The vapor pressure of pure ethanol is 56 torr. If a solution prepared from 90.0 g of methanol and 120.0 g of ethanol has a vapor pressure of 0.11 atm, what is the vapor pressure of pure methanol? {Molar mass of ethanol = 60.0, Molar mass of methanol = 45.0)

ANSWER______0.15 atm______(12 pts.) 5. A 2.770 M NaOH solution has a density of 1.109 g/mL. Express the concentration of this solution in molality.

ANSWER______2.775 m NaOH______Page 4 (15 pts.) 6. Hemoglobin contains 0.33 % Fe by mass. A 0.200 g sample of hemoglobin is dissolved in water to give 10.0 mL of solution, which has an osmotic pressure of 5.5 torr at 25.0 °C. How many moles of Fe atoms are present in one mole of hemoglobin.

ANSWER______4.0 mol Fe/1 mol Hemoglobin______

(15 pts.) 7. a. Calculate the Molar mass of Unknown “X” if : 1.60 g of unknown "X" dissolved in 100.0 g of cyclohexane produces a freezing point of - 5.1 °C. { cyclohexane has a freezing pt. =3.9 oC and the molal freezing point constant is 18.0). b. How many mL of unknown "X" (Density = 0.79 g/mL) needs to be dissolved in 50.0 g of water (Kb = 0.512) to make the boiling point of the resulting solution to be 104.5 °C if when unknown “X” dissolves in water to form 3 moles of ions for every mole of unknown “X” ?

ANSWER____a. 32 g X/mol______b. 5.95 mL “x”______Page 5 (3 pts.) 8. Define : Hydrophopic sol

(7 pts.) 9. On the phase diagram below:

Clearly Label: a. All the regions b. Both Axes

Draw a point on the phase diagram where you can clearly show how a solid can turn into a liquid and then into a gas without changing it’s pressure