Department of Chemistry

CARNEGIE MELLON UNIVERSITY

09-105 MASTERY EXAM I
January 19, 1999 Section

Show all work.

This EXAM must be returned.

NAvog. = 6.022 X 1023 mol-1

1 L = 1000 cm3 = 10-3 m3

 

 

Element

Atomic Weight
     
 

H

1.008
 

Li

6.941
 

B

10.811
 

C

12.01
 

N

14.01
 

O

16.00
 

Na

22.99
 

Cl

35.45
 

K

39.10
 

As

74.92
 

I

126.90
 

Hg

200.59

 

 

1.

 __________/25
 

2.

 __________/25
 

3.

 __________/25
 

4.

 __________/25
 

Total

 __________/100

 

 

1. Lithium borate is a solid compound that is used in the preparation of certain enamels. Its chemical analysis shows it to be 25.57% boron (B), 8.21% lithium (Li) and 66.22% oxygen (O) by mass. Consistent with the precision of these values, what is the empirical formula for lithium borate? (Show all work.)

2. The atomic masses of 10B and 11B are 10.013 amu (atomic mass units) and 11.009 amu, respectively. A sample of boron from a nuclear reactor laboratory is analyzed and found to have an average atomic weight of 10.887 amu. Calculate the percent abundances by mass of each boron isotope in this sample. (Show all work.)


3. Potassium nitrate (KNO3), also known as saltpeter, is employed in fertilizer, fireworks, pickling meats and treating tobacco among other uses. Ingestion of large quantities may cause violent gastroenteritis. It is produced through the reaction, unbalanced, shown below.

KCl + HNO3 + O2 KNO3 + Cl2 + H2O

Calculate the minimum mass of chlorine gas (Cl2) that will be produced during the production of each 1000 g of KNO3.

4. Veterinarians use Donovan's solution to treat skin diseases in animals. The solution is prepared by mixing 1.00 g of AsI3, 1.00 g of HgI2, and 0.900 g of NaHCO3 in enough water to make a total volume of 100.0 mL. Compute the total mass of iodine per liter of Donovan's solution, in grams per liter.

 

 

How many atoms of iodine are in one liter of Donovan's solution?