CHM1310-001

Fall 2000

Exam #1 (100 pts.)

 

 

 

Name (Please print)________________________________

 

 

1.                  (10) Look at the periodic table in the front of the room.  Write the names of the first 20 elements in order of increasing atomic number.

 

Hydrogen, Helium, Lithium, Beryllium, Boron, Carbon, Nitrogen, Oxygen, Fluorine, Neon, Sodium, Magnesium, Aluminum, Silicon, Phosphorous, Sulfur, Chlorine, Argon, Potassium, Calcium

 

 

 

 

 

 

 

 

 

 

 

 

 

2.                  (10) Which prefix in the metric system would replace the following numbers given in powers of 10?

 

 

            10-3   milli

         

            106   mega

 

            10-6  micro

 

            10-2 centi

 

            103  kilo

 

 

3.                  (8) How many µg are in 0.0134 g?

(1.34 x 10-2 g) x 106 micrograms/g = 1.34 x 104 micrograms

 

 

 

4.         (6) An elemental ion has 22 protons, 20 electrons, and 26 neutrons. What

           isotope is it?

 

             4826Fe

 

             4726Fe

 

             4822Ti

 

             4822Ti2+  This one

 

             4822Ti2-

 

 

 

5.         (8) Use the periodic table to predict the product formed when strontium (Sr) combines with chlorine.

 

SrCl2

 

6.         The molecular formula of allicin, the compound responsible for the characteristic smell of garlic, is C6H10OS2.

 

a)      (10) How many moles of allicin are present in 5.00 mg of this substance?

Molar mass = (6x12) + (10x1) + (1x16) + (2x32) = 162 g/mole

 

(5x 10-3 g) x (1 mole/152 g) = 3.09 x 10-5 moles

 

 

 

 

 

 

 

 

            b)  (5) How many molecules of allicin are present in 5.00 mg of this substance?

 

(3.29 x 10-5 moles) x (6.02 x 1023 molecules/mole) = 1.86 x 1019 molecules

 

 

 

 

 

            c)  (5) How many sulfur atoms are present in 5.00 mg of this substance?

 

(1.86 x 1019 molecules) x (2 sulfur atoms/molecule) = 3.72 x 1019 sulfur atoms

 

 

 

 

 

 

 

 

 

7.         (16) Calcium hydride reacts with water to form calcium hydroxide and hydrogen gas.  Given the following unbalanced equation:

 

CaH2  +  2H2O  --->  Ca(OH)2 + 2H2

 

            How many grams of Ca(OH)2 are formed if 5.0 g of CaH2 are reacted?

 

(5.0 g CaH2) x (1 mole CaH2/42 g CaH2) = 0.12 moles CaH2

 

(0.12 moles CaH2) x (1 mole Ca(OH)2/1 mole CaH2) = 0.12 moles Ca(OH)2

 

(0.12 moles Ca(OH)2) x (74 g Ca(OH)2/mole Ca(OH)2) = 8.9 g Ca(OH)2

 

 

 

 

 

 

 

 

8.         One of the steps in the commercial process for converting ammonia to nitric acid involves the conversion of NH3 to NO:

 

4NH3(g) + 5O2(g) --> 4NO(g) + 6H2O(g)

 

            If 2.50 g of NH3 reacts with 2.85 g of O2

 

a)  (16) Which reactant is the limiting reactant?  (Show your work to justify your answer for credit.)      

 

If all the ammonia reacts how much NO is formed:

(2.50 g NH3) x (1 mole NH3/17 g NH3) = 0.147 moles NH3

(0.147 moles NH3) x (4 moles NO/4 moles NH3) = 0.147 moles NO

(0.147 moles NO) x (30 g NO/mole NO) = 4.41 g NO

 

If all the oxygen reacts how much NO is formed:

(2.85 g O2) x (1 mole O2/32 g O2) = 0.0891 moles O2

(0.0891 moles O2) x (4 moles NO/5 moles O2) = 0.0713 moles NO

(0.0713 moles NO) x ((30 g NO/mole NO) = 2.14 g NO

 

O2 is limiting reactant because it leads to less product.  Therefore O2 runs out before ammonia does.

 

 

 

 

 

            b)  (6) Calculate the theoretical yield of NO in grams.

2.14 g NO from above calculation