Self Test for Unit 5: Chemical Quantities and Calculations

Part I: Multiple Choice with explanation: Choose the best answer and give an explanation that supports your choice

1.      How many oxygen atoms are in 10 formula units of Al2(SO4)3? (a) 10 atoms O        (b) 7 atoms O  (c) 70 atoms O  (d) 120 atoms O

2.      The mass of a mole of NaCl is the:  (a) gram formula mass.  (b) gram atomic mass.  (c) gram molecular mass.  (d) atomic mass.

3.      What is the molar mass of MgCl2?  (a) 59.8 g  (b) 95.3 g  (c) 125.8 g  (d) 76.4 g

4.      A large weather balloon filled with helium has a volume of 7.00 x 102 L at STP.  Which expression should be used to find the mass of helium in the balloon? (a)  22.4 L x 4 g He  (b) 7.00 x 102 x 4 g He  (c) 22.4 L/mol x 4 g He
mol            mol                           L                      mol                   7.00 x 102L     mol

(d)   7.00 x 102L x 4 g He
22.4 L/mol       mol

5.      Which of the following is not an empirical formula?  (a) Na2SO4  (b) C6H5Cl           (c) N2H4  (d) Sn3(PO4)4

6.      Which expression represents the percent by mass of nitrogen in NH4NO3?                (a) (14.0 g/80.0 g) x 100%  (b) (28.0 g/80.0 g) x 100%  (c) (80.0 g/14.0 g) x 100%  (d) 80.0 g/28.0 g) x 100%

7.      The empirical formula of a compound is CH2F.  The gram formula mass of this compound is 66.0 g.  The molecular formula of the compound is:  (a) C4H8F4          (b) C4H4F4 (c) C2H4F2 (d) CH2F

8.      Given that one molecule of phosgene, Cl2CO, contains two chlorine atoms, how many chlorine atoms are present in 2.00 moles of phosgene molecules? 
(a)  1.50 x 1023 atoms of chlorine   (b)  3.01 x 1023 atoms of chlorine  
(c)  6.02 x 1023 atoms of chlorine   (d)  1.20 x 1024 atoms of chlorine  
(e)  2.41 x 1024 atoms of chlorine

9.      The number of oxygen atoms in one molecule of H2SO4 is:  (a) 1  (b) 2  (c) 4  (d) 6  (e) 8

10.  If a sample of gaseous N2H4 contains 24 atoms of N, how many atoms of H are present? 
(a)  4  (b)  12  (c)  24  (d)  48  (e)  96

11.  If a sample of C2H6 contains 13 molecules, how many H atoms are present? (a)  6  (b)  12  (c)  13  (d)  78  (e)  104

Part 2: Problems – Solve the following problems in the space provided.  Remember to develop a system of showing your work, especially if you choose not to follow the problem solving method presented in class, your partial credit depends on this.

1.                  Find the mass of each of the following:

a.                  3.65 x 10-2 mol K2SO4

b.                  2.61 x 1024 molec. H2O2

c.                  0.060 L of CH4 gas at STP

d.            3.70 x 1022 atoms of Kr

2.                  Make the necessary conversion in the following:

a.       How many molecules are in 25.0 g of H2O?

b.      How many milliliters do 2.56 x 1021 atoms of He occupy at STP?

c.       How many formula units are present in a 1.34 nanogram sample of MgCl2?

3.                  What is the density of N2O, a gas at STP?

 

4.                  What is the percent composition of each of the elements in the following compounds?

  1. Cr2O3

 

  1. Experimental evidence of a compound indicates that a 18.35 g of the compound contains 5.74 g of tin and the rest is chlorine.

 

5.                  Determine the empirical formula of the compound with the percent composition of:  29.1% Na, 40.5% S, and 30.4% O.

 

6.                  A compound is 85.7% C and 14.3% H.  If the gram molecular mass of the compound is 42.0 g, find the molecular formula of the compound.

   

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