Problem Set 3.7:       Mole Review

Complete each question on your own sheet of paper. Show your work using unit analysis where necessary.

1.       Convert 500.0 g NaCl to formula units. 5.15 x 1024 f.u.   

2.       Convert 9.8 x 1024 molecules of C2H6 to grams. 4.9 x 102 g     

3.       The mass of an unknown gas is 11.59 g. The mass of an equal volume of He is 1.45 g. Calculate the molar mass of the unknown gas. 31.93 g/mol 

4.       Calculate the percentage composition of sulphur in Al2(SO4)3. 28.11%  

5.       Calculate the molar mass of Co2(SO4)3•6H2O    514.16 g/mol 

6.       The empirical formula for a compound is C2H5O and its molecular mass is 135 g/mol. Determine the molecular formula. C6H15O3 

7.       A compound is 24.4% Ca, 17.1% N and 58.5% 0. Calculate the empirical formula. CaN2O6 

8.       Find the number of atoms in 7.6 g of sodium phosphide.

7.6 g  x   1 mol  x  6.02 x 1023 molecules  x   4 atoms Na3P   =  1.8 x 1023 atoms 

              99.94 g             1 mol                          1 molecules 

9.       How many C atoms in 60.5 g of sucrose? C12H22O11 molar mass = 342.34 g/mol

60.5g x   1 mol    x  6.02 x 1023 molecules  x   12 atoms C  =  1.28 x 1024 atoms 

              342.34 g               1 mol                      1 molecules

10.    If 3.75 x 1024 atoms of hydrogen are found in a sample of ammonium chloride, what mass of ammonium chloride is present? NH4Cl    M= 53.50 g/mol

3.75 x 1024 atoms H  x  1 molecule  x            1 mol             x   53.50 g    =   83.3g  

                                        4 atoms H         6.02 x 1023 molec        1 mol  

11.    How many molecules in

       a) 7.56 g of bromine gas.

7.56 g  x     1 mol     x    6.02 x 1023 molecules    =    2.85 x 1022 molecules   

                 159.80 g                  1 mol   

       b) 88.55g of carbon monoxide gas.

88.55 g    x    1 mol      x  6.02 x1023 molecules     = 1.90 x 1024 molecules   

                     28.01 g                    1 mol    

       c) 18.6L of chlorine gas (at STP)

18.6L x     1 mol      x      6.02 x 1023 molecules  =  5.00 x 1023 molecules    

                 22.4 L                        1 mol    

       d) 1.56 x 103 L of methane gas at STP.

1.56 x 103 L    x    1 mol    x   6.02 x 1023 molecules    =    4.19 x 1025 molecules    

                             22.4 L                     1 mol    

12.    What volume at STP would

       a) 6.85 x 1022 molecules of sulphur dioxide take up.

6.85 x 1022 molecules    x                 1 mol                   x       22.4 L     =     2.55 L    

                                              6.02 x 10 23 molecules              1 mol    

       b) 68.7 g of helium take up.

68.7 g    x   1 mol       x   22.4 L     =   385 L    

                   4.00 g            1 mol    

       c) 1.78 mol of mercury gas take up.

1.78 mol     x     22.4 L      =     39.9 L    

                           1 mol    

       d) 7.51 x 10 25 molecules of nitrogen gas take up

7.51 x 1025  molecules  x                   1mol                x   22.4 L     =   2.79  x  103 L    

                                              6.02  x  1023 molec             1 mol    

13.    a) How much would 3.42 x 103L of oxygen (held at STP) weigh?

3.42 x 103 L   x    1 mol          x       32.00 g     = 4.89 x 103 g   

                             22.4 L                   1 mol

       b) How many atoms of oxygen would be found in the above quantity of gas.

3.42 x 103L  x  1 mol x  6.02 x 1023molecules x  2 atoms O  = 1.84 x 1026 atoms 

                         22.4 L                 1 mol                 1 molecule       

14.    How much mass and volume (at STP) of gaseous tetraphosphorus hexaoxide would be present if 9.63 x 1024 atoms of oxygen were found in the sample?

9.63 x 1024 atoms   x  1 molecule   x          1 mol            x        219.88 g  =  586 g 

                                     6 atoms O      6.02 x 1023 molecules       1mol    

 

9.63 x 1024 atoms x  1 molecule   x        1 mol                       x  22.4 L  = 59.7 L

                                    6 atoms O       6.02 x 1023 molecules      1 mol    

15.    If the mass of a stone is 2.603 kg, and that of a pencil is 5.15 g, calculate the mass of the stone relative to that of the pencil. 505 times larger 

16.    If the mass of a lithium atom is 6.94 amu, and that of a uranium atom is 238.1 amu, calculate the mass of the lithium atom relative to that of the uranium atom. 34.3

17.    Calculate the number of fluorine atoms in 4.25 moles of fluorine gas. 5.12 x 1024 atoms

18.    Calculate the number of moles of methane in 8.71 x 1022 molecules of methane. 0.145 mol Calculate the number of atoms of hydrogen present in this same sample of methane. 3.49 x 1023 atoms  Calculate the number of moles of hydrogen atoms present in the sample. 0.580 mol

19.    How many moles are present in 288.9 g of sodium carbonate, Na2CO3? 2.726 mol

20.    What mass of Fe(NO3)2 is present in 0.0157 mole of this substance? 2.824 g

21.    What is the molarity of a solution made by adding to 295.6 g of potassium sulfide, K2S, sufficient water to make 10.00 L of solution? 0.2681 M

Extra Practice Questions (will be counted for Bonus in a homework check!!)

22.    Sulfur combines chemically with oxygen to produce an oxide of sulfur. Determine the empirical formula of this compound, given that 22.7 g of the sulfur produces 45.3 g of the sulfur oxide. SO2

23.    A 7.00 g sample of a molecular compound whose molar mass is 32.0 g/mol is analyzed, and is found to yield 6.13 of nitrogen and 0.87 of hydrogen. Determine the empirical and molecular formulas of the compound. N2H4

24.    18.48 g of carbon and 58.52 g of fluorine are obtained from the analysis of a molecular compound whose molar mass is 150.0 g/mol. a) Determine the empirical and molecular formulas of the compound. CF2 C3F6          b) Calculate the percent composition of carbon and of fluorine in the compound. 23.91 % C and 76.09 % F 

25.    How many grams of magnesium chloride, MgCl2, are contained in 755 mL of a 0.64 M solution? 46 g

26.    75.7 g of lithium chloride, LiCl, is diluted with sufficient water to make a 0.885 M solution. Calculate the volume of this solution. 2.02 L   

27.    What volume of 0.84 M magnesium chloride solution contains in 5.50 g of magnesium chloride? 0.069 L

28.    What mass of elemental chlorine contains the same number of atoms as does 24.0 grams of carbon?   70.9 g

29.    How many moles of atoms are there in 1.20 x 1025 carbon tetrachloride, CCl4, molecules?  99.7 moles

30.    How many moles of nickel atoms are needed to supply the same number of atoms as does 10.0 grams of neon? 0.496 mol 

31.    How many grams of lithium are needed to supply twice as many atoms as does 27 grams of beryllium? 20.8 g 

32.    Calculate the molarity of a solution formed by dissolving 67.4 g KCl in sufficient water to make 2.50 L of solution. 0.361 mol/L

33.    How many atoms are contained in 28.0 grams of gaseous nitrogen? 1.20 x 1024 atoms 

34.    0.500 mole of an element has a mass of 31.75 grams. Identify the element. copper 

35.    What is the mass of 2.11 x 1024 molecules of chlorine gas? 249 g 

36.    31.0 grams of rust is composed of 21.7 grams of iron. The other element in rust is oxygen. Determine the empirical formula for rust. Fe2O3  

37.    A sample of carbon reacts with a 9.2 g sample of hydrogen to form a gaseous compound that has a mass of 120.0 grams. CH What is the molecular formula of this hydrocarbon, which has a molar mass of 26.0 grams? C2H2

38.    Calculate the percent by mass of calcium and chlorine in CaCl2. 36.11 % Ca and 63.89 % Cl