7. Tetraphosphorous trioxide has which molecular formula? A. 4P3O B. P 3 O 4 C.

Question

7.         Tetraphosphorous trioxide has which molecular formula?

            A.        4P3O

            B.         P3O4

            C.         P4O4

            D.        P4O3

9.         What is the mass of a metal that displaces 1.296 mL of water and has a density of 9.43 g/cm3?                                

            A.        0.1374 g

            B.         0.137 g

            C.         12.2 g

            D.        12.22 g

10.       Your protocol requires you measure 100 mL of a solution. The most appropriate vessel to use is

            A.        A 100 mL beaker

            B.         A 500 mL graduated cylinder

            C.         A 100 mL graduated cyclinder

            D.        A 250 mL beaker

11.       How many molecules are in 42 moles of nitrogen gas?            

      A.        588 molecules

      B.         1176 molecules

      C.         6.8 x 10-23 molecules

      D.        2.5 x 1025 molecules

12.       How many grams are in 42 moles of nitrogen gas?                                                                              

      A.        588 g

      B.         1176 g

      C.         6.8 x 10-23 molecules

      D.        2.5 x 1025 molecules

For questions 13-14, use the information provided below from the experiment Identification of an Unknown. The molecular masses and reactions are provided for you.

NaHCO3           KHCO3                        Na2CO3                        K2CO3              NaCl                KCl          

84.01 g/mol     100.12 g/mol   105.99 g/mol   138.21 g/mol   58.44 g/mol     74.55g/mol

2 NaHCO3 (s) à Na2CO3 (s) + H2O (g) + CO2 (g)                    (Reaction 1)

Na2CO3 (s) +2HCl (aq) à 2NaCl (s) + H2O (l) + CO2 (g)          (Reaction 2)

13.       Brad starts with 0.652 g of unknown. How much mass should he have after the first heating step if his unknown
            was NaHCO3?

            A.        0.411 g Na2CO3

            B.         0.326 g Na2CO3

            C.         0.822 g Na2CO3

            D.        0.00402 g Na2CO3

If Brad has a final mass of 0.270 g at the end of the experiment (after the 2nd heating), what is his percent yield
            of the final salt? (Assuming he starts with 0.652 g of NaHCO3).

A. 40%    B.60%   C. 80%    D. 86%

Explanation / Answer

7. D. P4O3

9. mass = density*volume = 9.43*1.296 = 12.22 grams

D. 12.22 g

10. C. A 100 mL graduated cyclinder

11. 1 mole = 6.023*10^23 molecules

   42 mole = 42*6.023*10^23 = 2.53*10^25 molecules .

D.2.5 x 1025 molecules

12. mass of 42 mole N2 = 42*28 = 1176 gram

B. 1176 grams

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