Ch. 6 moles & empirical formula        test       40 points                                                          chemistry

Show your work in an organized manner, include (i) any relevant equation (or formula), (ii) conversion factor(s), (iii) put the proper units in your calculations and answer, and (iv) have the proper number of significant figures in your answer.

1.  Solve.  [10 points]

a.  275 grams of water  =  __ moles of water

b.  2.5 moles of Ca(NO3)2  =  __ g Ca(NO3)2

2. What is the empirical formula of a compound containing 0.0130 moles carbon, 0.0390 moles hydrogen, and 0.0065 mol oxygen ?  [5 points]

3.  What is the chemical formula of a compound with a molar mass of 51.5 g / mol with an empirical formula of NH2Cl ?  [5 points]

4.  The combustion of 2.78 mg of a compound containing carbon, hydrogen, and oxygen produced 6.32 mg of carbon dioxide and 2.58 mg of water.   [20 points]

a.  How many grams of C are in the compound ?  [hints:  # g C in compound = # g C in CO2;  what’s % C in CO2 ?]

b.  How many grams of hydrogen are in the compound ?

c.  How many grams of oxygen in the compound ?

d. How many moles of C, H, and O in the compound ?

 

 

 

  1. What’s the empirical formula of the compound ?