Critical item 3:

(N_A = 6.022 x 10²³ mol^-1)

1 How many molecules are there in 15.0 mole of ethane?                                     answer
 

2 Calculate the number of molecules there are in 45.0 grams of ethane (C₂H₆).      answer

3 What is the mass of 1.80 x 10²⁶ atoms of iron?                                                    answer
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

1
 

N = N_A n            N_A = 6.022 x 10²³ mol^-1

N =  6.022 x 10²³ mol^-1  x 15.0 mol

N =  9.03 x 10²⁴  (molecules)
 
 

2

(M stands for molar mass.)

M = m / n

M(C₂H₆) = 30.0 g mol^-1

30.0 g mol^-1  =  45.0 g / n

 m = 1.50 mol

N = N_A n            N_A = 6.022 x 10²³ mol^-1

N =  6.022 x 10²³ mol^-1  x 1.50 mol

N =  9.03 x 10²³  (molecules)

3

16.7 kg