Question

a) find the mass of 10 moles of sodium sulphide.

b) calculate the number of molecules in 8g of oxygen gas.

please it's urgent...Exam tomorrow!!

Answer 1

ANSWER-1.  Molar mass of sodium sulphide = 78 g/mol
                                                   
                     Mass = No. of moles x Molar mass
                      m = n x M
                    = 10 x 78
                    = 780 g

Hence, 780 g is the  Mass of 10 moles of sodium sulphide.



ANSWER-2. Number of molecules
                              = given mass/molar mass x Avogadro number
                         atomic mass of oxygen = 16
               
molar mass of O2 molecules = 16 x 2 
                                                 = 32 g

⇒ number of molecules = 8/32 x 6.022 x 10²³
 
                                    ⇒  1.5055 x 10²³

Hence, 1.5055 x 10²³ is the number of molecules in 8g oxygen.

Answer 2

see attachment....

hope it will help u