How many grams are there in 7.4 x 1023 molecules of h2so4?

7.4x10^23 = molecules of silver nitrate sample  

6.022x10^23 number of molecules per mole (Avogadro's number)  

Divide molecules of AgNO3 by # of molecules per mol  

7.4/6.022 = 1.229 mols AgNO3 (Sig Figs would put this at 1.3)  

(I leave off the x10^23 because they both will divide out)  

Use your periodic table to find the molar weight of silver nitrate.  

107.868(Ag) + 14(N) + 3(16[O]) = 169.868g/mol AgNO3  

Now multiply your moles of AgNO3 with your molar weight of AgNO3  

1.229mol x 169.868g/mol = 208.767g AgNO3

answer : a model is often used to explain and make things easier to understand when any scientific topic needs to be demonstrated and explained.

as in this case where a scientist wants to use a model to present the results of his detailed scientific investigation. he should do it as it will him to make the audience understand the concept in a much better way. also, it can be changed according to new scientific understandings.