2 chemistry questions please D: , another 10 points? ?

Question

I NEVER LEARNED THIS so can you explain each step done thank you :D

a) Determine the number of formula units in 0.670 mol AgNO3

b) What is the mass (in micrograms) of 2.39 x 1^20 formula units of Rb2SO4

THANK YOU SO MUCH!

Answer 1

AgNO3 is an ionic compound, so the purists call it a formula unit instead of a molecule; this is because an ionic compound doesn't contain molecules, it only contains ions. In AgNO3 the ratio of Ag+ and NO3- ions is 1:1, so we write the formula unit as AgNO3

1 mol contains 6.022x10^23 formula units of AgNO3.

0.670 mol contains 0.670x6.022x10^23 formula units = 4.035x10^23

Rb2SO4

1 mol of formula unit has a formula mass of-

2 Rb at 85.478 = 170.96

1 S at 32.06 = 32.06

4 O at 16.00 = 64.00  

170.96+32.06+64.00 = 267.02 g/formula unit

(2.38x10^20 / 6.022x10^23) x 267.02 g/formula unit = 0.000395 g

395 micrograms is the answer