How do I determine the empirical formula of each of these compounds?

Question

What's the empirical formula if a sample contains...

(a) .104 mol K, .052 mol C, .156 M O

(b) 5.28 g SN, 3.37 g F

(c) 87.5% N and 12.5% H by mass

Answer 1

(a)

.104 mol K / 0.52 = 2 moles K

.052 mol C / 0.052 = 1 mole C

.156 M O / 0.052 = 3 moles O

your answer is: K2CO3

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(b)

5.28 g Sn / 118.7 = 0.044 moles Sn

3.37 g F / 19 = 0.177 moles F

0.044 moles Sn / 0.044 = 1 mole Sn

0.177 moles F / 0.044 = 4 mole F

your answer is : SnF4

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(c)

87.5% N / 14 = 6.25 moles N

12.5% H / 1.01 = 12.4 moles H

6.25 moles N / 6.25 = 1 mole N

12.4 moles H / 6.2 = 2 mole H

your answer is NH2