Stannous fluoride, SnF_2, is added to toothpaste to prevent tooth decay. How man

Question

Stannous fluoride, SnF_2, is added to toothpaste to prevent tooth decay. How many germs of fluoride are in a 4.50 mole sample of SnF_2? a. 9.00 g b. 171 g c. 42.8 g d. 85.5 g e. 342 g For questions 10 & 11, consider the following Lewis structure for carbonyl sulfide (0CS). What are the formal charges on the oxygen atom, carbon atom, and sulfur atom, respectively? a. + 1, 0, - 1 b. - 1, 0, + 1 c. - 2, + 4, - 2 d. 0, 0, 0 Is the provided Lewis structure the best possible structure for 0CS? a. No, there is an equivalent resonance form that is just as good. b. No, there is a different Lewis structure that is even better. c. Yes, it has the fewest units of formal charge. d. Yes, it has the formal charge distributed according to electronegativity.

Explanation / Answer

9)

1 mol of SnF2 has 2 mol of F

So,

mol of F = 2*number of moles of SnF2

= 2*4.50 mol

= 9.00 mol

molar mass of F = 19 g/mol

mass of F = molar mass of F * number of mol of F

= 19 g/mol * 9.00 mol

= 171 g

Answer: b

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