Question

1. Calculate the formula mass of calcium iodite Ca(IO2)2 in amu.

2. Calculate the number of atoms in a 2.93x10^23g sample of silicon.

3. How many atoms are in 0.920g of P2O5?

4. What is the mass (in grams) of 9.92x10^24 molecules of methanol (CH3OH)?

Answer 1

1) Ca(IO2)2

Ca = 40.078

I = 126.904 = 2 I = 2 x 126.904 = 253.808

O = 15.999 = 4 O = 4 x 15.999 = 63.996

total = 40.078 + 253.808 + 63.996 =357.88

answer = 357.88 amu

2) Si = 28.08 g/mol

28.08 g Si contain 6.023 x 10²³ Si atoms

2.93 x 10²³ g Si contain 2.93 x 10²³ x 6.023 x 10²³ / 28.08 = 6.28 x 10⁴⁵ atoms

answer = 6.28 x 10⁴⁵ atoms

3) 141.94 g P2O5 contain 7 x 6.023 x 10²³ atoms

0.920 g P2O5 contain 0.92 x 7 x 6.023 x 10²³ / 141.94 = 2.73 x 10²² atoms

answer = 2.73 x 10²² atoms.

4) 6.023 x 10²³ molecules = 32 g

9.92 x 10²⁴ molecules = 9.92 x 10²⁴ x 32 / 6.023 x 10²³ = 5.27 x 10² g

answer = 5.27 x 10^{2 g}