Answer to Question #199479 in Biology for ARCHIE MEDINA

Question

1. Determine the number of atoms in 1.75 mol Al

2. Calculate the number of formula units in 25.0 mol NaNO3

3. Given 6.25 mol H O2 determine the number of molecules.

DIRECTIONS: A. How many atoms are in each of the following samples?

a atoms Ne

b molecules CH4

1. What is the percent composition of the following compounds?

a Naphtalene (C10 H8)

b Sucrose (C12 H22 O11)

c Alu um sulfate Al2(SO4)3

Answer 1

1. N(Al) = n(Al) × N_A = 1.75 mol × 6.022 × 10²³ = 1.05 × 10²⁴ atoms

2. N(NaNO₃) = n(NaNO₃) × N_A = 25.0 mol × 6.022 × 10²³ = 1.50 × 10²⁵ formula units

3. N(H₂O) = n(H₂O) × N_A = 6.25 mol × 6.022 × 10²³ = 3.76 × 10²⁴ molecules

4. a. One mole of Ne contains 6.022 × 10²³ atoms;

b. one mole of CH₄ contains 6.022 × 10²³ molecules and 3.01 × 10²⁴ atoms

5. a. Mr(C₁₀H₈) = 128 g/mol; %(C) = (12 g/mol × 10) / 128 g/mol = 0.9375 = 93.75 %; %(H) = 100 % - 93.75 % = 6.25 %

b. Mr(C₁₂H₂₂O₁₁) = 342 g/mol; %(C) = (12 g/mol × 12) / 342 g/mol = 0.421 = 42.1 %; %(H) = 22 g/mol / 342 g/mol = 0.064 = 6.4 %; %(O) = 100 % - 42.1 % - 6.4 % = 51.5 %

c. Mr(Al₂(SO₄)₃) = 342 g/mol; %(Al) = (27 g/mol × 2) / 342 g/mol = 0.158 = 15.8 %; %(S) = (32 g/mol × 3) / 342 g/mol = 0.281 = 28.1 %; %(O) = 100 % - 15.8 % - 28.1 % = 56.1 %.