1a) Answer is: the number of moles of gold (Au) in the sample is 0.178 mol.
m(Au) = 35.12 g; mass of gold.
M(Au) = 196.97 g/mol; molar mass of gold.
n(Au) = m(Au) ÷ M(Au).
n(Au) = 35.12 g ÷ 196.97 g/mol.
n(Au) = 0.178 mol; amount of gold.
1b) Answer is: the number of atoms of gold (Au) is 1.073·10²³.
N(Au) = n(Au) · Na.
N(Au) = 0.178 mol · 6.022·10²³ 1/mol.
N(Au) = 1.073·10²³.
2a) Answer is: 0.0035 moles of sucrose.
m(C₁₂H₂₂O₁₁) = 1.202 g; mass of sucrose.
M(C₁₂H₂₂O₁₁) = 12 · Ar(C) + 22 · Ar(H) + 11 · Ar(O) · g/mol.
M(C₁₂H₂₂O₁₁) = 12 · 12.01 + 22 · 1.01 + 11 · 16 · g/mol.
M(C₁₂H₂₂O₁₁) = 342.3 g/mol; molar mass of sucrose.
n(C₁₂H₂₂O₁₁) = m(C₁₂H₂₂O₁₁) ÷ M(C₁₂H₂₂O₁₁).
n(C₁₂H₂₂O₁₁) = 1.202 g ÷ 342.3 g/mol.
n(C₁₂H₂₂O₁₁) = 0.0035 mol; amount of sucrose.
2b) n(C) = 12·n(C₁₂H₂₂O₁₁).
n(C) = 12 · 0.0035 mol.
n(C) = 0.042 mol; amount of carbon in sucrose.
n(H) = 22·n(C₁₂H₂₂O₁₁).
n(H) = 22 · 0.0035 mol.
n(H) = 0.077 mol; amount of hydrogen in sucrose.
n(O) = 11·n(C₁₂H₂₂O₁₁).
n(O) = 11 · 0.0035 mol.
n(O) = 0.0385 mol; amount of oxygen atoms in sucrose.
2c) N(C) = n(C) · Na.
N(C) = 0.042 mol · 6.022·10²³ 1/mol.
N(C) = 2.53·10²²; number of carbon atoms in sucrose.
N(H) = n(H) · Na.
N(H) = 0.077 mol · 6.022·10²³ 1/mol.
N(H) = 4.63·10²²; number of hydrogen atoms in sucrose.
N(O) = n(O) · Na.
N(O) = 0.0385 mol · 6.022·10²³ 1/mol.
N(O) = 2.31·10²²; number of oxygen atoms in sucrose.
Na is Avogadro constant.
