A student used a carbon pencil to write his homework. The mass of this

1.	A student used a carbon pencil to write his homework. The mass of this was found to be 5 mg. With the help of this calculate.a. The number of moles of carbon in his homework writing. b. The number of carbon atoms in 12 mg of his homework writing.
Answer» (a). 5 mg carbon = 5 × 10 g carbon Atomic mass of carbon = 12 u ∴ Molar mass of carbon 12 g mol^-1 Number of moles = \(\frac{Mass\,of\,a\,subtance}{Molar\,mass\,of\,a\,subtance}\) = \(\frac{5\times 10^{-3}g}{12\,g\,mol^{-1}}\) = 4.167 x 10^-4 mol (b).12 mg carbon = 12 × 10^-3 g carbon Number of moles = \(\frac{Mass\,of\,a\,subtance}{Molar\,mass\,of\,a\,subtance}\) = \(\frac{12\times 10^{-3}g}{12\,g\,mol^{-1}}\) = 1 x 10^-3 mol Number of atoms = Number of moles × Avogadro’s constant Number of atoms of carbon = 1 × 10^-3mol × 6.022 × 10²³ atoms/mol = 6.022 × 10²⁰ atoms ∴ Number of moles of carbon in his homework writing = 4.167 × 10^-4 mol Number of atoms of carbon in 12 mg homework writing = 6.022 × 10²⁰ atoms

A student used a carbon pencil to write his homework. The mass of this was found to be 5 mg. With the help of this calculate.a. The number of moles of carbon in his homework writing. b. The number of carbon atoms in 12 mg of his homework writing.

Answer»

(a). 5 mg carbon = 5 × 10 g carbon

Atomic mass of carbon = 12 u

∴ Molar mass of carbon 12 g mol^-1

Number of moles = \(\frac{Mass\,of\,a\,subtance}{Molar\,mass\,of\,a\,subtance}\)

= \(\frac{5\times 10^{-3}g}{12\,g\,mol^{-1}}\)

= 4.167 x 10^-4 mol

(b).12 mg carbon = 12 × 10^-3 g carbon

Number of moles = \(\frac{Mass\,of\,a\,subtance}{Molar\,mass\,of\,a\,subtance}\)

= \(\frac{12\times 10^{-3}g}{12\,g\,mol^{-1}}\)

= 1 x 10^-3 mol

Number of atoms = Number of moles × Avogadro’s constant

Number of atoms of carbon = 1 × 10^-3mol × 6.022 × 10²³ atoms/mol

= 6.022 × 10²⁰ atoms

∴ Number of moles of carbon in his homework writing = 4.167 × 10^-4 mol

Number of atoms of carbon in 12 mg homework writing = 6.022 × 10²⁰ atoms