Question

a student used a carbon pencil to write his homework.the mass of these was found to be 5 mg.with the help of these calculate, the number of moles of cabon in his homework writing & the number of carbon atoms in 12 mg of his homework writing.​

Answer 1

Answer : The moles of carbon in his homework writing is, $4.167\times 10^{-4}mole$

The number of carbon atoms are, $6.022\times 10^{20}$

Explanation :

First we have to calculate the moles of carbon in 5 mg of carbon pencil in his homework writing.

Mass of carbon = 5 mg = 0.005 g    (1 mg = 0.001 g)

Molar mass of carbon = 12 g/mole

Formula used :

$\text{Moles of carbon}=\frac{\text{Mass of carbon}}{\text{Molar mass of carbon}}$

$\text{Moles of carbon}=\frac{0.001g}{12g/mole}=4.167\times 10^{-4}mole$

The moles of carbon in his homework writing is, $4.167\times 10^{-4}mole$

Now we have to calculate the number of carbon atoms in 12 mg of carbon pencil in his homework writing.

First we have to determine the moles of carbon.

Mass of carbon = 12 mg = 0.012 g    (1 mg = 0.001 g)

Molar mass of carbon = 12 g/mole

Formula used :

$\text{Moles of carbon}=\frac{\text{Mass of carbon}}{\text{Molar mass of carbon}}$

$\text{Moles of carbon}=\frac{0.012g}{12g/mole}=1\times 10^{-3}mole$

The moles of carbon in his homework writing is, $1\times 10^{-3}mole$

Now we have to determine the number of carbon atoms.

As, 1 mole of carbon contains $6.022\times 10^{23}$ number of carbon atoms

So, $1\times 10^{-3}$ mole of carbon contains $(1\times 10^{-3})\times (6.022\times 10^{23})=6.022\times 10^{20}$ number of carbon atoms

The number of carbon atoms are, $6.022\times 10^{20}$

Answer 2

Answer:

The number of moles of carbon in his homework writing. given wt =5mg=5×10−3g. =5×10−312=0.418×10−3moles =4.16×10−4moles.