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Question
Solve problem:
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 the number of moles of carbon in his homework writing.
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Solution
5 mg carbon = 5 × 10-3 g carbon
Atomic mass = 12 u
∴ Molar mass of carbon = 12 g mol-1
No. of moles = `"Mass of substance"/"Molar mass of substance"`
= `(5 xx 10^-3)/(12 "g" "mol"^-1)`
= 4.167 × 10-4 mol
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