A student wants to have 3.011 × 1023 atoms each of magnesium and carbon elements. For this purpose, he will have to weigh :(a) 24 g of magnesium and 6 g of carbon(b) 12 g of carbon and 24 g of magnesium(c) 20 g of magnesium and 10 g of carbon(d) 12 g of magnesium and 6 g of carbon

Academic Chemistry NCERT Class 9

Correct Answer: (d) 12 g of magnesium and 6 g of carbon

Explanation: 12 g of carbon and 24.3 g of magnesium, each contains 6.022×10²³ number of atoms.

Let X g of carbon have 3.011×10²³ number of atoms.

Therefore,

X= $\frac {molar \ mass \ of \ carbon × number \ of \ atoms \ of\ carbon} {Avogadro \ number}$

X =12×3.011×10²³ / 6.022×10²³

X=6 g of carbon

So, 6 g of carbon contains 3.011×10²³ number of atoms.

Now,

Let X g of magnesium have 3.011×10²³ number of atoms.

Therefore,

X= $\frac {molar \ mass \ of \ magnesium × number \ of \ atoms \ of\ magnesium} {Avogadro \ number}$

X=24 × 3.011×10²³/ 6.022×10²³

X=12 g of magnesium

So, 12 g of magnesium contains 3.011×10²³ number of atoms.

Therefore, the student will weigh 12 g of magnesium and 6 g of carbon.

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Updated on: 10-Oct-2022

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