Chemical Calculations - 1

Chemistry Level 2

Calculate the total number of atoms in 0.5 moles of potassium dichromate $(\text{K}_2\text{Cr}_2\text{O}_7).$

If your answer is $1.04 \times 10^{23},$ write it as 1.04E+23.

1 solution

Joshua Chin
Apr 4, 2016

Using avogadro's number, $0.5 mol$ of a compound contains $0.5\cdot 6.02\cdot 10^{ 23 }=3.01\cdot 10^{23}$ molecules.

In potassium dichromate, ${ K }_{ 2 }{ Cr }_{ 2 }{ O }_{ 7 }$ , there are $2+2+7=11$ atoms in a molecule of ${ K }_{ 2 }{ Cr }_{ 2 }{ O }_{ 7 }$ .

Hence there are $11\cdot3.01\cdot10^{23}=3.31\cdot10^{24}$ atoms per $0.5$ moles of ${ K }_{ 2 }{ Cr }_{ 2 }{ O }_{ 7 }$