Question

How many atoms are in .1785 mmol magnesium?

Answer 1

Hint: A mole is a quantity that denotes 6.022$\times {{10}^{23}}$atoms, also called an Avogadro number. Every 1 mole of an element contains this number of atoms.

Complete answer:
We have been given the amount of magnesium in millimoles as .1785 mmol. We have to calculate the total number of atoms in this amount of magnesium.
For this, we have to convert millimoles into moles.
1 mole = 1000 millimoles
1 mmol = $\dfrac{1}{1000}$ moles
.1785 mmol = $\dfrac{.1785}{1000}$moles
.1785 mmol = 0.0001785 moles = 1.785$\times {{10}^{-4}}$ moles
So, .1785 millimoles are 1.785$\times {{10}^{-4}}$ moles.
Now, as we know, 1 mole of magnesium contains 6.022$\times {{10}^{23}}$atoms per mol, so we have to multiply 1.785$\times {{10}^{-4}}$ moles into 6.022$\times {{10}^{23}}$atoms /mol to get the number of atoms in given magnesium.
So, number of atoms in .1785 mmol of Mg = 1.785$\times {{10}^{-4}}$ moles $\times $ 6.022$\times {{10}^{23}}$atoms/mol
Total atoms = 1.0749$\times {{10}^{20}}$atoms
Hence, .1785 millimoles of magnesium contain 1.0749$\times {{10}^{20}}$atoms.

Additional information:
Irrespective of magnesium, if we take the amount of any element, then the total number of atoms in that amount of element will always be the amount of element multiplied by the Avogadro number of atoms per mole (6.022$\times {{10}^{23}}$).

Note:
Millimoles are a smaller unit of moles, and considered as a thousandth part of moles. It is used in detection of very small quantities in medical tests. The conversion of millimole into mole is, 1 mmol = 0.001 moles.