Show the setup to get to this: 29.8 grams of magnesium is equal to how many atoms of magnesium?

Answer 1

Hello, Mary,

This is where the concept of the mole comes in handy. One mole is 6.022x10²³ particles (atoms, molecules, paper clips, etc.) of anything. We want atoms. To find atoms we need to use the molar mass of Mg. Molar mass is the number of grams of that element or compond it takes to reach one mole of that item. The mole is tied to the atomic mass of the element or compound. The atomic mass of Mg is 24.3 AMU (atomic mass units). That also means that 24.3 grams of Mg contains 1 mole of atoms. That makes this a handy conversion factor:

(24.3g Mg/1 mole Mg), or 24.3 g/mole

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Now we can answer the question. We are given 29.8 grams of magnesium. To convert this to atoms of magnesium, divide the grams Mg by the molar mass of Mg. Note the units and how grams cancel, leaving just atoms.

(29.8 grams Mg)/(24.3g Mg/1 mole Mg) = 1.23 moles Mg

Now multiply 1.23 moles Mg times 6.022x10²³ atoms/mole to find atoms.

7.38x10²³ atoms of Mg

Bob