Respuesta :
Sometimes, when working with ionic compounds like magnesium chloride we talk about formula units instead of molecules, but they are similar.
We are asked for the number of formula units (or molecules) of MgCl₂ that we have in 26.2 g of it.
Before we determine the number of formula units, we have to convert 26.2 g into moles. To do that we will use the molar mass of MgCl₂.
atomic mass of Mg = 24.31 amu
atomic mass of Cl = 35.45 amu
molar mass of MgCl₂ = 24.31 + 2 * 35.45
molar mass of MgCl₂ = 95.21 g/mol
moles of MgCl₂ = mass of MgCl₂/(molar mass of MgCl₂)
moles of MgCl₂ = 26.2 g/(95.21 g/mol)
moles of MgCl₂ = 0.275 moles
Once that we know the number of moles of MgCl₂ that we have in our sample, we can find the number of formula units. According to Avogadro's number, we have 6.022*10^23 formula units in 1 mol of formula units. We will use that conversion to get the answer to our problem.
1 mol of MgCl₂ = 6.022 *10^23 formula units
formula units of MgCl₂ = 0.275 moles of MgCl₂* 6.022 *10^23 formula units/(1 mol of MgCl₂)
formula units of MgCl₂ = 1.66 *10^23 formula units
Answer : 1.66 * 10^23 formula units make up 26.2 g of magnesium chloride.
