3. How many grams of magnesium ion are in 155.0 grams of Mg3P2?

83.82 g of magnesium ions.

Explanation:

We want to determine the mass of magnesium ions in 155.0 grams of magnesium phosphide (Mg₃P₂).

We can convert from grams of Mg₃P₂ to moles of Mg₃P₂, moles of Mg₃P₂ to moles of Mg, and moles of Mg to grams of Mg.

Find the molecular weight (molar mass) of magnesium phosphide:

The molecular weight of magnesium is 24.31 g/mol*.

From the chemical formula, we can see that there are three moles of magnesium for every one mole of magnesium phosphide.

Hence, multiply initial amount with known ratios:

In conclusion, there are 83.82 grams of magnesium ions in 155.0 grams of magnesium phosphide.

*Because the magnesium ions in magnesium phosphide have two less electrons, its molecular weight will indeed be lower. However, due to the extremely small size of an electron (1/2000th of a proton), the difference in mass is insignificant.