1. Magnesium is an essential element for plants and animals. Someone comes up wi

Question

1.

Magnesium is an essential element for plants and animals. Someone comes up with an idea to use magnesium to precipitate iron in a small lake at the end of a short river that emerges from an iron mine. The idea is to sprinkle magnesium on the lake surface as well as dump it into the center of the lake. If the goal is to precipitate 50,000 grams of iron, what must the iron (III) chloride concentration of the river water be if it takes 32,645 g of magnesium metal filings to obtain that mass of iron, and the volume in which the solid forms is 100,000 L? 2FeCl3 (aq) +3Mg(s) 3MgCl2 (aq) +2Fe(s)

Explanation / Answer

2FeCl3 (aq) +3Mg(s) 3MgCl2 (aq) +2Fe(s)

Number of moles of Fe = amount in g / molar mass

= 50,000 grams of iron /55.85 g /moles

= 895.26 moles Fe

Now calculate the moles of FeCl3

895.26 moles Fe * 2 mole FeCl3 / 2 Mole Fe

= 895.26 moles FeCl3

Concentration of FeCl3 = number of mole / volume in L

= 895.26 moles FeCl3/ 100,000 L

= 8.95 *10^-3 M

if it takes 32,645 g of magnesium metal filings to obtain that mass of iron

Number of moles of Mg = amount in g / molar mass

= 32,645 grams ofMg /24.31 g /moles

= 1342.86 moles Mg

Now calculate the moles of FeCl3

1342.86 moles Mg * 2 mole FeCl3 / 3 Mole Mg

= 895.24 moles FeCl3

Concentration of FeCl3 = number of mole / volume in L

= 895.24 moles FeCl3/ 100,000 L

= 8.95 *10^-3 M

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