A 4.691 g sample of MgCl₂ is dissolved in enough water to give 750. mL of solution. What is the magnesium ion concentration in this solution A) 3.70 * 10^-2 M B) 1.05 * 10^-2 M C) 6.57 * 10^-2 M D) 4.93 * 10^-2 M E) 0.131 M

Question

Quizplus · Accepted Answer

To find the magnesium ion concentration, we need to use the formula:

Mg ion concentration = moles of Mg / volume of solution

First, we need to find the moles of Mg in the sample of MgCl2. To do this, we'll need to use the molar mass of MgCl2:

Mg: 24.31 g/mol
Cl: 2 x 35.45 g/mol = 70.90 g/mol
Total molar mass: 95.21 g/mol

We have a 4.691 g sample, so we can find the moles:

moles of MgCl2 = 4.691 g / 95.21 g/mol = 0.04937 mol

This represents the moles of both magnesium ions and chloride ions, but we only want the magnesium ion concentration. Since MgCl2 dissociates into Mg2+ and 2Cl-, we know that for every one mole of MgCl2, we get two moles of Cl- and one mole of Mg2+. Therefore, the moles of Mg2+ in our sample is:

moles of Mg2+ = 0.04937 mol / 1 mol MgCl2 * 1 mol Mg2+ = 0.04937 mol

Finally, we can use this and the volume of the solution (750 mL = 0.750 L) to find the magnesium ion concentration:

Mg ion concentration = 0.04937 mol / 0.750 L = 6.57 x 10^-3 M = 6.57 x 10^10^-2 M = 6.57 x 10^-5 M = 6.57 x 10^5^-6 M = 6.57 x 10^11^-7 M

The answer with correct significant figures is C, 6.57 x 10^-3 M.

A 4691 G Sample of MgCl2 Is Dissolved in Enough Water

A 4691 G Sample of MgCl₂ Is Dissolved in Enough Water