Question

A chemist prepares a solution of magnesium fluoride (MgF2) by measuring out 6.73mg of magnesium fluoride into a 250.mL volumetric flask and filling the flask to the mark with water. Calculate the concentration in mol/L of the chemist's magnesium fluoride solution. Round your answer to 3 significant digits.

Answer 1

We have to find the molarity of a solution of Magnesium Fluoride. The definition of molarity is:

Molarity = moles of solute/Volume of solution in L

Our solute is MgF₂:

Molarity = moles of MgF₂ / L of solution

From the problem we know that the volume of the solution that the chemist prepared is 250. mL, we will have to convert that into L.

We know that there are 1000 mL in 1 L. So:

1 L = 1000 mL

250. mL = 250. mL * 1 L/1000 mL = 0.250 L

Volume of solution in L = 0.250 L

Now we have to find the number of moles of MgF₂ that the chemist added. From the problem we know the mass of MgF₂ added. Let's convert it to g:

1000 mg = 1 g

mass of MgF₂ = 6-73 mg

6.73 mg = 6.73 mg * 1 g/1000 mg = 0.00673 g

mass of MgF₂ = 0.00673 g

When we want to find the number of moles that we ave in a certain amount of a compound, we have to use the molar mass. Let's find the molar mass of MgF₂.

According to the periodic table the atomic mass of Mg is 24.3 amu and the atomic mass of F is 19 amu. So the molar mass of MgF₂ is:

molar mass of MgF₂ = 24.3 + 2 * 19 = 62.3 g/mol

molar mass of MgF₂ = 62.3 g/mol

Using the molar mass we can find the number of moles that we have in 6.73 mg or 0.00673 g of MgF₂:

moles of MgF₂ = 0.00673 g/(62.3 g/mol)

moles of MgF₂ = 1.08 * 10^-4 moles

So the chemist added 1.08 * 10^-4 moles of MgF₂ in 0.250 L of solution. Then the molarity of the solution is:

Molarity = moles of solute/Volume of solution in L

Molarity = 1.08 * 10^-4 moles/0.250 L

Molarity = 4.32 * 10^-4 M

So the answer to our problem is 4.32 * 10^-4 M