Question

A solution containing 385.6 g of Mg(NO3)2 per liter has a density of 1.114 g/mL. The molarity of the solution is:

Answer 1

A solution refers to something (the solute) dissolved in water. Water has a density of 1.000 g/mL, but here the solution's density is 1.114 g/mL. That extra 0.114 g/mL must be coming from the solute!

Molarity is moles of solute per litre of solution (n/V), so let's convert g to n and mL to L. The molar mass of Mg(NO3)2 is 148.3 g/mol, so if we consider 1 mL of solution, the number of moles is 0.114/148.3 = 7.7 x 10^-4 mol. There are 1000 mL in a L, so there are 0.001 L (10^-3 L) in an mL. Now we can find the concentration:

7.7 x 10^-4 mol / 10^-3 L = 0.77 M

Please ask if you have any questions!

Answer 2

So does the 385.6 grams have nothing to do with anything?

Answer 3

My answer choices are:
A. 2.600
B.2.334
C.7.799
D.2.896
E. none

Answer 4

Ah give me one second. I didn't notice that the question said 385.6 g of Mg(NO3)2 PER LITER...

Answer 5

Ok this question actually becomes a bit easier because you don't need to worry about density (you would need this information if we were looking for molality). They question tells us how much solute is in a liter of solution, so we just need to find the moles of solute: 385.6/148.3 = 2.6 mol. Since this how much solvent is in 1 L, the molarity is 2.6 M and your answer is A!

Answer 6

Thank you so much!