Sapling HW #6

[Brandon McClelland3L]

I'm having a lot of trouble with one of the problems on Sapling, but I don't know what my error is.

The question is:
If 6.72 g of CuNO3 is dissolved in water to make a 0.420 M solution, what is the volume of the solution in milliliters?

First, I calculate number of moles by doing:
6.72/187.56 = 0.0358...

I then plug that in to a shifted around version of the molarity equation:
0.0358.../0.420 = 0.0853 L

Change to mL:
85.3 mL

What am I doing wrong?

[Hayden Lee 1C]

Based on the math I can see here, it looks like you are solving the problem properly. Check to see if the molar mass of CuNO3 that you calculated is correct (this is the only thing that I can see potentially causing this issue). Other than that, everything looks completely fine to me.

[Agustina Santa Cruz 2F]

Hi! I was having the same issue. I think the molar mass that you used at the beginning was wrong. 187.56 is what google says but if you add all of them up separately you get 125.55. Try that?

[Constance Newell]

If you add the masses you should get 125.55 g. Then you should be able to find the mol. With the mol, you can set up a proportion to find ml:
(mol1)(ml1)=(mol2)(ml2)

[Brandon McClelland3L]

You were right, I messed up calculating the molar mass. Thanks!

[Adam_ElSayed_3B]

When I did this problem I made a lot of mistakes, such as mistaking the correct decimal points, but just double check that all ur calculations are right and youll be fine. Get the molar mass, and then anonther mistake I made was put v=m/n instead of v=n/m so watch out for stupid miscalculations.

[Kainalu Puu-Robinson]

Like Agustina said, if you try to google the molar mass of CuNO3 it will tell you its 187.56 g/mol. This is actually the molar mass of Cu(NO3)2 and not CuNO3 like the problem is asking. Just be careful and double check that you're using the molar mass of the right chemical equation.

[Jose Miguel Conste 3H]

Hi, most likely your molar mass is wrong as the molar mass is 125.55 g

[Savannah Torella 1L]

I think you may have calculated the molar mass of CuNO3 incorrectly. Using the periodic table, 63.546+14.007+(3*15.999)= 125.55gmol^-1. Hope that helps!