# Mass of strontium iodide contained in a 350 mL solution

What mass (in mg) of strontium iodide is contained in $350\ \mathrm{mL}$ of a strontium iodide solution that has a concentration of $1.93\ \mathrm{µM}$?

What I have done:

$0.350\ \mathrm{L}\ \ce{SrI_2}\cdot \frac{1.93\cdot 10^{-6}}{1\ \mathrm{L\ Solution}}\cdot \frac{341.42\ \mathrm{g}\ \ce{SrI2}}{1\ \mathrm{mol}\ \ce{SrI2}}=2.31\cdot 10^{-4}~\mathrm{g}~\ce{SrI2}=0.231~\mathrm{mg}~\ce{SrI2}$

What is not correct here?

• Why did you ask this question? Was that your answer in a test and it was marked as incorrect? Because the numeric value in the end seems to be correct, however I as a teacher would mark it as wrong, too, for incorrect use of units.
– Jan
Commented Dec 9, 2015 at 10:19
• I did write the correct units when I did the problem (just wrong on here), but it got marked completely wrong on a test, without any explanation. Commented Dec 16, 2015 at 4:57

The mistake is that you didn't write "mol" after $1.93 \times 10^{-6}$.