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?

  • 3
    $\begingroup$ 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. $\endgroup$
    – Jan
    Commented Dec 9, 2015 at 10:19
  • $\begingroup$ 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. $\endgroup$ Commented Dec 16, 2015 at 4:57

1 Answer 1


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

Some teachers/professors might let that go, others wouldn't, depending upon what they are really trying to teach you.

Units and dimensional analysis are important.


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.