Q.) Determine the concerntration of a solution made by dissolving 10.0g of sodium chloride in 750.0ml of solution.

I did the following; 1mol of sodium chloride = 58.44

  • 58.44*10 - 584.4g
  • Concentration = number of moles/volume
  • 584.4/0.750 = 779.2 - and this is the wrong answer.

Any pointers would be appreciated.

  • 1
    $\begingroup$ Rather than doing operations on just the numbers, also pay attention to the units; carry them along in your calculations. Do you see any mistakes? $\endgroup$ – Nicolau Saker Neto Dec 6 '15 at 21:22
  • 2
    $\begingroup$ I should have divided - 10/58.44 and then divided that by .750 - thank you for your comment. $\endgroup$ – Anasutashia Dec 6 '15 at 21:24

The molar mass $M$ of $\ce{NaCl}$ is $58.44\ \mathrm{\frac{g}{mol}}$ indeed:

$\displaystyle\text{molar mass}(\ce{NaCl}) = \frac{\text{mass}}{\text{amount of substance}} = 58.44\ \mathrm{\frac{g}{mol}}$

$\displaystyle\Rightarrow \text{amount of substance} = \frac{\text{mass}}{\text{molar mass}}=\frac{10.0\ \mathrm g}{58.44\ \mathrm{\frac{g}{mol}}} \approx 0.171\ \mathrm{mol}$

$\displaystyle\text{concentration} = \frac{\text{amount of substance}}{\text{volume}}=\frac{0.171\ \mathrm{mol}}{0.75\ \mathrm L}=0.228\ \mathrm{\frac{mol}{L}}$

Assumptions: Adding $\ce{NaCl}$ to these $750\ \mathrm{ml}$ does NOT change the volume noteworthy.

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