# Question a8838

Feb 3, 2015

Since no information was given on the volume of the bottle, I'll do the calculations using a $\text{1-L}$ bottle. Moreover, you don't mention what the bottle is labeled as containing $\text{56.2 ppm}$. To be a little more specific, I don't know what's in the bottle to begin with.

So, I'll show you how to determine the molarity of a solution that has $\text{56.2 ppm}$ of ${\text{Fe}}^{3 +}$ ions. What ppm - parts per million - means is that you have miligrams of solute in liter of solution. A $\text{1 ppm}$ solution would mean that you have

$\text{1 ppm" = ("1 mg")/("1 L") = ("0.001 g")/("1000 mL}$

This means that a $\text{56.2 ppm}$ solution will have

"56.2 ppm" = ("56.2 mg")/("1 L") = ("0.0562 g")/("1000 mL")

In order to determine molarity you need moles of solute per volume of solution. Since you know that you have $\text{0.0562 g}$ of ${\text{Fe}}^{3 +}$ present, use iron's molar mass to determine how many moles you have

${\text{0.0562 g" * ("1 mole Fe"^(3+))/("55.85 g") = "0.00101 moles Fe}}^{3 +}$

This means that the solution's molarity is

C = n/V = ("0.00101 moles")/("1 L") = "0.00101 mol/L" = "0.00101 M"#

The molarity of the solution is so small that you can express it as $\text{mmol/L}$, or $\text{mM}$ (milimoles per liter, or milimolar)

$C = \text{1.01 mmol/L" = "1.01 mM}$