Question

A student weighs out a 5.69 g sample of , transfers it to a 250. mL volumetric flask, adds enough water to dissolve it and then adds water to the 250. mL tick mark.What is the molarity of magnesium sulfate in the resulting solution?

Answer 1

We will convert the volume of the solvent from mL to L, then we will calculate the mass concentration:

`\begin{gathered} volume:250mL*(1L)/(1000mL)=0.25L \\ \\ mass\text{ }conc.=(mass)/(volume) \\ \\ mass\text{ }conc.=(5.69g)/(0.25L) \\ mass\text{ }conc.=22.76gL^(-1) \end{gathered}`

We will convert the mass concentration to molar concentration:

`\begin{gathered} molar\text{ }conc.=\frac{mass\text{ }conc.}{molar\text{ }mass(MgSO_4)} \\ \\ molar\text{ }conc.=\frac{22.76\text{ }gL^(-1)}{120.366\text{ }gmol^(-1)} \\ \\ molar\text{ }conc.=0.189\text{ }molL^(-1) \end{gathered}`

Answer: Molarity of MgSO4 is 0.189M.