Question

What is the volume of 1.5M HCl needed to acquire 4.5g of HCl?

Answer 1

Assuming the mass we have is only of HCl, not the whole solution, we can do the following steps:

- Use the molar mass of HCl to see how many moles of HCl correspond to 4.5g of HCl.

- Use the concentration of 1.5 M to see how much volume have the calculated number of moles of HCl.

To calculate the molar mass of HCl, we need the molar masses of H and Cl, which we can get from a periodic table:

`\begin{gathered} M_H=1.00794g\/mol \\ M_(Cl)=35.453g\/mol \\ M_(HCl)=1\cdot M_H+1\cdot M_(Cl) \\ M_(HCl)=(1\cdot1.00794+1\cdot35.453)g\/mol \\ M_(HCl)=(1.00794+35.453)g\/mol \\ M_(HCl)=36.46094g\/mol \end{gathered}`

So, using it, we can calculate the number of moles of HCl in 4.5g of HCl:

`\begin{gathered} M_(HCl)=(m_(HCl))/(n_(HCl)) \\ n_(HCl)=(m_(HCl))/(M_(HCl)) \\ n_(HCl)=(4.5g)/(36.46094g\/mol)=0.123419\ldots mol \end{gathered}`

Since concentration is number of moles of solute divided by the volume of solution, we have:

`\begin{gathered} \lbrack HCl\rbrack=(n_(HCl))/(V)_{} \\ V=(n_(HCl))/(\lbrack HCl\rbrack) \\ V=(0.123419\ldots mol)/(1.5mol\/L)=0.082279\ldots L=82.279\ldots mL\approx82mL \end{gathered}`

So, to get 4.5 g of HCl from a solution of 1.5 M of HCl, we need approximately 82 mL.