Question

What mass of barium chloride is required to make a `100*cm^3` volume of `0.25*mol*L^-1` solution with respect to `BaCl_2(aq)`?

Answer 1

Approx. `5*g`.........

Explanation:

`"Concentration"="Moles of solute (mol)"/"Volume of solution (L)"`

And thus the product `"volume"xx"concentration"="moles of solute."`

And thus..........

`n_(BaCl_2)=0.25*mol*L^-1xx100*cm^3xx10^-3*L*cm^-3`

`=0.025*mol` `BaCl_2`

And since `"no. of moles"="mass"/"molar mass"`

`"mass"=0.025*cancel(mol)xx208.23*g*cancel(mol^-1)=??g`

All I have done here is to use the given quotient that defines `"concentration"`, and divided or multiplied to give the quantity I want. As a check on my arithmetic, I included the units of each quantity. The fact that I clearly got an answer in `"grams"` for a question that asked for an answer in `"grams"` persuades me that I got the order of operations right (for once!).