$"Solute 1"$ , $"S1"$ , has a molecular mass of $40.0gmol^-1$ ...what is...?

Question

...what is $[S1]$ if a $4g$ mass of this material is dissolved in a $200mL$ volume of solution?

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Answer 1 · 2017-08-29T17:33:50

By definition, $"concentration"-="amount of stuff"/"volume of solution"$

And typically, we use $"molarity"-="moles of solute"/"volume of solution"$

And thus $"concentration of S1"$

$=((4*g)/(40.0*g*mol^-1))/(200*mLxx10^-3*L*mL^-1)=0.50*mol*L^-1$

And note the dimensionality of this solution....

We cancel out common terms in the numerator and denominator....

$=((4*cancelg)/(40.0*cancelg*mol^-1))/(200*cancel(mL)xx10^-3*L*cancel(mL^-1))=0.5*(1/(mol^-1))/L=0.50*mol*L^-1$

Why? Because $1/x^-1=1/(1/x)=x$ as required................