Question

Find out the molar concentration of a 500 ml solution, which contains 20 grams of $CaB{r}_2$ (formula weight = 200).

• A. $0.1$ molar
• B. $0.2$ molar
• C. $0.5$ molar
• D. $1$ molar
• E. $5$ molar

Answer 1

Answer: (B)

$0.2$ molar

The number of moles is the ratio of mass to molar mass.
Number of moles of $CaB{r}_2=\frac{20g}{200g/mol}=0.1moles$
The molar concentration is the ratio of the number of moles of solute to volume of solution (in L).
The molar concentration of $CaB{r}_2=\frac{0.1moles}{500mL\times 0.001L/mL}=0.2molar$