Question

how many grams of Cl are in 265g CaCl2 ?

Answer 1

At the first, we need to find the mass fraction of ${{\text{Cl}}}$ in ${{\text{CaC}}{{\text{l}}_{\text{2}}}}$. To do so we need to find the molar mass of ${{\text{CaC}}{{\text{l}}_{\text{2}}}}$ - it can be calculates as the sum of atomic weights taking into account the number of atoms of each type.

$${M_{{\text{CaC}}{{\text{l}}_{\text{2}}}}} = {M_{{\text{Ca}}}} + 2{M_{{\text{Cl}}}} = 40.08[\frac{{\text{g}}}{{{\text{mol}}}}] + 2 \cdot 35.45[\frac{{\text{g}}}{{{\text{mol}}}}] = 110.98[\frac{{\text{g}}}{{{\text{mol}}}}]$$

(atomic weights of atoms ${{\text{Ca}}}$ and ${{\text{Cl}}}$ can be found in periodic table and respectively equal to $40.08[\frac{{\text{g}}}{{{\text{mol}}}}]$ and $35.45[\frac{{\text{g}}}{{{\text{mol}}}}]$)

Then we can find the mass fraction by dividing the sum of atomic weights of all ${{\text{Cl}}}$ atoms by molecular mass of ${{\text{CaC}}{{\text{l}}_{\text{2}}}}$

$$\omega = \frac{{2{M_{{\text{Cl}}}}}}{{{M_{{\text{CaC}}{{\text{l}}_{\text{2}}}}}}} = \frac{{2 \cdot 35.45[\frac{{\text{g}}}{{{\text{mol}}}}]}}{{110.98[\frac{{\text{g}}}{{{\text{mol}}}}]}} = 0.64$$

And let's find the mass of ${{\text{Cl}}}$ by multiplying the mass fraction by mass of ${{\text{CaC}}{{\text{l}}_{\text{2}}}}$

$${m_{{\text{Cl}}}} = \omega {m_{{\text{CaC}}{{\text{l}}_{\text{2}}}}} = 0.64 \cdot 265[{\text{g}}] = 169.6[{\text{g}}]$$