mHF =\(\frac{40 . 2,5}{100 }\) = 1kg
\(\begin{gathered} {\text{Ca}}{{\text{F}}_{\text{2}}}\xrightarrow{{H = 80\% }}2HF \hfill \\ 78\,kg\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,40\,kg \hfill \\ x\,kg\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,1\,kg \hfill \\ \Rightarrow x = \frac{{1.78}}{{40}} = 1,95\,kg \hfill \\ \end{gathered} \)
\(m_{CaF_{2}}\) = \(\frac{1,95. 100}{80}\) = 2,4375 kg
