Question

Calculati masa solutiei obtinuta prin amestecarea a 12g sare de bucatarie cu apa,daca solutia are concentratia 20%.Ce masa de apa a fost necesara?

Answer 1

$m_d=12g \ NaCl \\ \underline{cp=20\%} \\ m_s=? \\\\ \boxed{cp=\frac{m_d}{m_s}*100} \\\\ cp=\frac{100m_d}{m_s} \\\\ m_s=\frac{100m_d}{cp} \\\\ m_s=\frac{\not100*12g}{\not20} \\\\ m_s=5*12g \\\\ \boxed{\boxed{m_s=60g}} \\\\\\ cp=\frac{m_d}{m_d+m_{H_2O}}*100 \\\\ cp=\frac{100m_d}{m_d+m_{H_2O}} \\\\ m_d+m_{H_2O}=\frac{100m_d}{cp} \\\\ m_{H_2O}=\frac{100m_d}{cp}-m_d \\\\ m_{H_2O}= \frac{\not100*12g}{\not20}-12g \\\\ m_{H_2O}=5*12g-12g \\\\ m_{H_2O}=60g-12g \\\\ \boxed{\boxed{m_{H_2O}=48g}}}$