Question

calculează masa de apa necesara pentru a dilua 100g soluție de soda caustica de concentrație 20% pana la o concentrație de 10%​

Answer 1

 

$\displaystyle\bf\\\textbf{Aflam cantitatea de soda caustica din solutia initiala.}\\\\20\%~din~100g=20\%\cdot100=\frac{20}{100}\cdot100=20g~de~NaOH\\\\\textbf{Calculam cantitatea de solutie in care 20g~NaOH reprezinta 10\%.}\\\\10\%~din~S=20g\\\\\frac{10}{100}\cdot S=20g\\\\ S=20\cdot\frac{100}{10}\\\\ S=20\cdot10\\\\S=200g~cu~10\%~NaOH\\\\\textbf{Calculam cantitatea de apa}\\ \textbf{pe care trebuie s-o adaugam la solutia initiala.}\\\\200g-100g=\boxed{\bf100g~de~apa~trebuie~sa~adaugam.}$