Xét $100g$ thuỷ tinh
$m_{Na_2O}=100.13\%=13g$
$\to n_{Na_2O}=\dfrac{13}{62}=0,2097(mol)$
$m_{CaO}=100.11,7\%=11,7g$
$\to n_{CaO}=\dfrac{11,7}{56}=0,2089(mol)$
$m_{SiO_2}=100.75,3\%=75,3g$
$\to n_{SiO_2}=\dfrac{75,3}{60}=1,255(mol)$
$0,2097:0,2089:1,255=1:1:6$
Vậy CTHH thuỷ tinh là $Na_2O.CaO.6SiO_2$