24 gm of silicon dioxide were heated with 28.8 gm of magnesium. When the obtained product was treated with hydrochloric acid 6.72 litres of hydrogen measured at S.T.P. were collected. Determine the mass of isolated silicon. The reactions are,
`2Mg +SiO_(2) rarr 2MgO+Si,`
`" "2Mg+Si rarr Mg_(2)Si`
`Si+HCl rarr ` no reaction ,
`" "MgO+2HCl rarr MgCl_(2)+H_(2)O`
`Mg_(2)Si+4HCl rarr 2 MgCl_(2)+SiH_(4),`
`" " Mg_+2HCl rarr MgCl_(2)+H_(2)`
(Atomic wt. : Si = 28, Mg = 24)

Answer

9.8 gm