color(white)(mll)"Si"color(white)(ll) +color(white)(ll) "H"_2 color(white)(l)→color(white)(l) ("Si, H")mllSill+llH2l→l(Si, H)
"45.8 mg"color(white)(m) xcolor(white)(l) "mg"color(white)(mm) "50.7 mg"45.8 mgmxlmgmm50.7 mg
"Mass of H" = xcolor(white)(l) "mg" = "mass of (Si, H) – mass of Si"Mass of H=xlmg=mass of (Si, H) – mass of Si
"= 50.7 mg – 45.8 mg = 4.9 mg"= 50.7 mg – 45.8 mg = 4.9 mg
Our job is to calculate the ratio of the moles of each element.
"Moles of Si " = 45.8color(red)(cancel(color(black)("mg Si"))) × "1 mmol Si"/(28.08 color(red)(cancel(color(black)("mg Si")))) = "1.631 mmol Si"
"Moles of H" = 4.9 color(red)(cancel(color(black)("mg H"))) × "1 mmol H"/(1.008 color(red)(cancel(color(black)("mg H")))) = "4.86 mmol H"
To get the molar ratio, we divide each number of moles by the smallest number
("1.631").
From here on, I like to summarize the calculations in a table.
"Element"color(white)(X) "Mass/mg"color(white)(X) "mmol"color(white)(Xll) "Ratio"color(white)(mll)"Integers"
stackrel(—————————————————-——)(color(white)(m)"Si" color(white)(XXXm)45.8 color(white)(Xmm)"1.631"
color(white)(Xm)1color(white)(Xmmmm)1
color(white)(m)"H" color(white)(XXXXll)4.9 color(white)(mmm)"4.86" color(white)(Xmll)2.98 color(white)(XXXl)3
The empirical formula is "SiH"_3.
