Question #ded6c

Find the percentage mass of each element of salt, sodium chloride (NaCl)

Sodium = 23.0 grams ( to three significant digits)
Chlorine= 35.5 grams ( to three significant digits.)

The molar mass of Sodium Chloride is
`23.0 + 35.5 = 58.5` grams

The mass percent of sodium is

`23.0/58.5 = 39.3`%

`39.3% xx 47 .0 g = 18.5 g`

The mass percent of Chlorine is

`35.5/58.5 = 60.7`%

`60.7% xx 47.0g = 28.5 g`

Here's another way to do the calculation.

Start with the balanced equation:

`M_text(r): color(white)(ll)22.99color(white)(m)70.91color(white)(mll)58.44`
`color(white)(mmm)"2Na" + color(white)(l)"Cl"_2 → "2NaCl"`

Calculate the mass of `"Na"`

`"Moles of NaCl" = 47.0 color(red)(cancel(color(black)("g NaCl"))) × "1 mol NaCl"/(58.44 color(red)(cancel(color(black)("g NaCl")))) = "0.8042 mol NaCl"`

`"Moles of Na" = 0.8042 color(red)(cancel(color(black)("mol NaCl"))) × "2 mol Na"/(2 color(red)(cancel(color(black)("mol NaCl")))) = "0.8042 mol Na"`

`"Mass of Na" = 0.8042 color(red)(cancel(color(black)("mol Na"))) × "22.99 g Na"/(1 color(red)(cancel(color(black)("mol Na")))) = "18.5 g Na"`

Calculate the mass of `"Cl"_2`

`"Moles of Cl"_2 = 0.8042 color(red)(cancel(color(black)("mol NaCl"))) × "1 mol Cl"_2/(2 color(red)(cancel(color(black)("mol NaCl")))) = "0.4021 mol Na"`

`"Mass of Cl"_2 = 0.4021 color(red)(cancel(color(black)("mol Cl"_2))) × "70.91 g Cl"_2/(1 color(red)(cancel(color(black)("mol Cl"_2)))) = "28.5 g Na"`