Question

What is the percent by mass of sodium in Na2SO4

Answer 1

The answer is: the percent by mass of sodium is 32.4%.

The percent by mass is calculated by atomic mass of element multiply by number of that element in molecule divided by molecular mass of molecule.

Ar(Na) = 23; the relative atomic mass of sodium atom.

Mr(Na₂SO₄) = 2 · Ar(Na) + Ar(S) + 4 · Ar(O).

Mr(Na₂SO₄) = 2 · 23 + 32 + 4 · 16.

M(Na₂SO₄) = 142; relative moecular mass of sodium sulfate.

ω(Na)= 2 · Ar(Na) ÷ Mr(Na₂SO₄) · 100%.

ω(Na) = (2 · 23 ÷ 142) · 100%.

ω(Na) = 32.4 %.

Answer 2

The gram formula mass of Na2SO4 is 23*2+32+16*4=142. And the mass for sodium is 23*2=46. So the percent by mass is 46/142*100%=32.4%.