Question

List the % by mass for each element: First, add the total mass of 4 atoms of hydrogen, plus 2 atoms of carbon, plus 2 atoms of oxygen. Total mass = ___________________. To obtain percent by mass, divide the mass of each element by the mass of the total: H= _____% C= _____% O= _____%

Answer 1

Answer: H % by mass = 6.73%, C % by mass = 39.99%, O % by mass = 53.28%

Step-by-step explanation:

H atomic mass = 1.01 g/mol

C atomic mass = 12.01 g/mol

O atomic mass = 16.00 g/mol

To find the total mass, we multiply the number of atoms of an element by the element's atomic mass, then add those all together.

Total mass = 4(1.01 g) + 2(12.01 g) + 2(16.00 g)
= 60.06 g

% by mass:

H = 4(1.01 g)
= 4.04g
4.04g/60.06g = 0.0673 x 100%
H = 6.73% by mass

C = 2(12.01 g)
= 24.02g
24.02g/60.06g = 0.3999 x 100%
C = 39.99% by mass

O = 2(16.00 g)
= 32.00g
32.00g/60.06g = 0.5328 x 100%
O = 53.28% by mass

After finding each % by mass, I like to check my work by adding all the %s together to make sure they add up to 100.

6.73 + 39.99 + 53.28 = 100

I hope this helps! :)