Question

what is the percent composition by mass for each element in lactose c₁₂h₂₂o₁₁?

% c
% h
% o

Explanation:

Step1: Calculate percent composition of C

$$\%\text{C}=\frac{144.12}{342.34}\times100\%$$
$$\%\text{C}\approx42.10\%$$

Step2: Calculate percent composition of H

$$\%\text{H}=\frac{22.22}{342.34}\times100\%$$
$$\%\text{H}\approx6.49\%$$

Step3: Calculate percent composition of O

$$\%\text{O}=\frac{176.00}{342.34}\times100\%$$
$$\%\text{O}\approx51.41\%$$

Answer:

$\%$C: $42.10\%$; $\%$H: $6.49\%$; $\%$O: $51.41\%$