Question

1. (without a graphic organizer!) what is the percent by mass of oxygen in the compound $\ce{beco_{3}}$?

Explanation:

Step1: Calculate molar mass of $\text{BeCO}_3$

First, find atomic masses: $\text{Be}=9.01\ \text{g/mol}$, $\text{C}=12.01\ \text{g/mol}$, $\text{O}=16.00\ \text{g/mol}$.

$$\begin{align*} M(\text{BeCO}_3)&=9.01 + 12.01 + 3\times16.00\\ &=9.01 + 12.01 + 48.00\\ &=69.02\ \text{g/mol} \end{align*}$$

Step2: Find total mass of oxygen

$$ m(\text{O})=3\times16.00=48.00\ \text{g/mol} $$

Step3: Compute mass percent of oxygen

Use formula: $\text{Mass Percent}=\frac{\text{Total Mass of Element}}{\text{Molar Mass of Compound}}\times100\%$

$$ \text{Mass Percent of O}=\frac{48.00}{69.02}\times100\%\approx69.5\% $$

Answer:

Approximately 69.5%