Question

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1. sodium sulfate is used in the manufacture of detergents. calculate the percent by mass of oxygen in sodium sulfate. round your answer to two decimal places. (0.5 points) *

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1. which does not describe a mole? (0.5 points) *

○ a unit used to count particles directly
○ avogadros number of molecules of a compound
○ the number of atoms in exactly 12 g of pure c-12
○ the si unit for the amount of a substance

Explanation:

Question 1

Step1: Determine the formula of sodium sulfate

Sodium sulfate has the formula $\ce{Na_{2}SO_{4}}$.

Step2: Calculate the molar mass of $\ce{Na_{2}SO_{4}}$

The molar mass of $\ce{Na}$ is approximately $22.99\ \text{g/mol}$, $\ce{S}$ is $32.07\ \text{g/mol}$, and $\ce{O}$ is $16.00\ \text{g/mol}$.
For $\ce{Na_{2}SO_{4}}$, the molar mass $M$ is:
\[

$$\begin{align*} M&=(2\times22.99)+32.07+(4\times16.00)\\ & = 45.98+32.07 + 64.00\\ &=142.05\ \text{g/mol} \end{align*}$$

\]

Step3: Calculate the total mass of oxygen in $\ce{Na_{2}SO_{4}}$

There are 4 oxygen atoms, so the mass of oxygen $m_{\ce{O}}$ is $4\times16.00 = 64.00\ \text{g/mol}$.

Step4: Calculate the percent by mass of oxygen

The percent by mass of an element in a compound is given by the formula:
\[
\text{Percent by mass}=\frac{\text{Mass of element in compound}}{\text{Molar mass of compound}}\times100\%
\]
Substituting the values:
\[
\text{Percent by mass of O}=\frac{64.00}{142.05}\times100\%\approx45.05\%
\]

• A mole is the SI unit for the amount of a substance (correct description).
• One mole of a compound contains Avogadro's number of molecules (correct description).
• One mole is defined as the number of atoms in exactly 12 g of pure C - 12 (correct description).
• A mole is not a unit used to count particles directly. We use moles to relate the number of particles (through Avogadro's number) to mass or volume, but we don't count particles directly with moles.

Answer:

$45.05\%$

Question 2