Q. 7.95 - An Introduction to General, Organic, and Biological Chemistry

Question

How many moles are in $25.0$ g of each of the following compounds? ($7.3$)

a. ${\mathrm{CO}}_2$

b. ${\mathrm{Al}}_2{\mathrm{O}}_3$

c. ${\mathrm{MgCl}}_2$

Step-by-Step Solution

Answer

(a) The no. of moles of ${\mathrm{CO}}_2$in $25.0$ g are $0.568$ mole

(b) The no. of moles of ${\mathrm{Al}}_2{\mathrm{O}}_3$ in $25.0$ g are $0.245$ mole

(c) The no. of moles of ${\mathrm{MgCl}}_2$ in $25.0$ g are $0.263$ mole

Part (a) Step 1: Given information

We need to find no. of moles in given compound i.e. ${\mathrm{CO}}_2$ 

Part (a) Step 2: Explanation

We know that

Molar mass of ${\mathrm{CO}}_2$ is $44 \mathrm{g}/\mathrm{mole}$

And molar mass is equal to a mole

Therefore,

$$\begin{gathered} 44 \mathrm{g}=1 \mathrm{mole} \\ 25.0 \mathrm{g}=\frac{1 \mathrm{mol}}{44 \cancel{\mathrm{g}}}\times 25.0 \cancel{\mathrm{g}}=0.568 \mathrm{mole} \end{gathered}$$

Part (b) Step 1: Given information

We need to find no. of moles in given compound i.e. ${\mathrm{Al}}_2{\mathrm{O}}_3$

Part (b) Step 2: Explanation

We know that

Molar mass of ${\mathrm{Al}}_2{\mathrm{O}}_3$ is $102 \mathrm{g}/\mathrm{mole}$

And molar mass is equal to a mole 

Therefore,

$$\begin{gathered} 102 \mathrm{g}=1 \mathrm{mole} \\ 25.0 \mathrm{g}=\frac{1 \mathrm{mole}}{102 \cancel{\mathrm{g}}}\times 25.0 \cancel{\mathrm{g}}=0.245 \mathrm{mole} \end{gathered}$$

Part (c) Step 1: Given information

We need to find no. of moles in given compound i.e. ${\mathrm{MgCl}}_2$

Part (c) Step 2: Explanation

We know that

Molar mass of ${\mathrm{MgCl}}_2$ is $95.3 \mathrm{g}/\mathrm{mole}$

And molar mass is equal to a mole

Therefore,

$$\begin{gathered} 95.3 \mathrm{g}=1 \mathrm{mole} \\ 25.0 \mathrm{g}=\frac{1 \mathrm{mole}}{95.3 \cancel{\mathrm{g}}}\times 25 \cancel{\mathrm{g}}=0.263 \mathrm{mole} \end{gathered}$$