Question

What amount (moles) is represented by each of these samples?

$$\begin{gathered} \mathit{a}\mathbf{.}\mathbf{20}\mathbf{.}\mathbf{0}\mathit{m}\mathit{g}\mathit{c}\mathit{a}\mathit{f}\mathit{f}\mathit{e}\mathit{i}\mathit{n}\mathit{e}\mathbf{,}{\mathit{C}}_{\mathbf{8}}{\mathit{H}}_{\mathbf{10}}{\mathit{N}}_{\mathbf{4}}{\mathit{O}}_{\mathbf{2}} \\ \mathit{b}\mathbf{.}\mathbf{2}\mathbf{.}\mathbf{72}\mathbf{\times }{\mathbf{10}}^{\mathbf{21}}\mathit{m}\mathit{o}\mathit{l}\mathit{e}\mathit{c}\mathit{u}\mathit{l}\mathit{e}\mathit{s}\mathit{o}\mathit{f}\mathit{e}\mathit{t}\mathit{h}\mathit{a}\mathit{n}\mathit{o}\mathit{l}\mathbf{,}{\mathit{C}}_{\mathbf{2}}{\mathit{H}}_{\mathbf{5}}\mathit{O}\mathit{H} \\ \mathit{c}\mathbf{.}\mathbf{1}\mathbf{.}\mathbf{50}\mathit{g}\mathit{o}\mathit{f}\mathit{d}\mathit{r}\mathit{y}\mathit{i}\mathit{c}\mathit{e}\mathbf{,}\mathit{C}{\mathit{O}}_{\mathbf{2}} \end{gathered}$$

Short answer

The amounts of moles are:

a. 1.02 x 10^-4moles

b.4.51 x 10^-3

c. 0.034 moles

Step-by-step solution

Definition of mole

A mole is theamount of substance that contains many elementary entitiesof atoms in 0.012 kilogram of carbon 12.

a.20.0mgcaffeine,C8H10N4O2

The mass of caffeine:

$$\begin{gathered} =\frac{{\displaystyle 20.0\times {10}^{-3}g}}{194.2g/mol} \\ =1.02\times {10}^{-4}moles \end{gathered}$$

Step 3: b.2.72×1021moleculesofethanol,C2H5OH

The molecules of ethanol:

$$\begin{gathered} =\frac{2.72\times {10}^{21}}{6.022\times {10}^{23}} \\ =4.51\times {10}^{-3} \end{gathered}$$

Step 4: c.1.50gofdryice,CO2

The moles of carbon dioxide:

$$\begin{gathered} =\frac{1.50g}{44.01g/mol} \\ =0.034moles \end{gathered}$$