125. how many molecules of ethanol (c₂h₅oh; the alcohol in alcoholic beverages) are present in 145 ml of…

Explanation:

Step1: Calculate the mass of ethanol

We know density $\rho=\frac{m}{V}$. Rearranging for mass $m = \rho V$. Given $\rho = 0.789\ g/cm^{3}$ and $V=145\ mL = 145\ cm^{3}$. So $m=0.789\ g/cm^{3}\times145\ cm^{3}=114.405\ g$.

Step2: Calculate the molar mass of ethanol

The molar - mass of $C_2H_5OH$: $M=(2\times12.01 + 6\times1.01+16.00)\ g/mol=(24.02 + 6.06 + 16.00)\ g/mol = 46.08\ g/mol$.

Step3: Calculate the number of moles of ethanol

The number of moles $n=\frac{m}{M}$. Substituting $m = 114.405\ g$ and $M = 46.08\ g/mol$, we get $n=\frac{114.405\ g}{46.08\ g/mol}=2.4827\ mol$.

Step4: Calculate the number of molecules of ethanol

Using Avogadro's number $N_A = 6.022\times10^{23}\ molecules/mol$, the number of molecules $N=n\times N_A$. So $N = 2.4827\ mol\times6.022\times10^{23}\ molecules/mol=1.4951\times10^{24}$ molecules.

Answer:

$1.4951\times 10^{24}$ molecules