In this question, we need to find the number of moles of an Ethanol sample, based on the density and volume of the sample.
We have 175 mL of ethanol
0.789 of density
The conversion of cm3 to mL is 1 = 1
Which means that the density value is 0.789 g/mL
Since we have 175 mL, we can multiply the value of mass by the value of volume:
0.789 grams = 1 mL
x grams = 175 mL
x = 175 * 0.789
x = 138.075
Now we have the mass of ethanol, to find the number of moles we will use the molar mass, 46.07 g/mol
46.07 grams = 1 mol
138.075 grams = x moles
46.07x = 138.075
x = 138.075/46.07
x = 3 moles of ethanol
There are 3 moles of ethanol in 175 mL