what is the mass of a 257 mL sample of ethanol (ethyl alcohol) at 20 centigrade ? The density of ethanol at 20centigrade is 0.789 g|mL .

They tell you the density at the temperature in question.

Mass is density times volume. Have you learned that yet?

To find the mass of the ethanol sample, you can use the formula:

Mass = Volume x Density

Given that the volume of the ethanol sample is 257 mL and the density of ethanol at 20 degrees Celsius is 0.789 g/mL, you can plug these values into the formula:

Mass = 257 mL x 0.789 g/mL

Now, multiply the values:

Mass = 202.633 g

Therefore, the mass of the 257 mL sample of ethanol at 20 degrees Celsius is approximately 202.633 grams.