A laboratory group measures an excess of an unknown liquid. They add this to an

Question

A laboratory group measures an excess of an unknown liquid. They add this to an empty flask for which they calculate the volume. They heat the sample in a water bath until all liquid has been vaporized for several minutes. the sample is cooled and measured. Use their laboratory data (listed below) to answer the following questions: Calculate the mol of gas in the flask using the ideal gas law: Calculate the molar mass of the unknown: If a student added more than 4 mL of volatile liquid, would it affect the laboratory today? How? What if less liquid was added?

Explanation / Answer

a)

volume of flask = 275.6 mL = 0.2756 L

pressure = 0.914 atm

temperature = 84.1 + 273.15 = 357.25 K

P V = n R T

0.914 x 0.2756 = n x 0.0821 x 357.25

n = 8.588 x 10^-3

moles of gas in the flask = 8.588 x 10^-3

b)

mass of volatile liquid = 149.25 - 145.81 = 3.44 g

moles = mass / molar mass

8.588 x 10^-3 = 3.44 / molar mass

molar mass of unknown = 400.6 g/mol

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